Regenerate api_surface.json after merging develop

develop gained iterator+sentinel support for accept()/parse()/sax_parse()/
from_cbor()/from_msgpack()/from_ubjson()/from_bjdata()/from_bson() (#5205)
since this branch was created, which check_api_docs.yml's drift check caught
immediately: GitHub's pull_request trigger checks out the PR-vs-base merge
commit, not the PR branch in isolation, so CI was comparing the committed
api_surface.json (generated before that upstream change existed) against a
fresh extraction of a json.hpp that already had it.

This superseded an earlier, incorrect diagnosis of the same symptom (a
JSON_HAS_RANGES cross-environment pin) -- that fix remains in place since it's
still a real, independent determinism improvement for three other
JSON_HAS_RANGES-gated locations in type_traits.hpp, but it wasn't the actual
cause of this particular mismatch: these new overloads turned out to be
unconditional (SFINAE-gated via can_compare_ne, not preprocessor-gated), so
no environment-detection difference was involved here at all.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/workflows/check_api_docs.yml

@@ -0,0 +1,81 @@
+name: "Check API documentation"
+
+on:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  check_api_docs:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@bf7454d06d71f1098171f2acdf0cd4708d7b5920 # v2.20.0
+        with:
+          egress-policy: audit
+
+      - name: Checkout pull request
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+
+      - name: Install clang
+        # Used only as a subprocess for `clang++ -E -v` system-include-path discovery in
+        # extract_api.py; it does not need to version-match the pinned libclang pip wheel
+        # below, which does the actual AST parsing. Do not "fix" this to be version-matched.
+        run: sudo apt-get update && sudo apt-get install -y clang
+
+      - name: Install Python dependencies
+        run: pip install -r tools/api_checker/requirements.txt
+
+      - name: Extract API and regenerate the committed surface file
+        run: |
+          python3 tools/api_checker/extract_api.py \
+            --header include/nlohmann/json.hpp \
+            --include include \
+            --output /tmp/api_snapshot.json \
+            --surface-output tools/api_checker/api_surface.json
+
+      - name: "Check API documentation (Phase 1: advisory)"
+        # Surfaces missing/broken @sa links without failing the job while the backlog from the
+        # initial AST-based rollout is burned down. See tools/api_checker/POLICY.md and the PR
+        # that introduced this workflow for the two-phase rollout plan.
+        continue-on-error: true
+        run: |
+          python3 tools/api_checker/check_docs.py \
+            --snapshot /tmp/api_snapshot.json
+
+      - name: Check macro documentation (advisory only)
+        # Cross-checks docs/mkdocs/docs/api/macros/ pages against #define sites. Only checks the
+        # documented-macro-still-exists direction; never blocks CI. See POLICY.md.
+        run: python3 tools/api_checker/check_macros.py
+
+      - name: Check for uncommitted API surface changes
+        id: diff
+        run: |
+          mkdir -p ${{ github.workspace }}/patch
+          git diff --patch --no-color -- tools/api_checker/api_surface.json > ${{ github.workspace }}/patch/api_surface.patch
+          if [ -s ${{ github.workspace }}/patch/api_surface.patch ]; then
+            echo "tools/api_checker/api_surface.json is out of date. Diff:"
+            cat ${{ github.workspace }}/patch/api_surface.patch
+            echo "has_diff=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "has_diff=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      # Uploaded so contributors can fix their PR with `git apply api_surface.patch`
+      # instead of installing libclang locally.
+      - name: Upload patch
+        if: steps.diff.outputs.has_diff == 'true'
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: api-surface-patch
+          path: patch/api_surface.patch
+
+      - name: Fail if API surface file is not up to date
+        # Unlike the doc-backlog check above, this is purely mechanical regeneration with no
+        # backlog to phase in -- blocking from the start, matching check_amalgamation.yml's
+        # precedent. Contributors who add/remove/rename public API must regenerate and commit
+        # tools/api_checker/api_surface.json as part of their PR.
+        if: steps.diff.outputs.has_diff == 'true'
+        run: exit 1

.gitignore

@@ -3,6 +3,7 @@
 *.gcno
 *.gcda
 .DS_Store
+__pycache__/
 
 /.idea
 /cmake-build-*
@@ -43,5 +44,9 @@ venv
 
 nlohmann_json.spdx
 
+# api_checker: ephemeral, location/doc-status-sensitive working file (not the committed
+# release-tracking artifact -- see tools/api_checker/api_surface.json for that)
+/tools/api_checker/api_snapshot.json
+
 # Bazel-related
 MODULE.bazel.lock

README.md

@@ -106,7 +106,7 @@ Thanks everyone!
 
 :books: If you want to **learn more** about how to use the library, check out the rest of the [**README**](#examples), have a look at [**code examples**](https://github.com/nlohmann/json/tree/develop/docs/mkdocs/docs/examples), or browse through the [**help pages**](https://json.nlohmann.me).
 
-:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/) or have a look at the [quick reference](#quick-reference) below.
+:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/) or have a look at the [quick reference](#quick-reference) below. The public API surface is derived mechanically and checked for documentation coverage by the tooling in [`tools/api_checker/`](tools/api_checker/), whose [POLICY.md](tools/api_checker/POLICY.md) defines what counts as public API and what stability is guaranteed.
 
 :bug: If you found a **bug**, please check the [**FAQ**](https://json.nlohmann.me/home/faq/) if it is a known issue or the result of a design decision. Please also have a look at the [**issue list**](https://github.com/nlohmann/json/issues) before you [**create a new issue**](https://github.com/nlohmann/json/issues/new/choose). Please provide as much information as possible to help us understand and reproduce your issue.
 

docs/mkdocs/docs/api/basic_json/basic_json.md

@@ -420,7 +420,9 @@ basic_json(basic_json&& other) noexcept;
 1. Since version 1.0.0.
 2. Since version 1.0.0.
 3. Since version 2.1.0.
-4. Since version 3.2.0.
+4. Since version 3.2.0. Also initializes the position reported by
+   [`start_pos()`](start_pos.md)/[`end_pos()`](end_pos.md) from `val` when
+   [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) is enabled, since version 3.12.0.
 5. Since version 1.0.0.
 6. Since version 1.0.0.
 7. Since version 1.0.0.

docs/mkdocs/docs/api/basic_json/bjdata_version_t.md

@@ -0,0 +1,38 @@
+# <small>nlohmann::basic_json::</small>bjdata_version_t
+
+```cpp
+enum class bjdata_version_t
+{
+    draft2,
+    draft3,
+};
+```
+
+This enumeration is used in the [`to_bjdata`](to_bjdata.md) function to choose which draft version of
+the BJData specification to encode ND-array extensions for:
+
+draft2
+:   encode using the BJData Draft 2 ND-array format
+
+draft3
+:   encode using the BJData Draft 3 ND-array format
+
+## Examples
+
+??? example
+
+    The example shows how `bjdata_version_t` selects the BJData draft used by `to_bjdata`.
+
+    ```cpp
+    --8<-- "examples/bjdata_version_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/bjdata_version_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.12.0.

docs/mkdocs/docs/api/basic_json/initializer_list_t.md

@@ -0,0 +1,32 @@
+# <small>nlohmann::basic_json::</small>initializer_list_t
+
+```cpp
+using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
+```
+
+The type used for the initializer-list [constructor](basic_json.md) (overload 5) and for functions
+such as [`operator=`](operator=.md) that accept a braced-init-list of JSON values. Each element wraps a
+`basic_json` value or something convertible to one, deferring the decision of whether the list should be
+parsed as a JSON array or a JSON object to the constructor itself.
+
+See the [constructor](basic_json.md) documentation for how `initializer_list_t` values are interpreted.
+
+## Examples
+
+??? example
+
+    The example shows how an `initializer_list_t` is used to construct a JSON value.
+
+    ```cpp
+    --8<-- "examples/initializer_list_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/initializer_list_t.output"
+    ```
+
+## Version history
+
+- Since version 1.0.0.

docs/mkdocs/docs/api/basic_json/json_sax_t.md

@@ -0,0 +1,31 @@
+# <small>nlohmann::basic_json::</small>json_sax_t
+
+```cpp
+using json_sax_t = json_sax<basic_json>;
+```
+
+The [`json_sax`](../json_sax/index.md) interface bound to this `basic_json` specialization, i.e. with
+`BasicJsonType` fixed to `basic_json`. Used as the SAX interface type by [`sax_parse`](sax_parse.md) and
+other SAX-based parsing functions.
+
+See [`nlohmann::json_sax`](../json_sax/index.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `json_sax_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/basic_json/operator=.md

@@ -51,3 +51,5 @@ Linear.
 ## Version history
 
 - Added in version 1.0.0.
+- The `noexcept` specification was extended to also depend on
+  [`json_base_class_t`](json_base_class_t.md)'s move-assignment in version 3.11.3.

docs/mkdocs/docs/api/basic_json/operator_ValueType.md

@@ -85,3 +85,8 @@ Linear in the size of the JSON value.
 - Since version 1.0.0.
 - Macros `JSON_EXPLICIT`/[`JSON_USE_IMPLICIT_CONVERSIONS`](../macros/json_use_implicit_conversions.md) added
   in version 3.9.0.
+- The exclusion of `std::any` from this conversion became conditional on
+  [`JSON_HAS_STATIC_RTTI`](../macros/json_has_static_rtti.md) in version 3.11.3.
+- `std::optional<T>` excluded from this conversion in version 3.13.0; use
+  [`get<std::optional<T>>()`](get.md)/[`get_to()`](get_to.md) instead (see
+  [Converting values](../../features/conversions.md)).

docs/mkdocs/docs/api/byte_container_with_subtype/container_type.md

@@ -0,0 +1,32 @@
+# <small>nlohmann::byte_container_with_subtype::</small>container_type
+
+```cpp
+using container_type = BinaryType;
+```
+
+The type of the underlying binary container, forwarded from the `BinaryType` template parameter that
+`byte_container_with_subtype` is instantiated with. `byte_container_with_subtype` publicly inherits from
+`container_type`.
+
+See [`basic_json::binary_t`](../basic_json/binary_t.md) for the type typically used to instantiate
+`BinaryType`.
+
+## Examples
+
+??? example
+
+    The example shows the type `container_type`.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__container_type.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__container_type.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.

docs/mkdocs/docs/api/byte_container_with_subtype/operator_eq.md

@@ -0,0 +1,45 @@
+# <small>nlohmann::byte_container_with_subtype::</small>operator==
+
+```cpp
+bool operator==(const byte_container_with_subtype& rhs) const;
+```
+
+Compares two `byte_container_with_subtype` values for equality by comparing the underlying binary
+container, the subtype, and whether a subtype is set.
+
+## Parameters
+
+`rhs` (in)
+:   value to compare `*this` against
+
+## Return value
+
+whether `*this` and `rhs` are equal
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear in the size of the underlying binary container.
+
+## Examples
+
+??? example
+
+    The example demonstrates comparing `byte_container_with_subtype` values.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__operator_eq.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__operator_eq.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.

docs/mkdocs/docs/api/byte_container_with_subtype/operator_ne.md

@@ -0,0 +1,45 @@
+# <small>nlohmann::byte_container_with_subtype::</small>operator!=
+
+```cpp
+bool operator!=(const byte_container_with_subtype& rhs) const;
+```
+
+Compares two `byte_container_with_subtype` values for inequality. Implemented as the negation of
+[`operator==`](operator_eq.md).
+
+## Parameters
+
+`rhs` (in)
+:   value to compare `*this` against
+
+## Return value
+
+whether `*this` and `rhs` are not equal
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear in the size of the underlying binary container.
+
+## Examples
+
+??? example
+
+    The example demonstrates comparing `byte_container_with_subtype` values.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__operator_ne.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__operator_ne.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.

docs/mkdocs/docs/api/byte_container_with_subtype/subtype_type.md

@@ -0,0 +1,28 @@
+# <small>nlohmann::byte_container_with_subtype::</small>subtype_type
+
+```cpp
+using subtype_type = std::uint64_t;
+```
+
+The type used to store the optional binary subtype tag. See [`subtype`](subtype.md) and
+[`set_subtype`](set_subtype.md).
+
+## Examples
+
+??? example
+
+    The example shows the type `subtype_type`.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__subtype_type.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__subtype_type.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.

docs/mkdocs/docs/api/json_sax/binary_t.md

@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>binary_t
+
+```cpp
+using binary_t = typename BasicJsonType::binary_t;
+```
+
+The type used by the [`binary`](binary.md) callback for JSON binary values, forwarded from the
+`BasicJsonType` template parameter.
+
+See [`basic_json::binary_t`](../basic_json/binary_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `binary_t` and its relation to `basic_json::binary_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__binary_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__binary_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.8.0.

docs/mkdocs/docs/api/json_sax/json_sax.md

@@ -0,0 +1,33 @@
+# <small>nlohmann::json_sax::</small>json_sax
+
+```cpp
+// (1)
+json_sax() = default;
+
+// (2)
+json_sax(const json_sax&) = default;
+
+// (3)
+json_sax(json_sax&&) noexcept = default;
+```
+
+1. Default constructor.
+2. Copy constructor.
+3. Move constructor.
+
+`json_sax` is a pure abstract base class with no data members of its own, so all three constructors are
+defaulted and only exist to make derived SAX consumers explicitly copyable/movable.
+
+## Exception safety
+
+No-throw guarantee: none of these constructors throw exceptions.
+
+## Complexity
+
+Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/json_sax/number_float_t.md

@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>number_float_t
+
+```cpp
+using number_float_t = typename BasicJsonType::number_float_t;
+```
+
+The type used by the [`number_float`](number_float.md) callback for JSON floating-point numbers,
+forwarded from the `BasicJsonType` template parameter.
+
+See [`basic_json::number_float_t`](../basic_json/number_float_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `number_float_t` and its relation to `basic_json::number_float_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__number_float_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__number_float_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/json_sax/number_integer_t.md

@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>number_integer_t
+
+```cpp
+using number_integer_t = typename BasicJsonType::number_integer_t;
+```
+
+The type used by the [`number_integer`](number_integer.md) callback for JSON integer numbers, forwarded
+from the `BasicJsonType` template parameter.
+
+See [`basic_json::number_integer_t`](../basic_json/number_integer_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `number_integer_t` and its relation to `basic_json::number_integer_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__number_integer_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__number_integer_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/json_sax/number_unsigned_t.md

@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>number_unsigned_t
+
+```cpp
+using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+```
+
+The type used by the [`number_unsigned`](number_unsigned.md) callback for JSON unsigned integer numbers,
+forwarded from the `BasicJsonType` template parameter.
+
+See [`basic_json::number_unsigned_t`](../basic_json/number_unsigned_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `number_unsigned_t` and its relation to `basic_json::number_unsigned_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__number_unsigned_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__number_unsigned_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/json_sax/operator=.md

@@ -0,0 +1,29 @@
+# <small>nlohmann::json_sax::</small>operator=
+
+```cpp
+// (1)
+json_sax& operator=(const json_sax&) = default;
+
+// (2)
+json_sax& operator=(json_sax&&) noexcept = default;
+```
+
+1. Copy assignment operator.
+2. Move assignment operator.
+
+`json_sax` is a pure abstract base class with no data members of its own, so both assignment operators
+are defaulted and only exist to make derived SAX consumers explicitly copy-/move-assignable.
+
+## Exception safety
+
+No-throw guarantee: neither operator throws exceptions.
+
+## Complexity
+
+Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/json_sax/string_t.md

@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>string_t
+
+```cpp
+using string_t = typename BasicJsonType::string_t;
+```
+
+The type used by the [`string`](string.md) and [`key`](key.md) callbacks for JSON strings and object
+keys, forwarded from the `BasicJsonType` template parameter.
+
+See [`basic_json::string_t`](../basic_json/string_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `string_t` and its relation to `basic_json::string_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__string_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__string_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/json_sax/~json_sax.md

@@ -0,0 +1,22 @@
+# <small>nlohmann::json_sax::</small>~json_sax
+
+```cpp
+virtual ~json_sax() = default;
+```
+
+Destructor. Virtual to allow proper destruction of derived SAX consumer classes through a
+pointer/reference to `json_sax`.
+
+## Exception safety
+
+No-throw guarantee: this destructor never throws exceptions.
+
+## Complexity
+
+Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.2.0.

docs/mkdocs/docs/api/macros/nlohmann_define_derived_type.md

@@ -57,8 +57,7 @@ Summary:
 :   name of the base type (class, struct) `type` is derived from
 
 `member` (in)
-:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated
-    list, which may also be empty
+:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
 
 ## Default definition
 
@@ -128,20 +127,6 @@ void to_json(BasicJsonType& j, const B& b) {
     - Macros 4, 5, and 6 have the same prerequisites of [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](nlohmann_define_type_non_intrusive.md).
     - Serialization/deserialization of base types must be defined.
 
-!!! info "Derived types without own members"
-
-    The member list may be empty. The macro then generates a `to_json`/`from_json` pair that only delegates to
-    the base type, so `type` serializes exactly like `base_type`:
-
-    ```cpp
-    struct derived : base
-    {
-        NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(derived, base)
-    };
-    ```
-
-    The `WITH_NAMES` variants do not support this.
-
 !!! warning "Implementation limits"
 
     See Implementation limits for [NLOHMANN_DEFINE_TYPE_INTRUSIVE](nlohmann_define_type_intrusive.md) and

docs/mkdocs/docs/api/macros/nlohmann_define_type_intrusive.md

@@ -33,8 +33,7 @@ Summary:
 :   name of the type (class, struct) to serialize/deserialize
 
 `member` (in)
-:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated
-    list, which may also be empty
+:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
 
 ## Default definition
 
@@ -59,20 +58,6 @@ See the examples below for the concrete generated code.
 
 [GetNonDefNonCopy]: ../../features/arbitrary_types.md#how-can-i-use-get-for-non-default-constructiblenon-copyable-types
 
-!!! info "Types without members"
-
-    The member list may be empty. The macro then generates a `to_json` that produces an empty JSON object
-    `#!json {}`, and a `from_json` that reads no members:
-
-    ```cpp
-    struct marker
-    {
-        NLOHMANN_DEFINE_TYPE_INTRUSIVE(marker)
-    };
-    ```
-
-    The `WITH_NAMES` variants do not support this.
-
 !!! warning "Implementation limits"
 
     - The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types

docs/mkdocs/docs/api/macros/nlohmann_define_type_non_intrusive.md

@@ -33,8 +33,7 @@ Summary:
 :   name of the type (class, struct) to serialize/deserialize
 
 `member` (in)
-:   name of the (public) member variable to serialize/deserialize; up to 63 members can be given as a
-    comma-separated list, which may also be empty
+:   name of the (public) member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
 
 ## Default definition
 
@@ -60,18 +59,6 @@ See the examples below for the concrete generated code.
 
 [GetNonDefNonCopy]: ../../features/arbitrary_types.md#how-can-i-use-get-for-non-default-constructiblenon-copyable-types
 
-!!! info "Types without members"
-
-    The member list may be empty. The macro then generates a `to_json` that produces an empty JSON object
-    `#!json {}`, and a `from_json` that reads no members:
-
-    ```cpp
-    struct marker {};
-    NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(marker)
-    ```
-
-    The `WITH_NAMES` variants do not support this.
-
 !!! warning "Implementation limits"
 
     - The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types

docs/mkdocs/docs/api/ordered_json.md

@@ -8,7 +8,7 @@ This type preserves the insertion order of object keys.
 
 ## Iterator invalidation
 
-The type is based on [`ordered_map`](ordered_map.md) which in turn uses a `std::vector` to store object elements.
+The type is based on [`ordered_map`](ordered_map/index.md) which in turn uses a `std::vector` to store object elements.
 Therefore, adding object elements can yield a reallocation in which case all iterators (including the
 [`end()`](basic_json/end.md) iterator) and all references to the elements are invalidated. Also, any iterator or
 reference after the insertion point will point to the same index, which is now a different value.
@@ -31,7 +31,7 @@ reference after the insertion point will point to the same index, which is now a
 
 ## See also
 
-- [ordered_map](ordered_map.md)
+- [ordered_map](ordered_map/index.md)
 - [Object Order](../features/object_order.md)
 
 ## Version history

docs/mkdocs/docs/api/ordered_map/Container.md

@@ -0,0 +1,28 @@
+# <small>nlohmann::ordered_map::</small>Container
+
+```cpp
+using Container = std::vector<std::pair<const Key, T>, Allocator>;
+```
+
+The base container type that `ordered_map` publicly inherits from. Elements are stored in insertion
+order as `#!cpp std::pair<const Key, T>` entries in a `std::vector`.
+
+## Examples
+
+??? example
+
+    The example shows the type `Container`.
+
+    ```cpp
+    --8<-- "examples/ordered_map__Container.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__Container.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).

docs/mkdocs/docs/api/ordered_map/at.md

@@ -0,0 +1,61 @@
+# <small>nlohmann::ordered_map::</small>at
+
+```cpp
+// (1)
+T& at(const key_type& key);
+const T& at(const key_type& key) const;
+
+// (2)
+template<class KeyType>
+T& at(KeyType&& key);
+template<class KeyType>
+const T& at(KeyType&& key) const;
+```
+
+1. Returns a reference to the value mapped to `key`.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup, e.g. looking up by a `#!cpp const char*` without constructing a temporary
+   `key_type`). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to find
+
+## Return value
+
+reference to the mapped value of the element with key equal to `key`
+
+## Exceptions
+
+Throws `std::out_of_range` if no element with key `key` exists.
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `at` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__at.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__at.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/count.md

@@ -0,0 +1,53 @@
+# <small>nlohmann::ordered_map::</small>count
+
+```cpp
+// (1)
+size_type count(const key_type& key) const;
+
+// (2)
+template<class KeyType>
+size_type count(KeyType&& key) const;
+```
+
+1. Returns the number of elements with key equal to `key` (0 or 1, since keys are unique).
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the elements to count
+
+## Return value
+
+number of elements with key equal to `key` (0 or 1)
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `count` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__count.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__count.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/emplace.md

@@ -0,0 +1,58 @@
+# <small>nlohmann::ordered_map::</small>emplace
+
+```cpp
+// (1)
+std::pair<iterator, bool> emplace(const key_type& key, T&& t);
+
+// (2)
+template<class KeyType>
+std::pair<iterator, bool> emplace(KeyType&& key, T&& t);
+```
+
+1. Inserts `#!cpp {key, t}` if no element with an equal key already exists (per [`key_compare`](key_compare.md)),
+   appending it at the end to preserve insertion order. If an equal key already exists, does nothing.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to insert
+
+`t` (in)
+:   value of the element to insert
+
+## Return value
+
+pair of an iterator to the (possibly newly inserted) element, and a `bool` that is `true` if insertion
+took place and `false` if an element with an equal key already existed
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `emplace` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__emplace.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__emplace.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/erase.md

@@ -0,0 +1,75 @@
+# <small>nlohmann::ordered_map::</small>erase
+
+```cpp
+// (1)
+size_type erase(const key_type& key);
+
+// (2)
+template<class KeyType>
+size_type erase(KeyType&& key);
+
+// (3)
+iterator erase(iterator pos);
+
+// (4)
+iterator erase(iterator first, iterator last);
+```
+
+1. Removes the element with key equal to `key`, if any, preserving the relative order of the remaining
+   elements.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+3. Removes the element at `pos`.
+4. Removes the elements in range `[first, last)`.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to remove
+
+`pos` (in)
+:   iterator to the element to remove
+
+`first` (in)
+:   iterator to the first element to remove
+
+`last` (in)
+:   iterator one past the last element to remove
+
+## Return value
+
+1. number of elements removed (0 or 1)
+2. number of elements removed (0 or 1)
+3. iterator following the removed element
+4. iterator following the last removed element
+
+## Complexity
+
+Linear in the number of elements (elements after the removed one(s) are shifted to keep storage
+contiguous).
+
+## Examples
+
+??? example
+
+    The example shows how `erase` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__erase.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__erase.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/find.md

@@ -0,0 +1,56 @@
+# <small>nlohmann::ordered_map::</small>find
+
+```cpp
+// (1)
+iterator find(const key_type& key);
+const_iterator find(const key_type& key) const;
+
+// (2)
+template<class KeyType>
+iterator find(KeyType&& key);
+template<class KeyType>
+const_iterator find(KeyType&& key) const;
+```
+
+1. Returns an iterator to the element with key equal to `key`, or `end()` if no such element exists.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to find
+
+## Return value
+
+iterator to the element with key equal to `key`, or `end()` if not found
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `find` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__find.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__find.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/index.md

@@ -6,7 +6,7 @@ template<class Key, class T, class IgnoredLess = std::less<Key>,
 struct ordered_map : std::vector<std::pair<const Key, T>, Allocator>;
 ```
 
-A minimal map-like container that preserves insertion order for use within [`nlohmann::ordered_json`](ordered_json.md)
+A minimal map-like container that preserves insertion order for use within [`nlohmann::ordered_json`](../ordered_json.md)
 (`nlohmann::basic_json<ordered_map>`).
 
 ## Template parameters
@@ -32,12 +32,12 @@ case all iterators (including the `end()` iterator) and all references to the el
 
 - **key_type** - key type (`Key`)
 - **mapped_type** - mapped type (`T`)
-- **Container** - base container type (`#!cpp std::vector<std::pair<const Key, T>, Allocator>`)
+- [**Container**](Container.md) - base container type (`#!cpp std::vector<std::pair<const Key, T>, Allocator>`)
 - **iterator**
 - **const_iterator**
 - **size_type**
 - **value_type**
-- **key_compare** - key comparison function
+- [**key_compare**](key_compare.md) - key comparison function
 ```cpp
 std::equal_to<Key>  // until C++14
 
@@ -46,15 +46,16 @@ std::equal_to<>     // since C++14
 
 ## Member functions
 
-- (constructor)
-- (destructor)
-- **emplace**
-- **operator\[\]**
-- **at**
-- **erase**
-- **count**
-- **find**
-- **insert**
+- [(constructor)](ordered_map.md)
+- [(destructor)](~ordered_map.md)
+- [**operator=**](operator=.md)
+- [**emplace**](emplace.md)
+- [**operator\[\]**](operator[].md)
+- [**at**](at.md)
+- [**erase**](erase.md)
+- [**count**](count.md)
+- [**find**](find.md)
+- [**insert**](insert.md)
 
 ## Examples
 
@@ -74,9 +75,9 @@ std::equal_to<>     // since C++14
 
 ## See also
 
-- [ordered_json](ordered_json.md)
+- [ordered_json](../ordered_json.md)
 
 ## Version history
 
-- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](ordered_json.md).
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
 - Added **key_compare** member in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/insert.md

@@ -0,0 +1,63 @@
+# <small>nlohmann::ordered_map::</small>insert
+
+```cpp
+// (1)
+std::pair<iterator, bool> insert(value_type&& value);
+std::pair<iterator, bool> insert(const value_type& value);
+
+// (2)
+template<typename InputIt>
+void insert(InputIt first, InputIt last);
+```
+
+1. Inserts `value` if no element with an equal key already exists (per [`key_compare`](key_compare.md)),
+   appending it at the end to preserve insertion order. If an equal key already exists, does nothing.
+2. Inserts the elements from range `[first, last)`, in iteration order, applying the same equal-key rule
+   as (1) to each element.
+
+## Template parameters
+
+`InputIt`
+:   an input iterator type
+
+## Parameters
+
+`value` (in)
+:   value to insert
+
+`first` (in)
+:   iterator to the first element to insert
+
+`last` (in)
+:   iterator one past the last element to insert
+
+## Return value
+
+1. pair of an iterator to the (possibly newly inserted) element, and a `bool` that is `true` if insertion
+   took place and `false` if an element with an equal key already existed
+2. (none)
+
+## Complexity
+
+1. Linear in the number of elements.
+2. Linear in the distance between `first` and `last`, times linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `insert` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__insert.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__insert.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).

docs/mkdocs/docs/api/ordered_map/key_compare.md

@@ -0,0 +1,34 @@
+# <small>nlohmann::ordered_map::</small>key_compare
+
+```cpp
+using key_compare = std::equal_to<Key>;  // until C++14
+
+using key_compare = std::equal_to<>;     // since C++14
+```
+
+The comparator used to determine key equality when looking up elements. Unlike `std::map`, `ordered_map`
+uses linear search with `key_compare` rather than an ordering relation, since element order reflects
+insertion order rather than key order.
+
+Since C++14, the transparent `#!cpp std::equal_to<>` is used, which enables heterogeneous lookup (e.g.
+looking up by a `#!cpp const char*` key without constructing a temporary `Key`).
+
+## Examples
+
+??? example
+
+    The example shows how `key_compare` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__key_compare.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__key_compare.output"
+    ```
+
+## Version history
+
+- Added in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/operator=.md

@@ -0,0 +1,32 @@
+# <small>nlohmann::ordered_map::</small>operator=
+
+```cpp
+// (1)
+ordered_map& operator=(const ordered_map& other);
+
+// (2)
+ordered_map& operator=(ordered_map&& other) noexcept(std::is_nothrow_move_assignable<Container>::value);
+```
+
+1. Copy assignment operator.
+2. Move assignment operator.
+
+## Parameters
+
+`other` (in)
+:   value to assign from
+
+## Return value
+
+`*this`
+
+## Complexity
+
+1. Linear in the size of `other`.
+2. Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).

docs/mkdocs/docs/api/ordered_map/operator[].md

@@ -0,0 +1,62 @@
+# <small>nlohmann::ordered_map::</small>operator[]
+
+```cpp
+// (1)
+T& operator[](const key_type& key);
+const T& operator[](const key_type& key) const;
+
+// (2)
+template<class KeyType>
+T& operator[](KeyType&& key);
+template<class KeyType>
+const T& operator[](KeyType&& key) const;
+```
+
+1. Returns a reference to the value mapped to `key`, inserting a default-constructed `T` (non-`const`
+   overload only) if no such element exists yet.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to find or insert
+
+## Return value
+
+reference to the mapped value of the element with key equal to `key`
+
+## Exceptions
+
+The `const` overloads throw `std::out_of_range` if no element with key `key` exists (they delegate to
+[`at`](at.md)).
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `operator[]` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__operator_idx.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__operator_idx.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.

docs/mkdocs/docs/api/ordered_map/ordered_map.md

@@ -0,0 +1,66 @@
+# <small>nlohmann::ordered_map::</small>ordered_map
+
+```cpp
+// (1)
+ordered_map() noexcept(noexcept(Container()));
+
+// (2)
+explicit ordered_map(const Allocator& alloc) noexcept(noexcept(Container(alloc)));
+
+// (3)
+template <class It>
+ordered_map(It first, It last, const Allocator& alloc = Allocator());
+
+// (4)
+ordered_map(std::initializer_list<value_type> init, const Allocator& alloc = Allocator());
+
+// (5)
+ordered_map(const ordered_map&) = default;
+
+// (6)
+ordered_map(ordered_map&&) noexcept(std::is_nothrow_move_constructible<Container>::value) = default;
+```
+
+1. Default constructor. Creates an empty `ordered_map`.
+2. Creates an empty `ordered_map` using the given allocator.
+3. Creates an `ordered_map` from the elements in range `[first, last)`, inserted in iteration order.
+4. Creates an `ordered_map` from an initializer list of key/value pairs, inserted in list order.
+5. Copy constructor.
+6. Move constructor.
+
+These constructors are declared explicitly (rather than inherited via `#!cpp using Container::Container`)
+because older compilers (GCC <= 5.5, Xcode <= 9.4) do not handle the inherited constructors correctly.
+
+## Template parameters
+
+`It`
+:   an input iterator type
+
+## Parameters
+
+`alloc` (in)
+:   allocator to use for the underlying container
+
+`first` (in)
+:   iterator to the first element to insert
+
+`last` (in)
+:   iterator one past the last element to insert
+
+`init` (in)
+:   initializer list of key/value pairs to insert
+
+## Complexity
+
+1. Constant.
+2. Constant.
+3. Linear in the distance between `first` and `last`.
+4. Linear in the size of `init`.
+5. Linear in the size of `other`.
+6. Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).

docs/mkdocs/docs/api/ordered_map/~ordered_map.md

@@ -0,0 +1,17 @@
+# <small>nlohmann::ordered_map::</small>~ordered_map
+
+```cpp
+~ordered_map() = default;
+```
+
+Destroys the `ordered_map` and frees all allocated memory.
+
+## Complexity
+
+Linear in the number of elements.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).

docs/mkdocs/docs/examples/bjdata_version_t.cpp

@@ -0,0 +1,21 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // an empty binary value is encoded differently by the two drafts:
+    // draft2 omits the optimized type marker for an empty byte array,
+    // while draft3 always writes it
+    json j = json::binary({});
+
+    // encode using BJData draft2 (the default)
+    auto v_draft2 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft2);
+
+    // encode using BJData draft3
+    auto v_draft3 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft3);
+
+    std::cout << "draft2 size: " << v_draft2.size() << '\n'
+              << "draft3 size: " << v_draft3.size() << std::endl;
+}

docs/mkdocs/docs/examples/bjdata_version_t.output

@@ -0,0 +1,2 @@
+draft2 size: 4
+draft3 size: 6

docs/mkdocs/docs/examples/byte_container_with_subtype__container_type.cpp

@@ -0,0 +1,11 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<byte_container_with_subtype::container_type, std::vector<std::uint8_t>>::value
+              << std::endl;
+}

docs/mkdocs/docs/examples/byte_container_with_subtype__container_type.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/byte_container_with_subtype__operator_eq.cpp

@@ -0,0 +1,15 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    byte_container_with_subtype c1({0xca, 0xfe});
+    byte_container_with_subtype c2({0xca, 0xfe});
+    byte_container_with_subtype c3({0xca, 0xfe}, 42);
+
+    std::cout << std::boolalpha
+              << "c1 == c2: " << (c1 == c2) << '\n'
+              << "c1 == c3: " << (c1 == c3) << std::endl;
+}

docs/mkdocs/docs/examples/byte_container_with_subtype__operator_eq.output

@@ -0,0 +1,2 @@
+c1 == c2: true
+c1 == c3: false

docs/mkdocs/docs/examples/byte_container_with_subtype__operator_ne.cpp

@@ -0,0 +1,15 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    byte_container_with_subtype c1({0xca, 0xfe});
+    byte_container_with_subtype c2({0xca, 0xfe});
+    byte_container_with_subtype c3({0xca, 0xfe}, 42);
+
+    std::cout << std::boolalpha
+              << "c1 != c2: " << (c1 != c2) << '\n'
+              << "c1 != c3: " << (c1 != c3) << std::endl;
+}

docs/mkdocs/docs/examples/byte_container_with_subtype__operator_ne.output

@@ -0,0 +1,2 @@
+c1 != c2: false
+c1 != c3: true

docs/mkdocs/docs/examples/byte_container_with_subtype__subtype_type.cpp

@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<byte_container_with_subtype::subtype_type, std::uint64_t>::value << std::endl;
+}

docs/mkdocs/docs/examples/byte_container_with_subtype__subtype_type.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/initializer_list_t.cpp

@@ -0,0 +1,13 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // an initializer_list_t is what a braced-init-list of JSON values is deduced as
+    json::initializer_list_t init = {"a", 1, 2.0, false};
+
+    json j(init);
+    std::cout << j.dump() << std::endl;
+}

docs/mkdocs/docs/examples/initializer_list_t.output

@@ -0,0 +1 @@
+["a",1,2.0,false]

docs/mkdocs/docs/examples/json_sax__binary_t.cpp

@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::binary_t, json::binary_t>::value << std::endl;
+}

docs/mkdocs/docs/examples/json_sax__binary_t.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/json_sax__number_float_t.cpp

@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::number_float_t, json::number_float_t>::value << std::endl;
+}

docs/mkdocs/docs/examples/json_sax__number_float_t.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/json_sax__number_integer_t.cpp

@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::number_integer_t, json::number_integer_t>::value << std::endl;
+}

docs/mkdocs/docs/examples/json_sax__number_integer_t.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/json_sax__number_unsigned_t.cpp

@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::number_unsigned_t, json::number_unsigned_t>::value << std::endl;
+}

docs/mkdocs/docs/examples/json_sax__number_unsigned_t.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/json_sax__string_t.cpp

@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::string_t, json::string_t>::value << std::endl;
+}

docs/mkdocs/docs/examples/json_sax__string_t.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/json_sax_t.cpp

@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t, nlohmann::json_sax<json>>::value << std::endl;
+}

docs/mkdocs/docs/examples/json_sax_t.output

@@ -0,0 +1 @@
+true

docs/mkdocs/docs/examples/ordered_map__Container.cpp

@@ -0,0 +1,12 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    using Map = nlohmann::ordered_map<std::string, int>;
+
+    std::cout << std::boolalpha
+              << "Container is std::vector<std::pair<const Key, T>>: "
+              << std::is_same<Map::Container, std::vector<std::pair<const std::string, int>>>::value
+              << std::endl;
+}

docs/mkdocs/docs/examples/ordered_map__Container.output

@@ -0,0 +1 @@
+Container is std::vector<std::pair<const Key, T>>: true

docs/mkdocs/docs/examples/ordered_map__at.cpp

@@ -0,0 +1,26 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+    m["two"] = 2;
+
+    // access an existing element
+    std::cout << "m.at(\"one\") = " << m.at("one") << std::endl;
+
+    // modify through the reference returned by at()
+    m.at("two") = 22;
+    std::cout << "m.at(\"two\") = " << m.at("two") << std::endl;
+
+    // accessing a missing key throws
+    try
+    {
+        m.at("three");
+    }
+    catch (const std::out_of_range& e)
+    {
+        std::cout << "exception: " << e.what() << std::endl;
+    }
+}

docs/mkdocs/docs/examples/ordered_map__at.output

@@ -0,0 +1,3 @@
+m.at("one") = 1
+m.at("two") = 22
+exception: key not found

docs/mkdocs/docs/examples/ordered_map__count.cpp

@@ -0,0 +1,12 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+
+    std::cout << std::boolalpha
+              << "m.count(\"one\") = " << m.count("one") << '\n'
+              << "m.count(\"two\") = " << m.count("two") << std::endl;
+}

docs/mkdocs/docs/examples/ordered_map__count.output

@@ -0,0 +1,2 @@
+m.count("one") = 1
+m.count("two") = 0

docs/mkdocs/docs/examples/ordered_map__emplace.cpp

@@ -0,0 +1,15 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, std::string> m;
+
+    // emplace a new element
+    auto res1 = m.emplace("one", "eins");
+    std::cout << std::boolalpha << "inserted: " << res1.second << ", value: " << res1.first->second << std::endl;
+
+    // emplace with an already-existing key: no-op, returns the existing element
+    auto res2 = m.emplace("one", "uno");
+    std::cout << std::boolalpha << "inserted: " << res2.second << ", value: " << res2.first->second << std::endl;
+}

docs/mkdocs/docs/examples/ordered_map__emplace.output

@@ -0,0 +1,2 @@
+inserted: true, value: eins
+inserted: false, value: eins

docs/mkdocs/docs/examples/ordered_map__erase.cpp

@@ -0,0 +1,24 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+    m["two"] = 2;
+    m["three"] = 3;
+
+    // erase by key
+    std::size_t removed = m.erase("two");
+    std::cout << "removed by key: " << removed << std::endl;
+
+    // erase by iterator
+    m.erase(m.begin());
+
+    std::cout << "remaining: ";
+    for (const auto& element : m)
+    {
+        std::cout << element.first << ' ';
+    }
+    std::cout << std::endl;
+}

docs/mkdocs/docs/examples/ordered_map__erase.output

@@ -0,0 +1,2 @@
+removed by key: 1
+remaining: three 

docs/mkdocs/docs/examples/ordered_map__find.cpp

@@ -0,0 +1,19 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+
+    auto it = m.find("one");
+    if (it != m.end())
+    {
+        std::cout << "found: " << it->first << " = " << it->second << std::endl;
+    }
+
+    if (m.find("two") == m.end())
+    {
+        std::cout << "\"two\" not found" << std::endl;
+    }
+}

docs/mkdocs/docs/examples/ordered_map__find.output

@@ -0,0 +1,2 @@
+found: one = 1
+"two" not found

docs/mkdocs/docs/examples/ordered_map__insert.cpp

@@ -0,0 +1,21 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+
+    // insert a single value
+    auto res = m.insert({"one", 1});
+    std::cout << std::boolalpha << "inserted: " << res.second << std::endl;
+
+    // insert a range from another container
+    std::vector<std::pair<const std::string, int>> more = {{"two", 2}, {"three", 3}};
+    m.insert(more.begin(), more.end());
+
+    for (const auto& element : m)
+    {
+        std::cout << element.first << ':' << element.second << ' ';
+    }
+    std::cout << std::endl;
+}

docs/mkdocs/docs/examples/ordered_map__insert.output

@@ -0,0 +1,2 @@
+inserted: true
+one:1 two:2 three:3 

docs/mkdocs/docs/examples/ordered_map__key_compare.cpp

@@ -0,0 +1,12 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    using Map = nlohmann::ordered_map<std::string, int>;
+    Map::key_compare compare{};
+
+    std::cout << std::boolalpha
+              << "compare(\"a\", \"a\") = " << compare("a", "a") << '\n'
+              << "compare(\"a\", \"b\") = " << compare("a", "b") << std::endl;
+}

docs/mkdocs/docs/examples/ordered_map__key_compare.output

@@ -0,0 +1,2 @@
+compare("a", "a") = true
+compare("a", "b") = false

docs/mkdocs/docs/examples/ordered_map__operator_idx.cpp

@@ -0,0 +1,14 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+
+    // operator[] inserts a default-constructed value if the key doesn't exist yet
+    m["one"] = 1;
+    std::cout << "m[\"one\"] = " << m["one"] << std::endl;
+
+    // accessing again just returns the existing value
+    std::cout << "m[\"one\"] = " << m["one"] << std::endl;
+}

docs/mkdocs/docs/examples/ordered_map__operator_idx.output

@@ -0,0 +1,2 @@
+m["one"] = 1
+m["one"] = 1

docs/mkdocs/docs/features/arbitrary_types.md

@@ -215,24 +215,6 @@ For _derived_ classes and structs, use the following macros
     nlohmann::ordered_json j = p; // keys appear in declaration order: name, address, age
     ```
 
-!!! note "Zero-member types"
-
-    All 12 `NLOHMANN_DEFINE_TYPE_*`/`NLOHMANN_DEFINE_DERIVED_TYPE_*` macros (excluding the `WITH_NAMES` variants)
-    also accept types with no member variables to serialize, producing/accepting an empty JSON object `{}`
-    (or, for the derived-type macros, just the base class's own JSON representation):
-
-    ```cpp
-    namespace ns {
-        struct marker {
-            bool operator==(const marker&) const { return true; }
-            NLOHMANN_DEFINE_TYPE_INTRUSIVE(marker)
-        };
-    }
-
-    ns::marker m{};
-    nlohmann::json j = m; // {}
-    ```
-
 !!! note "No macro for non-default-constructible types"
 
     There is currently no `NLOHMANN_DEFINE_TYPE_*`-style macro for types that are not

docs/mkdocs/docs/home/architecture.md

@@ -17,7 +17,7 @@ The main structure is class [nlohmann::basic_json](../api/basic_json/index.md).
 
 - describe template parameters of `basic_json`
 - [`json`](../api/json.md)
-- [`ordered_json`](../api/ordered_json.md) via [`ordered_map`](../api/ordered_map.md)
+- [`ordered_json`](../api/ordered_json.md) via [`ordered_map`](../api/ordered_map/index.md)
 
 ## Value storage
 

docs/mkdocs/docs/home/releases.md

@@ -2,7 +2,8 @@
 
 This page summarizes the notable changes of every release and links to the relevant documentation.
 The **complete release notes** — including all changes, the download files, and their checksums — are
-published on the [GitHub releases page](https://github.com/nlohmann/json/releases).
+published on the [GitHub releases page](https://github.com/nlohmann/json/releases). For a raw,
+signature-level diff of the public API between releases, see [API Changes](api_changes.md).
 
 ## v3.12.0 (2025-04-11)
 

docs/mkdocs/mkdocs.yml

@@ -52,6 +52,7 @@ nav:
       - "FAQ": home/faq.md
       - home/exceptions.md
       - home/releases.md
+      - home/api_changes.md
       - home/design_goals.md
       - home/architecture.md
       - home/customers.md
@@ -117,6 +118,7 @@ nav:
           - 'begin': api/basic_json/begin.md
           - 'binary': api/basic_json/binary.md
           - 'binary_t': api/basic_json/binary_t.md
+          - 'bjdata_version_t': api/basic_json/bjdata_version_t.md
           - 'boolean_t': api/basic_json/boolean_t.md
           - 'cbegin': api/basic_json/cbegin.md
           - 'cbor_tag_handler_t': api/basic_json/cbor_tag_handler_t.md
@@ -154,6 +156,7 @@ nav:
           - 'get_to': api/basic_json/get_to.md
           - 'std::formatter<basic_json>': api/basic_json/std_formatter.md
           - 'std::hash<basic_json>': api/basic_json/std_hash.md
+          - 'initializer_list_t': api/basic_json/initializer_list_t.md
           - 'input_format_t': api/basic_json/input_format_t.md
           - 'insert': api/basic_json/insert.md
           - 'invalid_iterator': api/basic_json/invalid_iterator.md
@@ -172,6 +175,7 @@ nav:
           - 'is_structured': api/basic_json/is_structured.md
           - 'items': api/basic_json/items.md
           - 'json_base_class_t': api/basic_json/json_base_class_t.md
+          - 'json_sax_t': api/basic_json/json_sax_t.md
           - 'json_serializer': api/basic_json/json_serializer.md
           - 'max_size': api/basic_json/max_size.md
           - 'meta': api/basic_json/meta.md
@@ -228,9 +232,13 @@ nav:
           - 'Overview': api/byte_container_with_subtype/index.md
           - '(constructor)': api/byte_container_with_subtype/byte_container_with_subtype.md
           - 'clear_subtype': api/byte_container_with_subtype/clear_subtype.md
+          - 'container_type': api/byte_container_with_subtype/container_type.md
           - 'has_subtype': api/byte_container_with_subtype/has_subtype.md
+          - 'operator==': api/byte_container_with_subtype/operator_eq.md
+          - 'operator!=': api/byte_container_with_subtype/operator_ne.md
           - 'set_subtype': api/byte_container_with_subtype/set_subtype.md
           - 'subtype': api/byte_container_with_subtype/subtype.md
+          - 'subtype_type': api/byte_container_with_subtype/subtype_type.md
       - adl_serializer:
           - 'Overview': api/adl_serializer/index.md
           - 'from_json': api/adl_serializer/from_json.md
@@ -256,25 +264,46 @@ nav:
           - 'to_string': api/json_pointer/to_string.md
       - json_sax:
           - 'Overview': api/json_sax/index.md
+          - '(Constructor)': api/json_sax/json_sax.md
+          - '(Destructor)': api/json_sax/~json_sax.md
+          - 'operator=': api/json_sax/operator=.md
           - 'binary': api/json_sax/binary.md
+          - 'binary_t': api/json_sax/binary_t.md
           - 'boolean': api/json_sax/boolean.md
           - 'end_array': api/json_sax/end_array.md
           - 'end_object': api/json_sax/end_object.md
           - 'key': api/json_sax/key.md
           - 'null': api/json_sax/null.md
           - 'number_float': api/json_sax/number_float.md
+          - 'number_float_t': api/json_sax/number_float_t.md
           - 'number_integer': api/json_sax/number_integer.md
+          - 'number_integer_t': api/json_sax/number_integer_t.md
           - 'number_unsigned': api/json_sax/number_unsigned.md
+          - 'number_unsigned_t': api/json_sax/number_unsigned_t.md
           - 'parse_error': api/json_sax/parse_error.md
           - 'start_array': api/json_sax/start_array.md
           - 'start_object': api/json_sax/start_object.md
           - 'string': api/json_sax/string.md
+          - 'string_t': api/json_sax/string_t.md
       - 'operator<<(basic_json), operator<<(json_pointer)': api/operator_ltlt.md
       - 'operator>>(basic_json)': api/operator_gtgt.md
       - 'operator""_json': api/operator_literal_json.md
       - 'operator""_json_pointer': api/operator_literal_json_pointer.md
       - 'ordered_json': api/ordered_json.md
-      - 'ordered_map': api/ordered_map.md
+      - ordered_map:
+          - 'Overview': api/ordered_map/index.md
+          - '(Constructor)': api/ordered_map/ordered_map.md
+          - '(Destructor)': api/ordered_map/~ordered_map.md
+          - 'operator=': api/ordered_map/operator=.md
+          - 'at': api/ordered_map/at.md
+          - 'Container': api/ordered_map/Container.md
+          - 'count': api/ordered_map/count.md
+          - 'emplace': api/ordered_map/emplace.md
+          - 'erase': api/ordered_map/erase.md
+          - 'find': api/ordered_map/find.md
+          - 'insert': api/ordered_map/insert.md
+          - 'key_compare': api/ordered_map/key_compare.md
+          - 'operator[]': api/ordered_map/operator[].md
       - macros:
           - 'Overview': api/macros/index.md
           - 'JSON_ASSERT': api/macros/json_assert.md

include/nlohmann/byte_container_with_subtype.hpp

@@ -22,7 +22,9 @@ template<typename BinaryType>
 class byte_container_with_subtype : public BinaryType
 {
   public:
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/container_type/
     using container_type = BinaryType;
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/subtype_type/
     using subtype_type = std::uint64_t;
 
     /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/byte_container_with_subtype/
@@ -54,12 +56,14 @@ class byte_container_with_subtype : public BinaryType
         , m_has_subtype(true)
     {}
 
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/operator_eq/
     bool operator==(const byte_container_with_subtype& rhs) const
     {
         return std::tie(static_cast<const BinaryType&>(*this), m_subtype, m_has_subtype) ==
                std::tie(static_cast<const BinaryType&>(rhs), rhs.m_subtype, rhs.m_has_subtype);
     }
 
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/operator_ne/
     bool operator!=(const byte_container_with_subtype& rhs) const
     {
         return !(rhs == *this);

include/nlohmann/detail/input/json_sax.hpp

@@ -31,15 +31,21 @@ input.
 template<typename BasicJsonType>
 struct json_sax
 {
+    /// @sa https://json.nlohmann.me/api/json_sax/number_integer_t/
     using number_integer_t = typename BasicJsonType::number_integer_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/number_unsigned_t/
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/number_float_t/
     using number_float_t = typename BasicJsonType::number_float_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/string_t/
     using string_t = typename BasicJsonType::string_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/binary_t/
     using binary_t = typename BasicJsonType::binary_t;
 
     /*!
     @brief a null value was read
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/null/
     */
     virtual bool null() = 0;
 
@@ -47,6 +53,7 @@ struct json_sax
     @brief a boolean value was read
     @param[in] val  boolean value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/boolean/
     */
     virtual bool boolean(bool val) = 0;
 
@@ -54,6 +61,7 @@ struct json_sax
     @brief an integer number was read
     @param[in] val  integer value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/number_integer/
     */
     virtual bool number_integer(number_integer_t val) = 0;
 
@@ -61,6 +69,7 @@ struct json_sax
     @brief an unsigned integer number was read
     @param[in] val  unsigned integer value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/number_unsigned/
     */
     virtual bool number_unsigned(number_unsigned_t val) = 0;
 
@@ -69,6 +78,7 @@ struct json_sax
     @param[in] val  floating-point value
     @param[in] s    raw token value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/number_float/
     */
     virtual bool number_float(number_float_t val, const string_t& s) = 0;
 
@@ -77,6 +87,7 @@ struct json_sax
     @param[in] val  string value
     @return whether parsing should proceed
     @note It is safe to move the passed string value.
+    @sa https://json.nlohmann.me/api/json_sax/string/
     */
     virtual bool string(string_t& val) = 0;
 
@@ -85,6 +96,7 @@ struct json_sax
     @param[in] val  binary value
     @return whether parsing should proceed
     @note It is safe to move the passed binary value.
+    @sa https://json.nlohmann.me/api/json_sax/binary/
     */
     virtual bool binary(binary_t& val) = 0;
 
@@ -93,6 +105,7 @@ struct json_sax
     @param[in] elements  number of object elements or -1 if unknown
     @return whether parsing should proceed
     @note binary formats may report the number of elements
+    @sa https://json.nlohmann.me/api/json_sax/start_object/
     */
     virtual bool start_object(std::size_t elements) = 0;
 
@@ -101,12 +114,14 @@ struct json_sax
     @param[in] val  object key
     @return whether parsing should proceed
     @note It is safe to move the passed string.
+    @sa https://json.nlohmann.me/api/json_sax/key/
     */
     virtual bool key(string_t& val) = 0;
 
     /*!
     @brief the end of an object was read
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/end_object/
     */
     virtual bool end_object() = 0;
 
@@ -115,12 +130,14 @@ struct json_sax
     @param[in] elements  number of array elements or -1 if unknown
     @return whether parsing should proceed
     @note binary formats may report the number of elements
+    @sa https://json.nlohmann.me/api/json_sax/start_array/
     */
     virtual bool start_array(std::size_t elements) = 0;
 
     /*!
     @brief the end of an array was read
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/end_array/
     */
     virtual bool end_array() = 0;
 
@@ -130,16 +147,23 @@ struct json_sax
     @param[in] last_token  the last read token
     @param[in] ex          an exception object describing the error
     @return whether parsing should proceed (must return false)
+    @sa https://json.nlohmann.me/api/json_sax/parse_error/
     */
     virtual bool parse_error(std::size_t position,
                              const std::string& last_token,
                              const detail::exception& ex) = 0;
 
+    /// @sa https://json.nlohmann.me/api/json_sax/json_sax/
     json_sax() = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/json_sax/
     json_sax(const json_sax&) = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/json_sax/
     json_sax(json_sax&&) noexcept = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/operator=/
     json_sax& operator=(const json_sax&) = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/operator=/
     json_sax& operator=(json_sax&&) noexcept = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/~json_sax/
     virtual ~json_sax() = default;
 };
 

include/nlohmann/detail/json_pointer.hpp

@@ -55,6 +55,7 @@ class json_pointer
 
   public:
     // for backwards compatibility accept BasicJsonType
+    /// @sa https://json.nlohmann.me/api/json_pointer/string_t/
     using string_t = typename string_t_helper<RefStringType>::type;
 
     /// @brief create JSON pointer

include/nlohmann/detail/macro_scope.hpp

@@ -587,59 +587,16 @@ void templated_json_throw(ExceptionType exception)
 
 #define NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0> __VA_ARGS__
 
-// Tags used to dispatch the NLOHMANN_DEFINE_TYPE_*/NLOHMANN_DEFINE_DERIVED_TYPE_*
-// macros below between a zero-member and a one-or-more-member implementation
-// (issue #4041, e.g. NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type) with no further
-// arguments). NLOHMANN_JSON_TYPE_TAG(...) expands to the token EMPTY when
-// __VA_ARGS__ is a single token (Type alone) and to MEMBERS for two or more
-// (Type, member...), naming the body the public macro dispatches to. It
-// reuses the existing 64-slot NLOHMANN_JSON_GET_MACRO dispatch with one extra
-// trailing sentinel token appended so its own trailing "..." is never left
-// completely empty at the lowest supported argument count --
-// invoking a variadic macro so that "..." matches nothing is only granted
-// unconditionally by the standard since C++20, and pre-C++20 compilers may
-// reject it under -pedantic regardless of what the macro body does.
-//
-// NLOHMANN_JSON_DERIVED_TYPE_TAG(...) answers the same question for the
-// derived-type macros, whose fixed prefix is Type,BaseType. It drops the
-// leading Type and defers to NLOHMANN_JSON_TYPE_TAG rather than shifting the
-// slot table by one: NLOHMANN_JSON_GET_MACRO only resolves 64 positional
-// arguments, so tagging Type,BaseType,member... directly would run out one
-// slot early and cap the derived-type macros at 62 members instead of the 63
-// that NLOHMANN_JSON_PASTE supports.
-#define NLOHMANN_JSON_CAT_(x, y) x ## y
-#define NLOHMANN_JSON_CAT(x, y) NLOHMANN_JSON_CAT_(x, y)
-
-#define NLOHMANN_JSON_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, EMPTY, \
-        NLOHMANN_JSON_TYPE_TAG_SENTINEL))
-
-#define NLOHMANN_JSON_DERIVED_TYPE_TAG_(Type, ...) NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__)
-#define NLOHMANN_JSON_DERIVED_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_TAG_(__VA_ARGS__))
-
 /*!
 @brief macro
 @def NLOHMANN_DEFINE_TYPE_INTRUSIVE
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
-
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -650,15 +607,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)
-
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -669,14 +621,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
-
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -686,17 +633,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
-
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -707,15 +647,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)
-
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -726,14 +661,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
-
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -743,17 +673,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -764,15 +687,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -783,14 +701,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -801,17 +714,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -822,15 +728,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -841,14 +742,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 

include/nlohmann/json.hpp

@@ -192,22 +192,31 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using serializer = ::nlohmann::detail::serializer<basic_json>;
 
   public:
+    /// @brief the type of the JSON value
+    /// @sa https://json.nlohmann.me/api/basic_json/value_t/
     using value_t = detail::value_t;
     /// JSON Pointer, see @ref nlohmann::json_pointer
     using json_pointer = ::nlohmann::json_pointer<StringType>;
     template<typename T, typename SFINAE>
     using json_serializer = JSONSerializer<T, SFINAE>;
     /// how to treat decoding errors
+    /// @sa https://json.nlohmann.me/api/basic_json/error_handler_t/
     using error_handler_t = detail::error_handler_t;
     /// how to treat CBOR tags
+    /// @sa https://json.nlohmann.me/api/basic_json/cbor_tag_handler_t/
     using cbor_tag_handler_t = detail::cbor_tag_handler_t;
     /// how to encode BJData
+    /// @sa https://json.nlohmann.me/api/basic_json/bjdata_version_t/
     using bjdata_version_t = detail::bjdata_version_t;
     /// helper type for initializer lists of basic_json values
+    /// @sa https://json.nlohmann.me/api/basic_json/initializer_list_t/
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
+    /// @brief the type of the SAX interface used to parse and serialize the JSON value
+    /// @sa https://json.nlohmann.me/api/basic_json/input_format_t/
     using input_format_t = detail::input_format_t;
     /// SAX interface type, see @ref nlohmann::json_sax
+    /// @sa https://json.nlohmann.me/api/basic_json/json_sax_t/
     using json_sax_t = json_sax<basic_json>;
 
     ////////////////
@@ -349,15 +358,19 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// the template arguments passed to class @ref basic_json.
     /// @{
 
+#if defined(JSON_HAS_CPP_14)
     /// @brief default object key comparator type
     /// The actual object key comparator type (@ref object_comparator_t) may be
     /// different.
     /// @sa https://json.nlohmann.me/api/basic_json/default_object_comparator_t/
-#if defined(JSON_HAS_CPP_14)
     // use of transparent comparator avoids unnecessary repeated construction of temporaries
     // in functions involving lookup by key with types other than object_t::key_type (aka. StringType)
     using default_object_comparator_t = std::less<>;
 #else
+    /// @brief default object key comparator type
+    /// The actual object key comparator type (@ref object_comparator_t) may be
+    /// different.
+    /// @sa https://json.nlohmann.me/api/basic_json/default_object_comparator_t/
     using default_object_comparator_t = std::less<StringType>;
 #endif
 
@@ -1182,6 +1195,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     // other constructors and destructor //
     ///////////////////////////////////////
 
+    /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     template<typename JsonRef,
              detail::enable_if_t<detail::conjunction<detail::is_json_ref<JsonRef>,
                                  std::is_same<typename JsonRef::value_type, basic_json>>::value, int> = 0 >
@@ -1802,6 +1816,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     @throw what @ref json_serializer<ValueType> `from_json()` method throws if conversion is required
 
     @since version 2.1.0
+
+    @sa https://json.nlohmann.me/api/basic_json/get/
     */
     template < typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>>
 #if defined(JSON_HAS_CPP_14)
@@ -1845,6 +1861,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     @sa see @ref get_ptr() for explicit pointer-member access
 
     @since version 1.0.0
+
+    @sa https://json.nlohmann.me/api/basic_json/get/
     */
     template<typename PointerType, typename std::enable_if<
                  std::is_pointer<PointerType>::value, int>::type = 0>
@@ -1870,6 +1888,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     // specialization to allow calling get_to with a basic_json value
     // see https://github.com/nlohmann/json/issues/2175
+    /// @sa https://json.nlohmann.me/api/basic_json/get_to/
     template<typename ValueType,
              detail::enable_if_t <
                  detail::is_basic_json<ValueType>::value,
@@ -1880,6 +1899,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return v;
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/get_to/
     template <
         typename T, std::size_t N,
         typename Array = T (&)[N], // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
@@ -1943,6 +1963,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     @since version 1.0.0
     */
+    /// @sa https://json.nlohmann.me/api/basic_json/operator_ValueType/
     template < typename ValueType, typename std::enable_if <
                    detail::conjunction <
                        detail::negation<std::is_pointer<ValueType>>,
@@ -2224,12 +2245,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     // these two functions resolve a (const) char * ambiguity affecting Clang and MSVC
     // (they seemingly cannot be constrained to resolve the ambiguity)
+    /// @sa https://json.nlohmann.me/api/basic_json/operator[]/
     template<typename T>
     reference operator[](T* key)
     {
         return operator[](typename object_t::key_type(key));
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/operator[]/
     template<typename T>
     const_reference operator[](T* key) const
     {
@@ -2439,6 +2462,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         JSON_THROW(type_error::create(306, detail::concat("cannot use value() with ", type_name()), this));
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/value/
     template < class ValueType, class BasicJsonType, detail::enable_if_t <
                    detail::is_basic_json<BasicJsonType>::value
                    && detail::is_getable<basic_json_t, ValueType>::value
@@ -2449,6 +2473,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return value(ptr.convert(), default_value);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/value/
     template < class ValueType, class BasicJsonType, class ReturnType = typename value_return_type<ValueType>::type,
                detail::enable_if_t <
                    detail::is_basic_json<BasicJsonType>::value
@@ -2818,6 +2843,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.contains(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/contains/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     bool contains(const typename ::nlohmann::json_pointer<BasicJsonType>& ptr) const
@@ -4100,6 +4126,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return result;
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/parse/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, parse(ptr, ptr + len))
     static basic_json parse(detail::span_input_adapter&& i,
@@ -4134,6 +4161,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/accept/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, accept(ptr, ptr + len))
     static bool accept(detail::span_input_adapter&& i,
@@ -4481,6 +4509,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_cbor/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_cbor(ptr, ptr + len))
@@ -4492,6 +4521,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_cbor(ptr, ptr + len, strict, allow_exceptions, tag_handler);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_cbor/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_cbor(ptr, ptr + len))
     static basic_json from_cbor(detail::span_input_adapter&& i,
@@ -4538,6 +4568,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_msgpack(ptr, ptr + len))
@@ -4548,6 +4579,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_msgpack(ptr, ptr + len, strict, allow_exceptions);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_msgpack(ptr, ptr + len))
     static basic_json from_msgpack(detail::span_input_adapter&& i,
@@ -4593,6 +4625,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_ubjson(ptr, ptr + len))
@@ -4603,6 +4636,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_ubjson(ptr, ptr + len, strict, allow_exceptions);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_ubjson(ptr, ptr + len))
     static basic_json from_ubjson(detail::span_input_adapter&& i,
@@ -4679,6 +4713,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_bson(ptr, ptr + len))
@@ -4689,6 +4724,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_bson(ptr, ptr + len, strict, allow_exceptions);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_bson(ptr, ptr + len))
     static basic_json from_bson(detail::span_input_adapter&& i,
@@ -4718,6 +4754,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_unchecked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/operator%5B%5D/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     reference operator[](const ::nlohmann::json_pointer<BasicJsonType>& ptr)
@@ -4732,6 +4769,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_unchecked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/operator%5B%5D/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     const_reference operator[](const ::nlohmann::json_pointer<BasicJsonType>& ptr) const
@@ -4746,6 +4784,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_checked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/at/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     reference at(const ::nlohmann::json_pointer<BasicJsonType>& ptr)
@@ -4760,6 +4799,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_checked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/at/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     const_reference at(const ::nlohmann::json_pointer<BasicJsonType>& ptr) const

include/nlohmann/ordered_map.hpp

@@ -30,30 +30,41 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
 {
     using key_type = Key;
     using mapped_type = T;
+    /// @sa https://json.nlohmann.me/api/ordered_map/Container/
     using Container = std::vector<std::pair<const Key, T>, Allocator>;
     using iterator = typename Container::iterator;
     using const_iterator = typename Container::const_iterator;
     using size_type = typename Container::size_type;
     using value_type = typename Container::value_type;
 #ifdef JSON_HAS_CPP_14
+    /// @sa https://json.nlohmann.me/api/ordered_map/key_compare/
     using key_compare = std::equal_to<>;
 #else
+    /// @sa https://json.nlohmann.me/api/ordered_map/key_compare/
     using key_compare = std::equal_to<Key>;
 #endif
 
     // Explicit constructors instead of `using Container::Container`
     // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map() noexcept(noexcept(Container())) : Container{} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     explicit ordered_map(const Allocator& alloc) noexcept(noexcept(Container(alloc))) : Container{alloc} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     template <class It>
     ordered_map(It first, It last, const Allocator& alloc = Allocator())
         : Container{first, last, alloc} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map(std::initializer_list<value_type> init, const Allocator& alloc = Allocator() )
         : Container{init, alloc} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map(const ordered_map&) = default;
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map(ordered_map&&) noexcept(std::is_nothrow_move_constructible<Container>::value) = default;
+    /// @sa https://json.nlohmann.me/api/ordered_map/~ordered_map/
     ~ordered_map() = default;
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator=/
     ordered_map& operator=(const ordered_map& other)
     {
         if (this != &other)
@@ -64,12 +75,14 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return *this;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator=/
     ordered_map& operator=(ordered_map&& other) noexcept(std::is_nothrow_move_assignable<Container>::value)
     {
         Container::operator=(std::move(static_cast<Container&>(other)));
         return *this;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/emplace/
     std::pair<iterator, bool> emplace(const key_type& key, T&& t)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -83,6 +96,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return {std::prev(this->end()), true};
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/emplace/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     std::pair<iterator, bool> emplace(KeyType && key, T && t)
@@ -98,11 +112,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return {std::prev(this->end()), true};
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     T& operator[](const key_type& key)
     {
         return emplace(key, T{}).first->second;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     T & operator[](KeyType && key)
@@ -110,11 +126,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return emplace(std::forward<KeyType>(key), T{}).first->second;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     const T& operator[](const key_type& key) const
     {
         return at(key);
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     const T & operator[](KeyType && key) const
@@ -122,6 +140,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return at(std::forward<KeyType>(key));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     T& at(const key_type& key)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -135,6 +154,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     T & at(KeyType && key) // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -150,6 +170,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     const T& at(const key_type& key) const
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -163,6 +184,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     const T & at(KeyType && key) const // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -178,6 +200,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     size_type erase(const key_type& key)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -197,6 +220,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     size_type erase(KeyType && key) // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -218,11 +242,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     iterator erase(iterator pos)
     {
         return erase(pos, std::next(pos));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     iterator erase(iterator first, iterator last)
     {
         if (first == last)
@@ -276,6 +302,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::begin() + offset;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/count/
     size_type count(const key_type& key) const
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -288,6 +315,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/count/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     size_type count(KeyType && key) const // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -302,6 +330,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     iterator find(const key_type& key)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -314,6 +343,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     iterator find(KeyType && key) // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -328,6 +358,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     const_iterator find(const key_type& key) const
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -340,6 +371,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     const_iterator find(KeyType && key) const // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -354,11 +386,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/insert/
     std::pair<iterator, bool> insert( value_type&& value )
     {
         return emplace(value.first, std::move(value.second));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/insert/
     std::pair<iterator, bool> insert( const value_type& value )
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -376,6 +410,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
     using require_input_iter = typename std::enable_if<std::is_convertible<typename std::iterator_traits<InputIt>::iterator_category,
         std::input_iterator_tag>::value>::type;
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/insert/
     template<typename InputIt, typename = require_input_iter<InputIt>>
     void insert(InputIt first, InputIt last)
     {

single_include/nlohmann/json.hpp

@@ -2962,59 +2962,16 @@ void templated_json_throw(ExceptionType exception)
 
 #define NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0> __VA_ARGS__
 
-// Tags used to dispatch the NLOHMANN_DEFINE_TYPE_*/NLOHMANN_DEFINE_DERIVED_TYPE_*
-// macros below between a zero-member and a one-or-more-member implementation
-// (issue #4041, e.g. NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type) with no further
-// arguments). NLOHMANN_JSON_TYPE_TAG(...) expands to the token EMPTY when
-// __VA_ARGS__ is a single token (Type alone) and to MEMBERS for two or more
-// (Type, member...), naming the body the public macro dispatches to. It
-// reuses the existing 64-slot NLOHMANN_JSON_GET_MACRO dispatch with one extra
-// trailing sentinel token appended so its own trailing "..." is never left
-// completely empty at the lowest supported argument count --
-// invoking a variadic macro so that "..." matches nothing is only granted
-// unconditionally by the standard since C++20, and pre-C++20 compilers may
-// reject it under -pedantic regardless of what the macro body does.
-//
-// NLOHMANN_JSON_DERIVED_TYPE_TAG(...) answers the same question for the
-// derived-type macros, whose fixed prefix is Type,BaseType. It drops the
-// leading Type and defers to NLOHMANN_JSON_TYPE_TAG rather than shifting the
-// slot table by one: NLOHMANN_JSON_GET_MACRO only resolves 64 positional
-// arguments, so tagging Type,BaseType,member... directly would run out one
-// slot early and cap the derived-type macros at 62 members instead of the 63
-// that NLOHMANN_JSON_PASTE supports.
-#define NLOHMANN_JSON_CAT_(x, y) x ## y
-#define NLOHMANN_JSON_CAT(x, y) NLOHMANN_JSON_CAT_(x, y)
-
-#define NLOHMANN_JSON_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
-        MEMBERS, MEMBERS, MEMBERS, EMPTY, \
-        NLOHMANN_JSON_TYPE_TAG_SENTINEL))
-
-#define NLOHMANN_JSON_DERIVED_TYPE_TAG_(Type, ...) NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__)
-#define NLOHMANN_JSON_DERIVED_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_TAG_(__VA_ARGS__))
-
 /*!
 @brief macro
 @def NLOHMANN_DEFINE_TYPE_INTRUSIVE
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
-
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -3025,15 +2982,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)
-
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -3044,14 +2996,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
-
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -3061,17 +3008,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
-
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -3082,15 +3022,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)
-
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -3101,14 +3036,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, ...)  \
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
-
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -3118,17 +3048,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -3139,15 +3062,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -3158,14 +3076,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -3176,17 +3089,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
-    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -3197,15 +3103,10 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
-// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -3216,14 +3117,9 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_MEMBERS(Type, BaseType, ...)  \
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
-#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_EMPTY(Type, BaseType)  \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
-
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
-
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -6836,7 +6732,9 @@ template<typename BinaryType>
 class byte_container_with_subtype : public BinaryType
 {
   public:
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/container_type/
     using container_type = BinaryType;
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/subtype_type/
     using subtype_type = std::uint64_t;
 
     /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/byte_container_with_subtype/
@@ -6868,12 +6766,14 @@ class byte_container_with_subtype : public BinaryType
         , m_has_subtype(true)
     {}
 
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/operator_eq/
     bool operator==(const byte_container_with_subtype& rhs) const
     {
         return std::tie(static_cast<const BinaryType&>(*this), m_subtype, m_has_subtype) ==
                std::tie(static_cast<const BinaryType&>(rhs), rhs.m_subtype, rhs.m_has_subtype);
     }
 
+    /// @sa https://json.nlohmann.me/api/byte_container_with_subtype/operator_ne/
     bool operator!=(const byte_container_with_subtype& rhs) const
     {
         return !(rhs == *this);
@@ -9536,15 +9436,21 @@ input.
 template<typename BasicJsonType>
 struct json_sax
 {
+    /// @sa https://json.nlohmann.me/api/json_sax/number_integer_t/
     using number_integer_t = typename BasicJsonType::number_integer_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/number_unsigned_t/
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/number_float_t/
     using number_float_t = typename BasicJsonType::number_float_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/string_t/
     using string_t = typename BasicJsonType::string_t;
+    /// @sa https://json.nlohmann.me/api/json_sax/binary_t/
     using binary_t = typename BasicJsonType::binary_t;
 
     /*!
     @brief a null value was read
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/null/
     */
     virtual bool null() = 0;
 
@@ -9552,6 +9458,7 @@ struct json_sax
     @brief a boolean value was read
     @param[in] val  boolean value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/boolean/
     */
     virtual bool boolean(bool val) = 0;
 
@@ -9559,6 +9466,7 @@ struct json_sax
     @brief an integer number was read
     @param[in] val  integer value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/number_integer/
     */
     virtual bool number_integer(number_integer_t val) = 0;
 
@@ -9566,6 +9474,7 @@ struct json_sax
     @brief an unsigned integer number was read
     @param[in] val  unsigned integer value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/number_unsigned/
     */
     virtual bool number_unsigned(number_unsigned_t val) = 0;
 
@@ -9574,6 +9483,7 @@ struct json_sax
     @param[in] val  floating-point value
     @param[in] s    raw token value
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/number_float/
     */
     virtual bool number_float(number_float_t val, const string_t& s) = 0;
 
@@ -9582,6 +9492,7 @@ struct json_sax
     @param[in] val  string value
     @return whether parsing should proceed
     @note It is safe to move the passed string value.
+    @sa https://json.nlohmann.me/api/json_sax/string/
     */
     virtual bool string(string_t& val) = 0;
 
@@ -9590,6 +9501,7 @@ struct json_sax
     @param[in] val  binary value
     @return whether parsing should proceed
     @note It is safe to move the passed binary value.
+    @sa https://json.nlohmann.me/api/json_sax/binary/
     */
     virtual bool binary(binary_t& val) = 0;
 
@@ -9598,6 +9510,7 @@ struct json_sax
     @param[in] elements  number of object elements or -1 if unknown
     @return whether parsing should proceed
     @note binary formats may report the number of elements
+    @sa https://json.nlohmann.me/api/json_sax/start_object/
     */
     virtual bool start_object(std::size_t elements) = 0;
 
@@ -9606,12 +9519,14 @@ struct json_sax
     @param[in] val  object key
     @return whether parsing should proceed
     @note It is safe to move the passed string.
+    @sa https://json.nlohmann.me/api/json_sax/key/
     */
     virtual bool key(string_t& val) = 0;
 
     /*!
     @brief the end of an object was read
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/end_object/
     */
     virtual bool end_object() = 0;
 
@@ -9620,12 +9535,14 @@ struct json_sax
     @param[in] elements  number of array elements or -1 if unknown
     @return whether parsing should proceed
     @note binary formats may report the number of elements
+    @sa https://json.nlohmann.me/api/json_sax/start_array/
     */
     virtual bool start_array(std::size_t elements) = 0;
 
     /*!
     @brief the end of an array was read
     @return whether parsing should proceed
+    @sa https://json.nlohmann.me/api/json_sax/end_array/
     */
     virtual bool end_array() = 0;
 
@@ -9635,16 +9552,23 @@ struct json_sax
     @param[in] last_token  the last read token
     @param[in] ex          an exception object describing the error
     @return whether parsing should proceed (must return false)
+    @sa https://json.nlohmann.me/api/json_sax/parse_error/
     */
     virtual bool parse_error(std::size_t position,
                              const std::string& last_token,
                              const detail::exception& ex) = 0;
 
+    /// @sa https://json.nlohmann.me/api/json_sax/json_sax/
     json_sax() = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/json_sax/
     json_sax(const json_sax&) = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/json_sax/
     json_sax(json_sax&&) noexcept = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/operator=/
     json_sax& operator=(const json_sax&) = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/operator=/
     json_sax& operator=(json_sax&&) noexcept = default;
+    /// @sa https://json.nlohmann.me/api/json_sax/~json_sax/
     virtual ~json_sax() = default;
 };
 
@@ -15499,6 +15423,7 @@ class json_pointer
 
   public:
     // for backwards compatibility accept BasicJsonType
+    /// @sa https://json.nlohmann.me/api/json_pointer/string_t/
     using string_t = typename string_t_helper<RefStringType>::type;
 
     /// @brief create JSON pointer
@@ -20861,30 +20786,41 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
 {
     using key_type = Key;
     using mapped_type = T;
+    /// @sa https://json.nlohmann.me/api/ordered_map/Container/
     using Container = std::vector<std::pair<const Key, T>, Allocator>;
     using iterator = typename Container::iterator;
     using const_iterator = typename Container::const_iterator;
     using size_type = typename Container::size_type;
     using value_type = typename Container::value_type;
 #ifdef JSON_HAS_CPP_14
+    /// @sa https://json.nlohmann.me/api/ordered_map/key_compare/
     using key_compare = std::equal_to<>;
 #else
+    /// @sa https://json.nlohmann.me/api/ordered_map/key_compare/
     using key_compare = std::equal_to<Key>;
 #endif
 
     // Explicit constructors instead of `using Container::Container`
     // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map() noexcept(noexcept(Container())) : Container{} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     explicit ordered_map(const Allocator& alloc) noexcept(noexcept(Container(alloc))) : Container{alloc} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     template <class It>
     ordered_map(It first, It last, const Allocator& alloc = Allocator())
         : Container{first, last, alloc} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map(std::initializer_list<value_type> init, const Allocator& alloc = Allocator() )
         : Container{init, alloc} {}
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map(const ordered_map&) = default;
+    /// @sa https://json.nlohmann.me/api/ordered_map/ordered_map/
     ordered_map(ordered_map&&) noexcept(std::is_nothrow_move_constructible<Container>::value) = default;
+    /// @sa https://json.nlohmann.me/api/ordered_map/~ordered_map/
     ~ordered_map() = default;
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator=/
     ordered_map& operator=(const ordered_map& other)
     {
         if (this != &other)
@@ -20895,12 +20831,14 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return *this;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator=/
     ordered_map& operator=(ordered_map&& other) noexcept(std::is_nothrow_move_assignable<Container>::value)
     {
         Container::operator=(std::move(static_cast<Container&>(other)));
         return *this;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/emplace/
     std::pair<iterator, bool> emplace(const key_type& key, T&& t)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -20914,6 +20852,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return {std::prev(this->end()), true};
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/emplace/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     std::pair<iterator, bool> emplace(KeyType && key, T && t)
@@ -20929,11 +20868,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return {std::prev(this->end()), true};
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     T& operator[](const key_type& key)
     {
         return emplace(key, T{}).first->second;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     T & operator[](KeyType && key)
@@ -20941,11 +20882,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return emplace(std::forward<KeyType>(key), T{}).first->second;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     const T& operator[](const key_type& key) const
     {
         return at(key);
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/operator[]/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     const T & operator[](KeyType && key) const
@@ -20953,6 +20896,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return at(std::forward<KeyType>(key));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     T& at(const key_type& key)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -20966,6 +20910,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     T & at(KeyType && key) // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -20981,6 +20926,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     const T& at(const key_type& key) const
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -20994,6 +20940,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/at/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     const T & at(KeyType && key) const // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -21009,6 +20956,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         JSON_THROW(std::out_of_range("key not found"));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     size_type erase(const key_type& key)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -21028,6 +20976,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     size_type erase(KeyType && key) // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -21049,11 +20998,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     iterator erase(iterator pos)
     {
         return erase(pos, std::next(pos));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/erase/
     iterator erase(iterator first, iterator last)
     {
         if (first == last)
@@ -21107,6 +21058,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::begin() + offset;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/count/
     size_type count(const key_type& key) const
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -21119,6 +21071,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/count/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     size_type count(KeyType && key) const // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -21133,6 +21086,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return 0;
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     iterator find(const key_type& key)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -21145,6 +21099,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     iterator find(KeyType && key) // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -21159,6 +21114,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     const_iterator find(const key_type& key) const
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -21171,6 +21127,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/find/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     const_iterator find(KeyType && key) const // NOLINT(cppcoreguidelines-missing-std-forward)
@@ -21185,11 +21142,13 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return Container::end();
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/insert/
     std::pair<iterator, bool> insert( value_type&& value )
     {
         return emplace(value.first, std::move(value.second));
     }
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/insert/
     std::pair<iterator, bool> insert( const value_type& value )
     {
         for (auto it = this->begin(); it != this->end(); ++it)
@@ -21207,6 +21166,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
     using require_input_iter = typename std::enable_if<std::is_convertible<typename std::iterator_traits<InputIt>::iterator_category,
         std::input_iterator_tag>::value>::type;
 
+    /// @sa https://json.nlohmann.me/api/ordered_map/insert/
     template<typename InputIt, typename = require_input_iter<InputIt>>
     void insert(InputIt first, InputIt last)
     {
@@ -21343,22 +21303,31 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using serializer = ::nlohmann::detail::serializer<basic_json>;
 
   public:
+    /// @brief the type of the JSON value
+    /// @sa https://json.nlohmann.me/api/basic_json/value_t/
     using value_t = detail::value_t;
     /// JSON Pointer, see @ref nlohmann::json_pointer
     using json_pointer = ::nlohmann::json_pointer<StringType>;
     template<typename T, typename SFINAE>
     using json_serializer = JSONSerializer<T, SFINAE>;
     /// how to treat decoding errors
+    /// @sa https://json.nlohmann.me/api/basic_json/error_handler_t/
     using error_handler_t = detail::error_handler_t;
     /// how to treat CBOR tags
+    /// @sa https://json.nlohmann.me/api/basic_json/cbor_tag_handler_t/
     using cbor_tag_handler_t = detail::cbor_tag_handler_t;
     /// how to encode BJData
+    /// @sa https://json.nlohmann.me/api/basic_json/bjdata_version_t/
     using bjdata_version_t = detail::bjdata_version_t;
     /// helper type for initializer lists of basic_json values
+    /// @sa https://json.nlohmann.me/api/basic_json/initializer_list_t/
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
+    /// @brief the type of the SAX interface used to parse and serialize the JSON value
+    /// @sa https://json.nlohmann.me/api/basic_json/input_format_t/
     using input_format_t = detail::input_format_t;
     /// SAX interface type, see @ref nlohmann::json_sax
+    /// @sa https://json.nlohmann.me/api/basic_json/json_sax_t/
     using json_sax_t = json_sax<basic_json>;
 
     ////////////////
@@ -21500,15 +21469,19 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// the template arguments passed to class @ref basic_json.
     /// @{
 
+#if defined(JSON_HAS_CPP_14)
     /// @brief default object key comparator type
     /// The actual object key comparator type (@ref object_comparator_t) may be
     /// different.
     /// @sa https://json.nlohmann.me/api/basic_json/default_object_comparator_t/
-#if defined(JSON_HAS_CPP_14)
     // use of transparent comparator avoids unnecessary repeated construction of temporaries
     // in functions involving lookup by key with types other than object_t::key_type (aka. StringType)
     using default_object_comparator_t = std::less<>;
 #else
+    /// @brief default object key comparator type
+    /// The actual object key comparator type (@ref object_comparator_t) may be
+    /// different.
+    /// @sa https://json.nlohmann.me/api/basic_json/default_object_comparator_t/
     using default_object_comparator_t = std::less<StringType>;
 #endif
 
@@ -22333,6 +22306,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     // other constructors and destructor //
     ///////////////////////////////////////
 
+    /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     template<typename JsonRef,
              detail::enable_if_t<detail::conjunction<detail::is_json_ref<JsonRef>,
                                  std::is_same<typename JsonRef::value_type, basic_json>>::value, int> = 0 >
@@ -22953,6 +22927,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     @throw what @ref json_serializer<ValueType> `from_json()` method throws if conversion is required
 
     @since version 2.1.0
+
+    @sa https://json.nlohmann.me/api/basic_json/get/
     */
     template < typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>>
 #if defined(JSON_HAS_CPP_14)
@@ -22996,6 +22972,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     @sa see @ref get_ptr() for explicit pointer-member access
 
     @since version 1.0.0
+
+    @sa https://json.nlohmann.me/api/basic_json/get/
     */
     template<typename PointerType, typename std::enable_if<
                  std::is_pointer<PointerType>::value, int>::type = 0>
@@ -23021,6 +22999,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     // specialization to allow calling get_to with a basic_json value
     // see https://github.com/nlohmann/json/issues/2175
+    /// @sa https://json.nlohmann.me/api/basic_json/get_to/
     template<typename ValueType,
              detail::enable_if_t <
                  detail::is_basic_json<ValueType>::value,
@@ -23031,6 +23010,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return v;
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/get_to/
     template <
         typename T, std::size_t N,
         typename Array = T (&)[N], // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
@@ -23094,6 +23074,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     @since version 1.0.0
     */
+    /// @sa https://json.nlohmann.me/api/basic_json/operator_ValueType/
     template < typename ValueType, typename std::enable_if <
                    detail::conjunction <
                        detail::negation<std::is_pointer<ValueType>>,
@@ -23375,12 +23356,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     // these two functions resolve a (const) char * ambiguity affecting Clang and MSVC
     // (they seemingly cannot be constrained to resolve the ambiguity)
+    /// @sa https://json.nlohmann.me/api/basic_json/operator[]/
     template<typename T>
     reference operator[](T* key)
     {
         return operator[](typename object_t::key_type(key));
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/operator[]/
     template<typename T>
     const_reference operator[](T* key) const
     {
@@ -23590,6 +23573,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         JSON_THROW(type_error::create(306, detail::concat("cannot use value() with ", type_name()), this));
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/value/
     template < class ValueType, class BasicJsonType, detail::enable_if_t <
                    detail::is_basic_json<BasicJsonType>::value
                    && detail::is_getable<basic_json_t, ValueType>::value
@@ -23600,6 +23584,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return value(ptr.convert(), default_value);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/value/
     template < class ValueType, class BasicJsonType, class ReturnType = typename value_return_type<ValueType>::type,
                detail::enable_if_t <
                    detail::is_basic_json<BasicJsonType>::value
@@ -23969,6 +23954,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.contains(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/contains/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     bool contains(const typename ::nlohmann::json_pointer<BasicJsonType>& ptr) const
@@ -25251,6 +25237,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return result;
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/parse/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, parse(ptr, ptr + len))
     static basic_json parse(detail::span_input_adapter&& i,
@@ -25285,6 +25272,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/accept/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, accept(ptr, ptr + len))
     static bool accept(detail::span_input_adapter&& i,
@@ -25632,6 +25620,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_cbor/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_cbor(ptr, ptr + len))
@@ -25643,6 +25632,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_cbor(ptr, ptr + len, strict, allow_exceptions, tag_handler);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_cbor/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_cbor(ptr, ptr + len))
     static basic_json from_cbor(detail::span_input_adapter&& i,
@@ -25689,6 +25679,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_msgpack(ptr, ptr + len))
@@ -25699,6 +25690,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_msgpack(ptr, ptr + len, strict, allow_exceptions);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_msgpack(ptr, ptr + len))
     static basic_json from_msgpack(detail::span_input_adapter&& i,
@@ -25744,6 +25736,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_ubjson(ptr, ptr + len))
@@ -25754,6 +25747,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_ubjson(ptr, ptr + len, strict, allow_exceptions);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_ubjson(ptr, ptr + len))
     static basic_json from_ubjson(detail::span_input_adapter&& i,
@@ -25830,6 +25824,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
     template<typename T>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_bson(ptr, ptr + len))
@@ -25840,6 +25835,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return from_bson(ptr, ptr + len, strict, allow_exceptions);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_bson(ptr, ptr + len))
     static basic_json from_bson(detail::span_input_adapter&& i,
@@ -25869,6 +25865,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_unchecked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/operator%5B%5D/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     reference operator[](const ::nlohmann::json_pointer<BasicJsonType>& ptr)
@@ -25883,6 +25880,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_unchecked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/operator%5B%5D/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     const_reference operator[](const ::nlohmann::json_pointer<BasicJsonType>& ptr) const
@@ -25897,6 +25895,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_checked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/at/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     reference at(const ::nlohmann::json_pointer<BasicJsonType>& ptr)
@@ -25911,6 +25910,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return ptr.get_checked(this);
     }
 
+    /// @sa https://json.nlohmann.me/api/basic_json/at/
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     const_reference at(const ::nlohmann::json_pointer<BasicJsonType>& ptr) const

tests/src/unit-udt_macro.cpp

@@ -778,154 +778,6 @@ class derived_person_only_serialize_private_3 : person_without_default_construct
     NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(derived_person_only_serialize_private_3, person_without_default_constructor_3, "json_hair_color", hair_color)
 };
 
-// Zero-member types for issue #4041: NLOHMANN_DEFINE_TYPE_* and
-// NLOHMANN_DEFINE_DERIVED_TYPE_* must compile and produce a valid (empty)
-// JSON object when no member arguments are given.
-class empty_intrusive
-{
-  public:
-    bool operator==(const empty_intrusive& /*rhs*/) const
-    {
-        return true;
-    }
-    NLOHMANN_DEFINE_TYPE_INTRUSIVE(empty_intrusive)
-};
-
-class empty_intrusive_with_default
-{
-  public:
-    bool operator==(const empty_intrusive_with_default& /*rhs*/) const
-    {
-        return true;
-    }
-    NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(empty_intrusive_with_default)
-};
-
-class empty_intrusive_only_serialize
-{
-  public:
-    NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(empty_intrusive_only_serialize)
-};
-
-class empty_non_intrusive
-{
-  public:
-    bool operator==(const empty_non_intrusive& /*rhs*/) const
-    {
-        return true;
-    }
-};
-// NOLINTNEXTLINE(misc-use-internal-linkage)
-NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(empty_non_intrusive)
-
-class empty_non_intrusive_with_default
-{
-  public:
-    bool operator==(const empty_non_intrusive_with_default& /*rhs*/) const
-    {
-        return true;
-    }
-};
-// NOLINTNEXTLINE(misc-use-internal-linkage)
-NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(empty_non_intrusive_with_default)
-
-class empty_non_intrusive_only_serialize {};
-// NOLINTNEXTLINE(misc-use-internal-linkage)
-NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(empty_non_intrusive_only_serialize)
-
-class empty_derived_intrusive : public person_with_private_data
-{
-  public:
-    empty_derived_intrusive() = default;
-    empty_derived_intrusive(std::string name_, int age_, json metadata_)
-        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
-    {}
-    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(empty_derived_intrusive, person_with_private_data)
-};
-
-class empty_derived_intrusive_with_default : public person_with_private_data
-{
-  public:
-    empty_derived_intrusive_with_default() = default;
-    empty_derived_intrusive_with_default(std::string name_, int age_, json metadata_)
-        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
-    {}
-    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(empty_derived_intrusive_with_default, person_with_private_data)
-};
-
-class empty_derived_intrusive_only_serialize : public person_with_private_data
-{
-  public:
-    empty_derived_intrusive_only_serialize() = default;
-    empty_derived_intrusive_only_serialize(std::string name_, int age_, json metadata_)
-        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
-    {}
-    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(empty_derived_intrusive_only_serialize, person_with_private_data)
-};
-
-class empty_derived_non_intrusive : public person_with_private_data
-{
-  public:
-    empty_derived_non_intrusive() = default;
-    empty_derived_non_intrusive(std::string name_, int age_, json metadata_)
-        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
-    {}
-};
-// NOLINTNEXTLINE(misc-use-internal-linkage)
-NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(empty_derived_non_intrusive, person_with_private_data)
-
-class empty_derived_non_intrusive_with_default : public person_with_private_data
-{
-  public:
-    empty_derived_non_intrusive_with_default() = default;
-    empty_derived_non_intrusive_with_default(std::string name_, int age_, json metadata_)
-        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
-    {}
-};
-// NOLINTNEXTLINE(misc-use-internal-linkage)
-NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(empty_derived_non_intrusive_with_default, person_with_private_data)
-
-class empty_derived_non_intrusive_only_serialize : public person_with_private_data
-{
-  public:
-    empty_derived_non_intrusive_only_serialize() = default;
-    empty_derived_non_intrusive_only_serialize(std::string name_, int age_, json metadata_)
-        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
-    {}
-};
-// NOLINTNEXTLINE(misc-use-internal-linkage)
-NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(empty_derived_non_intrusive_only_serialize, person_with_private_data)
-
-// Types at the documented maximum member count (63) for issue #4041's
-// argument-count dispatch. The derived-type macros carry a two-token
-// Type,BaseType prefix, so they reach two slots further into
-// NLOHMANN_JSON_GET_MACRO than the non-derived ones and are the first to break
-// if the tag dispatch runs out of positional slots.
-class max_members
-{
-  public:
-    int m1{}, m2{}, m3{}, m4{}, m5{}, m6{}, m7{}, m8{}, m9{}, m10{}, m11{}, m12{}, m13{}, m14{}, m15{}, m16{}, m17{}, m18{}, m19{}, m20{}, m21{}, m22{}, m23{}, m24{}, m25{}, m26{}, m27{}, m28{}, m29{}, m30{}, m31{}, m32{}, m33{}, m34{}, m35{}, m36{}, m37{}, m38{}, m39{}, m40{}, m41{}, m42{}, m43{}, m44{}, m45{}, m46{}, m47{}, m48{}, m49{}, m50{}, m51{}, m52{}, m53{}, m54{}, m55{}, m56{}, m57{}, m58{}, m59{}, m60{}, m61{}, m62{}, m63{};
-
-    NLOHMANN_DEFINE_TYPE_INTRUSIVE(max_members, m1, m2, m3, m4, m5, m6, m7, m8, m9, m10, m11, m12, m13, m14, m15, m16, m17, m18, m19, m20, m21, m22, m23, m24, m25, m26, m27, m28, m29, m30, m31, m32, m33, m34, m35, m36, m37, m38, m39, m40, m41, m42, m43, m44, m45, m46, m47, m48, m49, m50, m51, m52, m53, m54, m55, m56, m57, m58, m59, m60, m61, m62, m63)
-};
-
-class max_members_base
-{
-  public:
-    int base_value = 0;
-
-    NLOHMANN_DEFINE_TYPE_INTRUSIVE(max_members_base, base_value)
-};
-
-class max_members_derived : public max_members_base
-{
-  public:
-    int m1{}, m2{}, m3{}, m4{}, m5{}, m6{}, m7{}, m8{}, m9{}, m10{}, m11{}, m12{}, m13{}, m14{}, m15{}, m16{}, m17{}, m18{}, m19{}, m20{}, m21{}, m22{}, m23{}, m24{}, m25{}, m26{}, m27{}, m28{}, m29{}, m30{}, m31{}, m32{}, m33{}, m34{}, m35{}, m36{}, m37{}, m38{}, m39{}, m40{}, m41{}, m42{}, m43{}, m44{}, m45{}, m46{}, m47{}, m48{}, m49{}, m50{}, m51{}, m52{}, m53{}, m54{}, m55{}, m56{}, m57{}, m58{}, m59{}, m60{}, m61{}, m62{}, m63{};
-
-    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(max_members_derived, max_members_base, m1, m2, m3, m4, m5, m6, m7, m8, m9, m10, m11, m12, m13, m14, m15, m16, m17, m18, m19, m20, m21, m22, m23, m24, m25, m26, m27, m28, m29, m30, m31, m32, m33, m34, m35, m36, m37, m38, m39, m40, m41, m42, m43, m44, m45, m46, m47, m48, m49, m50, m51, m52, m53, m54, m55, m56, m57, m58, m59, m60, m61, m62, m63)
-};
-
-
 } // namespace persons
 
 TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", Pair, // NOLINT(readability-math-missing-parentheses, bugprone-throwing-static-initialization)
@@ -1339,141 +1191,3 @@ TEST_CASE_TEMPLATE("Serialization of non-default-constructible classes via NLOHM
         }
     }
 }
-
-// Regression tests for issue #4041: NLOHMANN_DEFINE_TYPE_* and
-// NLOHMANN_DEFINE_DERIVED_TYPE_* macros must compile and produce valid
-// (empty, or base-only for the derived case) JSON objects when no member
-// arguments are given, on every supported C++ standard.
-TEST_CASE_TEMPLATE("Serialization/deserialization of zero-member types via NLOHMANN_DEFINE_TYPE_* (issue #4041)", Json, // NOLINT(readability-math-missing-parentheses, bugprone-throwing-static-initialization)
-                   nlohmann::json, nlohmann::ordered_json)
-{
-    constexpr bool is_ordered = std::is_same<Json, nlohmann::ordered_json>::value;
-    const char* const derived_dump = is_ordered
-                                     ? R"({"age":1,"name":"Erik","metadata":null})"
-                                     : R"({"age":1,"metadata":null,"name":"Erik"})";
-
-    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE with zero members")
-    {
-        persons::empty_intrusive obj{};
-        Json j = obj;
-        CHECK(j.dump() == "{}");
-        CHECK(j.template get<persons::empty_intrusive>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT with zero members")
-    {
-        persons::empty_intrusive_with_default obj{};
-        Json j = obj;
-        CHECK(j.dump() == "{}");
-        CHECK(j.template get<persons::empty_intrusive_with_default>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE with zero members")
-    {
-        const persons::empty_intrusive_only_serialize obj{};
-        Json j = obj;
-        CHECK(j.dump() == "{}");
-    }
-
-    SECTION("NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE with zero members")
-    {
-        persons::empty_non_intrusive obj{};
-        Json j = obj;
-        CHECK(j.dump() == "{}");
-        CHECK(j.template get<persons::empty_non_intrusive>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT with zero members")
-    {
-        persons::empty_non_intrusive_with_default obj{};
-        Json j = obj;
-        CHECK(j.dump() == "{}");
-        CHECK(j.template get<persons::empty_non_intrusive_with_default>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE with zero members")
-    {
-        const persons::empty_non_intrusive_only_serialize obj{};
-        Json j = obj;
-        CHECK(j.dump() == "{}");
-    }
-
-    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE with zero own members")
-    {
-        persons::empty_derived_intrusive obj{"Erik", 1, nullptr};
-        Json j = obj;
-        CHECK(j.dump() == derived_dump);
-        CHECK(j.template get<persons::empty_derived_intrusive>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT with zero own members")
-    {
-        persons::empty_derived_intrusive_with_default obj{"Erik", 1, nullptr};
-        Json j = obj;
-        CHECK(j.dump() == derived_dump);
-        CHECK(j.template get<persons::empty_derived_intrusive_with_default>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE with zero own members")
-    {
-        const persons::empty_derived_intrusive_only_serialize obj{"Erik", 1, nullptr};
-        Json j = obj;
-        CHECK(j.dump() == derived_dump);
-    }
-
-    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE with zero own members")
-    {
-        persons::empty_derived_non_intrusive obj{"Erik", 1, nullptr};
-        Json j = obj;
-        CHECK(j.dump() == derived_dump);
-        CHECK(j.template get<persons::empty_derived_non_intrusive>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT with zero own members")
-    {
-        persons::empty_derived_non_intrusive_with_default obj{"Erik", 1, nullptr};
-        Json j = obj;
-        CHECK(j.dump() == derived_dump);
-        CHECK(j.template get<persons::empty_derived_non_intrusive_with_default>() == obj);
-    }
-
-    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE with zero own members")
-    {
-        const persons::empty_derived_non_intrusive_only_serialize obj{"Erik", 1, nullptr};
-        Json j = obj;
-        CHECK(j.dump() == derived_dump);
-    }
-}
-
-// Regression test for the argument-count dispatch added for issue #4041: the
-// documented maximum of 63 members must keep working, including for the
-// derived-type macros whose Type,BaseType prefix consumes two dispatch slots.
-TEST_CASE_TEMPLATE("Serialization/deserialization of maximum-member-count types via NLOHMANN_DEFINE_TYPE_*", Json, // NOLINT(readability-math-missing-parentheses, bugprone-throwing-static-initialization)
-                   nlohmann::json, nlohmann::ordered_json)
-{
-    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE with 63 members")
-    {
-        persons::max_members obj{};
-        obj.m1 = 1;
-        obj.m63 = 63;
-        Json j = obj;
-        CHECK(j.size() == 63);
-        const auto obj2 = j.template get<persons::max_members>();
-        CHECK(obj2.m1 == 1);
-        CHECK(obj2.m63 == 63);
-    }
-
-    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE with 63 own members")
-    {
-        persons::max_members_derived obj{};
-        obj.base_value = 7;
-        obj.m1 = 1;
-        obj.m63 = 63;
-        Json j = obj;
-        CHECK(j.size() == 64);
-        const auto obj2 = j.template get<persons::max_members_derived>();
-        CHECK(obj2.base_value == 7);
-        CHECK(obj2.m1 == 1);
-        CHECK(obj2.m63 == 63);
-    }
-}

tools/api_checker/POLICY.md

@@ -0,0 +1,127 @@
+# Public API Policy
+
+This document defines what counts as the **public API** of nlohmann/json for the purposes of the
+`tools/api_checker/` tooling, what stability is (and is not) guaranteed, and how API changes are
+classified as breaking or feature additions. It exists so that "public API" is a checkable, mechanical
+property of the source, not a matter of convention or memory — see
+[Discussion #3691](https://github.com/nlohmann/json/discussions/3691) for the original motivation.
+
+## What counts as public API
+
+The public API surface is derived from C++ semantics (class templates, access specifiers, namespace
+scoping) by `extract_api.py`, not from the presence of documentation. It consists of:
+
+1. **Public members of six class templates**: `basic_json`, `adl_serializer`,
+   `byte_container_with_subtype`, `json_pointer`, `json_sax`, `ordered_map`. Specifically, the *primary
+   template definition* (`CLASS_TEMPLATE` cursor with `is_definition() == True`) — never an implicit
+   instantiation, which silently drops SFINAE-guarded overloads. Two tiers apply:
+   - **Callable tier** (methods, constructors, destructors, conversion operators, function templates):
+     every public callable requires its own `@sa` documentation link, without exception.
+   - **Type tier** (public type aliases): requires `@sa`, except for a fixed exemption list of
+     STL-container named-requirement aliases that mirror standard-library conventions rather than being
+     independently documented: `value_type`, `reference`, `const_reference`, `pointer`, `const_pointer`,
+     `iterator`, `const_iterator`, `reverse_iterator`, `const_reverse_iterator`, `difference_type`,
+     `size_type`, `allocator_type`, `key_type`, `mapped_type`. This list is defined once, in
+     `extract_api.py`'s `stl_exempt` set, and referenced here rather than duplicated.
+2. **Free functions and operators in `nlohmann::`**, including `nlohmann::literals::json_literals`
+   (the `operator""_json` / `operator""_json_pointer` user-defined literals). Comparison and stream
+   operators on `basic_json` and `json_pointer`, `operator/`, `swap`.
+3. **The six alias-exposed exception types**: `basic_json::exception`, `parse_error`,
+   `invalid_iterator`, `type_error`, `out_of_range`, `other_error`. These are public `TYPE_ALIAS_DECL`s
+   in `basic_json` (e.g. `using exception = detail::exception;`) whose underlying class is physically
+   defined in `nlohmann::detail::exceptions.hpp`. `extract_api.py` follows the alias to find the `@sa` on
+   the underlying `detail::` class definition, since that's where the existing documentation convention
+   places it. Each exception class is documented as *one page* — its individual members (`what()`, `id`)
+   are not separately tracked, matching the existing one-page-per-class convention.
+4. **Macros**, governed separately by `docs/mkdocs/docs/api/macros/` (the curated list of ~30 pages is
+   authoritative) and cross-checked, advisory-only, by `check_macros.py`. See "Known limitations" below
+   for why macros can't be checked the same way as everything else.
+
+## What's excluded
+
+- **Everything in `nlohmann::detail::`**, with the one narrow exception above (exception-type aliases).
+  **No stability is guaranteed for any symbol in the `detail::` namespace — clients must not rely on it**,
+  regardless of whether a given `detail::` symbol happens to be reachable from user code today. This is
+  an explicit, deliberate policy, not an oversight.
+- **Private and protected members**, even of the six tracked classes. `extract_api.py` walks non-public
+  members only to check they don't carry a stray `@sa` (a documentation leak) — never to add them to the
+  public surface.
+- **The ABI inline-namespace segment** (`json_abi_v3_12_0`, `json_abi_diag_v3_12_0`, etc. — see
+  [docs/mkdocs/docs/features/namespace.md](../../docs/mkdocs/docs/features/namespace.md)). This is a
+  version-tag identity concern for `diff_api.py` (it must not make every release look like the entire API
+  was removed and re-added), not a scoping or visibility concern — the symbols inside it are public or
+  not independent of the tag.
+
+## Breaking vs. feature classification
+
+`diff_api.py` compares the `public_api` surface of two snapshots using an overload-disambiguating
+identity — `(scope, identity_name, kind, signature)`, where `signature` is the declaration's own
+source text (return type, name, parameter list, trailing qualifiers; comments and constructors'
+member-initializer-lists stripped). This is the third identity scheme this tooling has used; the
+first two were each found broken by testing against real release tags, not by inspection — see
+`extract_api.py`'s `identity_key()` docstring for the full history (a naive params-only key silently
+collided on overloads differing only by constness/SFINAE; libclang's USR fixed that but encoded the
+*enclosing class template's own arity*, so a single backward-compatible template-parameter addition
+made ~228 of 330 `basic_json` entries look "changed" between two real releases with zero actual
+breaking changes among them).
+
+- An identity present only in the **new** snapshot → **feature** (addition).
+- An identity present only in the **old** snapshot → **breaking** (removal).
+- The same `(scope, name)` with one identity removed and a different one added → reported as a
+  **changed overload**, classified breaking by default. No automatic overload-compatibility reasoning
+  is attempted — whether a signature change is source-compatible is a judgment call for a human
+  reviewer, not a sound problem for a CI tool to solve unsupervised.
+
+## Stable per-release API history
+
+`tools/api_checker/history/<tag>.json` holds one immutable, committed API-surface record per
+released `v3.*` tag (captured via `snapshot_release.py`; see `tools/api_checker/README.md` and
+`tools/api_checker/history/README.md`). `diff_api.py` reads from here automatically when a ref
+matches a stored file, instead of live-extracting via `git archive` every time.
+
+Every surface file (the live `api_surface.json` and every `history/*.json` record) carries a
+`format_version` integer. **Bump it whenever a change to the schema, or to the identity-computing
+algorithm (`get_signature_text()`/`get_identity_name()`/`identity_key()` in `extract_api.py`), could
+alter the `signature` or `identity_name` text for otherwise-unchanged source.** `diff_api.py` refuses
+by default to compare two surfaces with different `format_version` values — this is a direct,
+mechanical safeguard against the exact class of bug that motivated the current identity scheme (see
+above): a silent algorithm change corrupting every historical comparison with no way to detect it.
+An explicit `--allow-format-mismatch` flag exists for a deliberate, informed comparison anyway.
+
+Practical implication for anyone changing `extract_api.py`'s identity logic: bump
+`SURFACE_FORMAT_VERSION`, and treat every already-committed `history/*.json` file as needing a
+`--force` regeneration (reviewed, not blind) before it can be meaningfully compared against surfaces
+produced by the new algorithm version.
+
+## Stability guarantees
+
+This tooling makes the project's existing commitments *mechanically checkable* — it does not introduce a
+new promise:
+
+- `ChangeLog.md` states the project "adheres to [Semantic Versioning](http://semver.org/)."
+- [docs/mkdocs/docs/home/releases.md](../../docs/mkdocs/docs/home/releases.md) marks every 3.x release "All
+  changes are backward-compatible" (except 3.0.0 itself, a major bump with a migration guide).
+- `tests/abi/` provides a complementary, narrower guarantee: ABI/link compatibility *within one ABI tag*.
+  That is a binary-compatibility concern; this tooling's concern is source/API-level — a symbol can be
+  ABI-stable and still be a source-breaking change (e.g. a removed overload), or vice versa.
+
+## Known limitations
+
+- **Macros have no C++ access-specifier concept**, so the public/private test that works for classes
+  doesn't transfer. Only a minority of documented macro `#define`s have an attached `@sa`-style comment
+  (the `#ifndef X / #define X value #endif` idiom has no natural comment-attachment point), and internal
+  helper macros live in the same files as public configuration macros, so no path-based exclusion works
+  either. `check_macros.py` therefore only checks one direction: that every documented macro still has a
+  matching `#define` somewhere under `include/nlohmann/` (catches stale/renamed doc pages). It does
+  **not** attempt to detect undocumented macros — no reliable signal exists for that direction with the
+  current codebase conventions, and this tool doesn't pretend otherwise.
+- **`diff_api.py` does not track exception specifications or template-parameter-only changes.** A
+  function whose `noexcept` status changes, or whose template parameter list changes without altering
+  its externally-visible identity, will not be flagged.
+- **Known API-hygiene gap, surfaced by this tooling rather than fixed**:
+  `basic_json::insert_iterator` (a `public` member per C++ access rules) is a helper used internally by
+  `insert()`; its own source comment calls it "Helper for insertion of an iterator." It has no
+  documentation page and is deliberately left undocumented rather than either speculatively documented or
+  silently exempted — this is exactly the class of undocumented-and-probably-shouldn't-be-public symbol
+  this tooling exists to surface, per the motivating discussion. A future PR may reclassify it as private
+  as a (breaking, ABI-relevant) cleanup; that is out of scope here.

tools/api_checker/README.md

@@ -0,0 +1,392 @@
+# API Checker Tools
+
+Tooling to extract, validate, and track changes to the public API surface of nlohmann/json.
+
+## Overview
+
+These tools use libclang AST parsing to programmatically derive "the public API" from C++ semantics
+(class templates, access specifiers, namespace scoping) — independently of documentation status. The
+extracted surface is the source of truth for what is considered "public API." On top of this, the tools
+verify that every public entity carries a documentation link and detect API changes between releases.
+A per-release historical record lives in [`history/`](history/README.md), one file per tagged `v3.*`
+release, so past API changes can be derived without re-running libclang against old git refs.
+
+See [POLICY.md](POLICY.md) for the full definition of what counts as public API, what's excluded, how
+breaking vs. feature changes are classified, and known limitations.
+
+## Installation
+
+Install dependencies:
+
+```bash
+pip install -r tools/api_checker/requirements.txt
+```
+
+Requires:
+- Python 3.7+
+- libclang 18.1.1 (installed via pip)
+- clang++ or clang (system package, for include-path discovery only — does not need to
+  version-match the pinned libclang wheel)
+
+## Tools
+
+### extract_api.py
+
+Extract the public API surface by parsing C++ AST using libclang. Produces two different outputs for
+two different consumers — see "Two outputs, one extraction pass" below for why.
+
+**Usage:**
+```bash
+python3 tools/api_checker/extract_api.py \
+  --header include/nlohmann/json.hpp \
+  --include include \
+  --output api_snapshot.json \
+  --surface-output api_surface.json
+```
+
+**Options:**
+- `--header PATH` — Header file to analyze (default: `include/nlohmann/json.hpp`)
+- `--include PATH` — Include directory for parsing (default: `include`)
+- `--output PATH` — Full snapshot output (location + doc status; default: `api_snapshot.json`)
+- `--surface-output PATH` — Minimal surface output (identity only; omit to skip)
+- `--extra-isystem PATH` — Extra `-isystem` include path (repeatable), in case system-include
+  discovery via `clang++ -E -v` ever fails on a given runner image
+- `--self-test` — Run self-tests and exit (validates ABI-tag stripping)
+
+**How it works:**
+Parses the header file using libclang with `PARSE_DETAILED_PROCESSING_RECORD`, discovers system
+includes via `clang++ -E -x c++ -v /dev/null`, and walks the AST:
+
+1. For each of the 6 public class templates (`basic_json`, `adl_serializer`, `byte_container_with_subtype`,
+   `json_pointer`, `json_sax`, `ordered_map`): locate the `CLASS_TEMPLATE` cursor with `is_definition() == True`
+   — never a `CLASS_DECL` implicit instantiation, which silently drops SFINAE-guarded overloads
+2. Extract public members: `CXX_METHOD`, `CONSTRUCTOR`, `DESTRUCTOR`, `CONVERSION_FUNCTION`, `FUNCTION_TEMPLATE`
+   (callable tier — strict `@sa` requirement), and `TYPE_ALIAS_DECL` (type tier — with STL-container exemptions)
+3. Extract free functions in `nlohmann::` namespace (excluding `detail::` and `std::`)
+4. Normalize away ABI inline-namespace (regex `::json_abi[a-z_]*_v\d+_\d+_\d+` → `::`)
+5. Use overload-disambiguating identity keys built from raw source-text signature capture,
+   ABI-tag-stripped — see "Identity keys" below
+
+**Two outputs, one extraction pass:**
+- `--output` (full snapshot): each entry carries `location` (file:line) and documentation status
+  (`doc_url`, `has_sa`). Consumed by `check_docs.py`. **Not meant to be committed** — `location` shifts
+  on any unrelated code edit and `doc_url` changes when doc pages move, so a diff of this file mixes real
+  API changes with pure noise.
+- `--surface-output` (minimal surface): each entry has only `scope`, `kind`, `name`, `identity_name`,
+  `tier`, `signature`, and `pretty_signature` — nothing that can change without the API itself changing.
+  **This is the file that gets committed** (`tools/api_checker/api_surface.json` for the current
+  working tree, `tools/api_checker/history/<tag>.json` per released tag) and diffed by `diff_api.py`.
+
+**Identity keys — three approaches were tried and rejected before arriving at the current one:**
+1. `{scope, name, kind, params}` from `cursor.get_arguments()`: silently collided for any overload set
+   differentiated only by constness, ref-qualifiers, or SFINAE constraints rather than parameter types —
+   confirmed empirically: `basic_json`'s two zero-argument `get()` overloads (one `const`, one not) both
+   produced `params=[]` and silently overwrote each other. A full scan found **59 such silent overwrites
+   across 27 colliding names**.
+2. libclang's USR: correctly disambiguates every overload (it encodes the full mangled signature) — but
+   *also* encodes the enclosing class template's own arity into every member's USR. Confirmed
+   empirically against real release tags: `basic_json` gaining one new defaulted template parameter
+   between v3.11.2 and v3.11.3 (a backward-compatible change) changed literally every member's USR,
+   which made `diff_api.py` report **228 of 330 entries as "changed"** for a release with zero real
+   breaking changes among them.
+3. **Current approach**: raw source-text signature capture — `identity = (scope, identity_name, kind,
+   signature)`, where `signature` is the declaration's own text (return type, name, parameter list,
+   trailing cv/ref/noexcept qualifiers; comments and constructors' member-initializer-lists stripped;
+   stops before the function body) read directly via the cursor's byte-offset extent. This is what's
+   actually written in source — declared names like `ValueType`, never a resolved
+   `basic_json<T0,...,T10>` — so it's immune to the class-arity problem above. Verified by manually
+   cross-referencing every "added"/"removed"/"changed" entry in three real release-to-release diffs
+   (v3.11.2→v3.11.3, v3.11.3→v3.12.0, v3.12.0→HEAD) against the actual `git diff` of the source — every
+   one confirmed genuine. Full details, including several further edge-case fixes found the same way
+   (a libclang tokenizer gap, comment-stripping, constructor-name arity-poisoning), are in
+   `extract_api.py`'s `identity_key()`/`get_signature_text()` docstrings.
+
+**Output (full snapshot, from `--output`):**
+```json
+{
+  "meta": {
+    "extracted_from": "include/nlohmann/json.hpp"
+  },
+  "public_api": {
+    "<opaque internal key, not meant to be read>": {
+      "scope": "nlohmann::basic_json",
+      "name": "parse",
+      "identity_name": "parse",
+      "kind": "CXX_METHOD",
+      "tier": "callable",
+      "signature": "static basic_json parse ( InputType && i , ... )",
+      "location": "include/nlohmann/json.hpp:4104",
+      "doc_url": "https://json.nlohmann.me/api/basic_json/parse/",
+      "has_sa": true,
+      "pretty_signature": "nlohmann::basic_json::parse"
+    }
+  },
+  "documented_non_public": []
+}
+```
+
+`documented_non_public` lists entities **not** part of the public surface (private/protected members of
+the six tracked classes) that surprisingly carry a real `@sa` URL — a genuine documentation leak. It does
+not list public entries that merely lack `@sa`; that's `check_docs.py`'s job.
+
+**Output (surface, from `--surface-output`):**
+```json
+{
+  "format_version": 1,
+  "meta": {
+    "extracted_from": "include/nlohmann/json.hpp"
+  },
+  "public_api": [
+    {
+      "scope": "nlohmann::basic_json",
+      "kind": "CXX_METHOD",
+      "name": "parse",
+      "identity_name": "parse",
+      "tier": "callable",
+      "signature": "static basic_json parse ( InputType && i , parser_callback_t cb = nullptr , const bool allow_exceptions = true , const bool ignore_comments = false )",
+      "pretty_signature": "nlohmann::basic_json::parse"
+    }
+  ]
+}
+```
+
+A flat, sorted list of self-describing records — `signature`/`identity_name` are the same values
+`identity_key()` joins into one opaque internal string, exposed here as explicit fields so the file is
+readable and diffable by inspection, not just by tooling. `identity_name` differs from `name` only for
+constructors/destructors (a canonical `"(constructor)"`/`"(destructor)"` placeholder — see
+`get_identity_name()`'s docstring for why `cursor.spelling` isn't used directly there).
+
+`format_version` guards against a future change to this schema or to the identity-computing algorithm
+silently corrupting a comparison against an older stored surface — bump it whenever such a change could
+alter `signature`/`identity_name` text for otherwise-unchanged source (see `diff_api.py`).
+
+### check_docs.py
+
+Verify that all public API entries have valid documentation links and that no non-public entities
+carry `@sa` comments.
+
+**Usage:**
+```bash
+python3 tools/api_checker/check_docs.py --snapshot api_snapshot.json
+```
+
+**Options:**
+- `--snapshot PATH` — Full API snapshot JSON file from `extract_api.py --output` (default: `api_snapshot.json`)
+
+**How it works:**
+Two-pass validation over the extracted snapshot:
+
+1. For every `public_api` entry (callable tier, and type tier minus STL exemptions): flag if missing `@sa`,
+   flag if `@sa` URL doesn't resolve to an existing documentation file (following `docs/mkdocs/mkdocs.yml`'s
+   `redirect_maps` when a page has moved, and trying the class-overview conventions used by different
+   classes — flat `<class>.md`, nested `<class>/<class>.md`, nested `<class>/index.md`)
+2. For every `documented_non_public` entry: flag as unexpected `@sa` on a non-public entity
+
+**Output:**
+Prints warnings for each issue, categorized by rule:
+- `docs/missing_sa_comment` — public API without `@sa` documentation link
+- `docs/missing_doc_file` — `@sa` URL points to non-existent `.md` file
+- `docs/invalid_sa_url` — malformed `@sa` URL
+- `docs/sa_on_non_public` — unexpected `@sa` on a non-public entity
+
+Exits with status 0 if all checks pass, 1 if issues found.
+
+### diff_api.py
+
+Compare the public API surface between two refs and classify changes as feature (added) or
+breaking (removed / changed overload).
+
+**Usage:**
+```bash
+python3 tools/api_checker/diff_api.py --old v3.12.0 --new HEAD
+python3 tools/api_checker/diff_api.py --old v3.11.2 --new v3.11.3          # both resolved from history/
+python3 tools/api_checker/diff_api.py --old v3.12.0 --new HEAD --fail-on-breaking
+python3 tools/api_checker/diff_api.py --old-file a.json --new-file b.json  # compare two files directly
+```
+
+**Options:**
+- `--old REF` / `--new REF` — Refs to compare (tags, branches, commits). `--new` defaults to `HEAD`.
+  Each is resolved by checking `tools/api_checker/history/<ref>.json` first (fast — no libclang or
+  git-archive needed), falling back to live extraction if no matching file exists there.
+- `--old-file PATH` / `--new-file PATH` — Load an arbitrary surface JSON file directly, bypassing
+  both git and `tools/api_checker/history/`. Mutually exclusive with `--old`/`--new` respectively.
+- `--no-history` — Force live extraction even when a matching `tools/api_checker/history/<ref>.json`
+  exists. Useful to check that a stored record is still faithful to a fresh run of the current tool.
+- `--allow-format-mismatch` — Proceed even if the two surfaces have different `format_version`
+  (otherwise `diff_api.py` refuses — see below).
+- `--header PATH` / `--include PATH` — For live extraction only (default:
+  `include/nlohmann/json.hpp` / `include`)
+- `--fail-on-breaking` — Exit with status 1 if breaking changes are detected
+
+**How it works:**
+For a ref not found in `tools/api_checker/history/`, checks out the **full `include/` tree** at
+that ref into a temp directory via `git archive` (a single-file checkout of `json.hpp` is not
+enough — it `#include`s dozens of other headers that must exist at the same ref), then runs the
+*current* `extract_api.py --surface-output` against it. Diffs the two surfaces by identity
+(`scope`, `identity_name`, `kind`, `signature`):
+- Identity only in the new surface → **feature**.
+- Identity only in the old surface → **breaking** (removed).
+- Same `(scope, name)` with a removed identity and an added identity → grouped as a **changed
+  overload**, breaking by default. No automatic overload-compatibility reasoning is attempted — a
+  human judges whether the change is actually source-compatible.
+
+Before diffing, the two surfaces' `format_version` fields are compared; a mismatch aborts with an
+error (override with `--allow-format-mismatch`) rather than silently producing an unsound diff — see
+`extract_api.py`'s `SURFACE_FORMAT_VERSION` docstring for the incident that motivated this guard.
+
+ABI-tag stripping is inherited automatically since both extractions go through the same
+`extract_api.py`.
+
+**Use case:** Run before cutting a release to verify the changelog correctly categorizes changes as
+breaking vs. features.
+
+### snapshot_release.py
+
+Capture an immutable, per-release API surface record into `tools/api_checker/history/<tag>.json`.
+This is what makes `diff_api.py` fast for released tags — see "How it works" above.
+
+**Usage:**
+```bash
+python3 tools/api_checker/snapshot_release.py --ref v3.12.0
+python3 tools/api_checker/snapshot_release.py --ref v3.11.0 --ref v3.12.0   # repeatable
+python3 tools/api_checker/snapshot_release.py --all-tags                    # every v3.* tag
+python3 tools/api_checker/snapshot_release.py --ref v3.12.0 --force         # overwrite an existing record
+```
+
+**Options:**
+- `--ref REF` — Git tag to snapshot; repeatable
+- `--all-tags` — Snapshot every `v3.*` tag (existing files are skipped unless `--force`)
+- `--output-dir PATH` — Where to write (default: `tools/api_checker/history/`)
+- `--force` — Overwrite an existing history file. History files are immutable by convention —
+  only pass this for a deliberate, reviewed regeneration; review the resulting diff before
+  committing
+- `--header PATH` / `--include PATH` — Same as `diff_api.py`'s live-extraction options
+
+**How it works:** Reuses `diff_api.py`'s `extract_surface_for_ref()` for the git-archive-and-extract
+work, then adds `generated_at`/`generator` provenance and writes the result to
+`tools/api_checker/history/<ref>.json`. Given multiple refs (or `--all-tags`), does **not** abort
+the batch on one failing ref — collects failures and prints a summary at the end, so one
+unparseable old tag doesn't block backfilling the releases that do work. See
+`tools/api_checker/history/README.md` for the currently-known gaps (pre-restructuring tags that
+predate the `include/nlohmann/` layout entirely).
+
+**Not CI-automated** — this is a manual step in the release checklist (see below), by design.
+
+### check_macros.py
+
+Advisory-only cross-check between documented macros and their `#define`/reference sites. **Never blocks
+CI**, regardless of findings.
+
+**Usage:**
+```bash
+python3 tools/api_checker/check_macros.py
+```
+
+**Options:**
+- `--macros-dir PATH` — Directory of macro doc pages (default: `docs/mkdocs/docs/api/macros`)
+- `--include-dir PATH` — Directory to search for `#define`/reference sites (default: `include/nlohmann`)
+
+**How it works:**
+For each `.md` page under `docs/mkdocs/docs/api/macros/` (excluding `index.md`), extracts the macro
+name(s) from the H1 heading — handling both plain single-macro headings and multi-line HTML headings
+that list a family of related macros (e.g. the `NLOHMANN_DEFINE_DERIVED_TYPE_*` family) — then checks
+whether each name is defined **or referenced** (`#define`, `#ifdef`, `#ifndef`, `defined(...)`) anywhere
+under `include/nlohmann/`. Referenced-but-not-defined is deliberately accepted: macros like
+`JSON_NOEXCEPTION` or `JSON_THROW_USER` are user-supplied overrides that the library only checks for,
+never defines itself.
+
+Only checks the documented-macro-still-exists direction (catches stale/renamed doc pages). Does **not**
+check the converse (undocumented macros) — see [POLICY.md](POLICY.md)'s "Known limitations" for why.
+
+## Continuous Integration
+
+A GitHub Actions workflow (`.github/workflows/check_api_docs.yml`) runs on every pull request:
+
+1. Installs `clang` (system package, for include discovery) and Python dependencies
+2. Runs `extract_api.py`, regenerating both the ephemeral full snapshot and the tracked
+   `tools/api_checker/api_surface.json`
+3. Runs `check_docs.py` — **Phase 1: advisory** (`continue-on-error: true`), surfacing the doc backlog
+   without failing the job while it's burned down. Will flip to blocking once the backlog is cleared.
+4. Runs `check_macros.py` — always advisory
+5. Diffs `tools/api_checker/api_surface.json` against the regenerated copy — **blocking from the start**
+   (unlike the doc-backlog check, this is purely mechanical regeneration with no backlog to phase in,
+   matching the precedent set by `check_amalgamation.yml`). Uploads a patch artifact if it differs, so
+   contributors can `git apply` it instead of installing libclang locally.
+
+## Workflow: Adding New Public API
+
+1. Add the new public method/function to the header
+2. Add a `/// @sa https://json.nlohmann.me/api/<class>/<member>/` comment above it
+3. Create the corresponding documentation page at `docs/mkdocs/docs/api/<class>/<member>.md` and a
+   `mkdocs.yml` nav entry
+4. Regenerate and commit the tracked surface file:
+   ```bash
+   python3 tools/api_checker/extract_api.py --surface-output tools/api_checker/api_surface.json
+   git add tools/api_checker/api_surface.json
+   ```
+5. Push your PR — CI verifies both the doc link and that the surface file is up to date
+
+## Workflow: Release Checklist
+
+Before cutting a release:
+
+```bash
+# Diff current API against the previous release
+python3 tools/api_checker/diff_api.py --old v3.12.0 --new HEAD
+
+# Review the output to verify the changelog correctly categorizes breaking vs. feature changes
+```
+
+After tagging the release:
+
+```bash
+# Capture and commit the new tag's API surface, so future diffs against it hit the fast,
+# stored-file path instead of live-extracting every time. A manual step, not CI-automated.
+python3 tools/api_checker/snapshot_release.py --ref v3.13.0
+git add tools/api_checker/history/v3.13.0.json
+```
+
+## Troubleshooting
+
+**libclang not found:**
+```
+Error: Could not locate libclang library
+```
+→ Ensure libclang is installed: `python3 -m pip install libclang==18.1.1`
+
+**Parse errors in header:**
+```
+Parse errors encountered:
+  ... list of diagnostics ...
+```
+→ Check that system includes can be discovered. Run `clang++ -E -x c++ -v /dev/null` and verify
+the output includes a section titled `#include <...> search starts here:` with system paths.
+If include discovery fails, use `--extra-isystem PATH` to provide additional paths.
+
+**No API entries extracted (or very few):**
+- Check that the header file exists and is valid C++: `ls -la include/nlohmann/json.hpp`
+- Verify that no parse errors occur above
+- Confirm that you're targeting a `CLASS_TEMPLATE` definition, not an implicit instantiation
+  (the tool logs `Found N public API entries` — a zero or very small count suggests the wrong cursor kind)
+
+**Doc link returns 404:**
+- Verify the file exists at the expected path: `docs/mkdocs/docs/api/<class>/<member>.md`
+- Check for URL encoding issues (e.g., `operator[]` → `operator%5B%5D`)
+- Verify the URL structure in the `@sa` comment: should be `https://json.nlohmann.me/api/<path>/`
+- Check `docs/mkdocs/mkdocs.yml`'s `redirect_maps` if the page has moved
+
+**`tools/api_checker/api_surface.json` is out of date in CI:**
+→ Regenerate and commit it: `python3 tools/api_checker/extract_api.py --surface-output tools/api_checker/api_surface.json`
+
+**`diff_api.py` refuses with "format_version mismatch":**
+→ One side is a stored surface (live `api_surface.json` or a `tools/api_checker/history/*.json`
+file) captured with an older/newer version of `extract_api.py`'s identity-computing algorithm than
+the other side. Comparing them directly could produce an unsound diff (this is exactly the failure
+mode that motivated adding the check — see `extract_api.py`'s `SURFACE_FORMAT_VERSION` docstring).
+Either regenerate the older side with the current tool, or pass `--allow-format-mismatch` if you
+understand the risk and want to proceed anyway.
+
+## Contributing
+
+Report bugs or suggest improvements to [Discussion #3691](https://github.com/nlohmann/json/discussions/3691).
+Read [POLICY.md](POLICY.md) first for the definition of public API this tooling enforces.

tools/api_checker/check_docs.py

@@ -0,0 +1,182 @@
+#!/usr/bin/env python3
+"""Verify that public API entries have documentation links.
+
+Consumes an API snapshot from extract_api.py and checks:
+1. Every public callable/type-tier entry has an @sa comment (with exceptions)
+2. Every @sa URL resolves to an existing documentation file
+3. No @sa comments appear on non-public entities
+"""
+
+import argparse
+import json
+import os
+import re
+import subprocess
+import sys
+from urllib.parse import unquote
+
+warnings = 0
+
+# STL-container-named-requirement aliases that are exempt from @sa requirement
+STL_EXEMPT = {'value_type', 'reference', 'const_reference', 'pointer', 'const_pointer',
+              'iterator', 'const_iterator', 'reverse_iterator', 'const_reverse_iterator',
+              'difference_type', 'size_type', 'allocator_type', 'key_type', 'mapped_type'}
+
+
+def get_repo_root():
+    """Find the repository root via git, so this script works regardless of invoking CWD."""
+    try:
+        result = subprocess.run(
+            ['git', 'rev-parse', '--show-toplevel'],
+            capture_output=True, text=True, check=True, timeout=10
+        )
+        return result.stdout.strip()
+    except (subprocess.CalledProcessError, FileNotFoundError, subprocess.TimeoutExpired):
+        return os.getcwd()
+
+
+REPO_ROOT = get_repo_root()
+MKDOCS_YML = os.path.join(REPO_ROOT, 'docs', 'mkdocs', 'mkdocs.yml')
+
+
+def load_redirect_map() -> dict:
+    """Parse the redirect_maps block of docs/mkdocs/mkdocs.yml: {old_relative_path: new_relative_path}.
+
+    mkdocs' redirect plugin lets a doc page move without breaking existing @sa URLs -- e.g.
+    'api/basic_json/operator_ltlt.md' redirects to the real file at 'api/operator_ltlt.md'.
+    Without consulting this map, url_to_docfile() would flag every redirected URL as a broken link.
+    """
+    if not os.path.exists(MKDOCS_YML):
+        return {}
+    with open(MKDOCS_YML) as f:
+        content = f.read()
+    redirect_map = {}
+    for m in re.finditer(r"^\s*'([^']+\.md)':\s*(\S+\.md)\s*$", content, re.MULTILINE):
+        redirect_map[m.group(1)] = m.group(2)
+    return redirect_map
+
+
+REDIRECT_MAP = load_redirect_map()
+
+
+def report(rule: str, location: str, description: str):
+    """Report a documentation issue."""
+    global warnings
+    warnings += 1
+    print(f'{warnings:3}. {location}:  {description} [{rule}]')
+
+
+def url_to_docfile(url: str) -> str | None:
+    """Convert @sa URL to the documentation file it resolves to, following mkdocs redirects."""
+    if not url:
+        return None
+
+    # Extract path after /api/
+    match = re.search(r'/api/(.+?)/?$', url)
+    if not match:
+        return None
+
+    # URL-decode each path component
+    path_parts = [unquote(part) for part in match.group(1).split('/')]
+    relative_path = 'api/' + '/'.join(path_parts) + '.md'
+
+    docs_root = os.path.join(REPO_ROOT, 'docs', 'mkdocs', 'docs')
+    direct_path = os.path.join(docs_root, relative_path)
+
+    # Class-overview URLs (a single path segment after /api/, e.g. ".../api/json_pointer/")
+    # use inconsistent on-disk conventions across classes: ordered_map.md is a flat file,
+    # byte_container_with_subtype/byte_container_with_subtype.md nests under a same-named
+    # file, json_pointer/index.md nests under index.md. Try all observed conventions.
+    candidates = [direct_path]
+    if len(path_parts) == 1:
+        stem = path_parts[0]
+        candidates.append(os.path.join(docs_root, 'api', stem, 'index.md'))
+        candidates.append(os.path.join(docs_root, 'api', stem, stem + '.md'))
+
+    redirected = REDIRECT_MAP.get(relative_path)
+    if redirected:
+        candidates.append(os.path.join(docs_root, redirected))
+
+    for candidate in candidates:
+        if os.path.exists(candidate):
+            return candidate
+
+    # Nothing resolved -- return the direct path so the caller reports a meaningful "missing" location.
+    return direct_path
+
+
+def check_docs(snapshot_path: str):
+    """Check documentation for all API entries."""
+    if not os.path.exists(snapshot_path):
+        print(f"Error: Snapshot file not found: {snapshot_path}")
+        sys.exit(1)
+
+    with open(snapshot_path, 'r') as f:
+        data = json.load(f)
+
+    api = data.get('public_api', {})
+    documented_non_public = data.get('documented_non_public', [])
+
+    print(f"Checking documentation for {len(api)} API entries...")
+    print(120 * "-")
+
+    # Check public API entries
+    for _identity_key, entry in sorted(api.items()):
+        location = entry.get('location', 'unknown')
+        name = entry.get('name', '?')
+        tier = entry.get('tier', '?')
+        doc_url = entry.get('doc_url')
+        has_sa = entry.get('has_sa', False)
+
+        # Skip type_exempt tier entries
+        if tier == 'type_exempt':
+            continue
+
+        # Check for missing @sa
+        if not has_sa:
+            report('docs/missing_sa_comment', location,
+                  f'public API "{name}" (tier: {tier}) has no @sa documentation link')
+            continue
+
+        # Verify URL resolves to an existing file
+        doc_file = url_to_docfile(doc_url)
+        if not doc_file:
+            report('docs/invalid_sa_url', location,
+                  f'public API "{name}" has invalid @sa URL: {doc_url}')
+            continue
+
+        if not os.path.exists(doc_file):
+            display_path = os.path.relpath(doc_file, REPO_ROOT)
+            report('docs/missing_doc_file', location,
+                  f'public API "{name}" @sa URL points to non-existent file: {display_path}')
+
+    # Check documented_non_public entries
+    for entry in documented_non_public:
+        location = entry.get('location', 'unknown')
+        reason = entry.get('reason', '?')
+        report('docs/sa_on_non_public', location,
+              f'@sa comment found on non-public entity: {reason}')
+
+    print(120 * "-")
+
+    if warnings > 0:
+        print(f"\nFound {warnings} documentation issues")
+        return False
+    else:
+        print("\nAll public API entries are properly documented ✓")
+        return True
+
+
+def main():
+    parser = argparse.ArgumentParser(description='Check documentation for public API')
+    parser.add_argument('--snapshot', default='api_snapshot.json',
+                       help='Path to API snapshot JSON file')
+
+    args = parser.parse_args()
+
+    if not check_docs(args.snapshot):
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    main()

tools/api_checker/check_macros.py

@@ -0,0 +1,131 @@
+#!/usr/bin/env python3
+"""Advisory-only cross-check between documented macros and their #define sites.
+
+Macros have no C++ access-specifier concept, so the AST-based public/private test that
+extract_api.py uses for classes doesn't transfer -- see tools/api_checker/POLICY.md's "Known
+limitations" section. This script only checks one direction: that every macro documented under
+docs/mkdocs/docs/api/macros/ still has a matching #define somewhere under include/nlohmann/,
+catching stale or renamed doc pages. It does NOT check the converse (undocumented macros) --
+no reliable signal exists for that direction given this codebase's conventions.
+
+Never blocks CI -- always exits 0, even when it reports findings.
+"""
+
+import argparse
+import glob
+import os
+import re
+import sys
+
+MACRO_TOKEN_RE = re.compile(r'\b([A-Z][A-Z0-9_]*)\b')
+
+warnings = 0
+
+
+def report(location: str, description: str):
+    global warnings
+    warnings += 1
+    print(f'{warnings:3}. {location}:  {description}')
+
+
+def extract_macro_names(md_path: str) -> list:
+    """Extract macro name(s) from a doc page's H1 heading.
+
+    Most pages use a single-line markdown heading ('# JSON_ASSERT'). A few document a family of
+    related macros under one page using a multi-line HTML heading listing comma-separated names
+    (e.g. NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, ..._WITH_DEFAULT, ..._ONLY_SERIALIZE). Handle
+    both: collect the heading text (markdown '# ...' line, or everything between <h1> and </h1>,
+    which may span multiple lines), then split on commas.
+    """
+    with open(md_path) as f:
+        content = f.read()
+
+    heading_text = None
+    html_match = re.search(r'<h1>(.*?)</h1>', content, re.DOTALL)
+    if html_match:
+        heading_text = html_match.group(1)
+    else:
+        for line in content.splitlines():
+            if line.startswith('# '):
+                heading_text = line[2:]
+                break
+
+    if not heading_text:
+        return []
+
+    names = []
+    for part in heading_text.split(','):
+        match = MACRO_TOKEN_RE.search(part)
+        if match:
+            names.append(match.group(1))
+    return names
+
+
+def macro_is_referenced(macro_name: str, include_dir: str) -> bool:
+    """Check whether macro_name is defined OR referenced (#ifdef/#ifndef/defined()) anywhere
+    under include_dir.
+
+    Some documented macros (e.g. JSON_NOEXCEPTION, JSON_THROW_USER) are user-supplied overrides:
+    the library only checks whether they're defined, it never #defines them itself. Requiring a
+    literal #define would make this advisory check permanently noisy for that whole category, so
+    presence of any reference is treated as "this macro still exists in the codebase."
+    """
+    pattern = re.compile(
+        r'#\s*define\s+' + re.escape(macro_name) + r'\b'
+        r'|#\s*ifn?def\s+' + re.escape(macro_name) + r'\b'
+        r'|defined\s*\(\s*' + re.escape(macro_name) + r'\s*\)'
+        r'|defined\s+' + re.escape(macro_name) + r'\b'
+    )
+    for root, _dirs, files in os.walk(include_dir):
+        for fname in files:
+            if not fname.endswith('.hpp'):
+                continue
+            path = os.path.join(root, fname)
+            with open(path, encoding='utf-8', errors='ignore') as f:
+                if pattern.search(f.read()):
+                    return True
+    return False
+
+
+def check_macros(macros_dir: str, include_dir: str) -> bool:
+    md_files = sorted(glob.glob(os.path.join(macros_dir, '*.md')))
+    md_files = [f for f in md_files if os.path.basename(f) != 'index.md']
+
+    print(f"Checking {len(md_files)} documented macros against #define sites in {include_dir}...")
+    print(120 * "-")
+
+    for md_path in md_files:
+        macro_names = extract_macro_names(md_path)
+        if not macro_names:
+            report(md_path, "could not extract macro name(s) from H1 heading")
+            continue
+
+        for macro_name in macro_names:
+            if not macro_is_referenced(macro_name, include_dir):
+                report(md_path, f'documented macro "{macro_name}" is not defined or referenced under {include_dir}')
+
+    print(120 * "-")
+
+    if warnings > 0:
+        print(f"\nFound {warnings} stale/renamed macro doc pages (advisory only, not blocking)")
+    else:
+        print("\nAll documented macros have a matching #define ✓")
+
+    return warnings == 0
+
+
+def main():
+    parser = argparse.ArgumentParser(description='Advisory cross-check of documented macros vs. #define sites')
+    parser.add_argument('--macros-dir', default='docs/mkdocs/docs/api/macros',
+                       help='Directory containing macro documentation pages')
+    parser.add_argument('--include-dir', default='include/nlohmann',
+                       help='Directory to search for #define sites')
+
+    args = parser.parse_args()
+    check_macros(args.macros_dir, args.include_dir)
+    # Advisory only -- never fail CI regardless of findings.
+    sys.exit(0)
+
+
+if __name__ == '__main__':
+    main()

tools/api_checker/diff_api.py

@@ -0,0 +1,295 @@
+#!/usr/bin/env python3
+"""Diff the public API surface between two refs to flag breaking vs. feature changes.
+
+A "ref" for --old/--new is resolved in this order:
+1. A stored, committed historical record at tools/api_checker/history/<ref>.json, if one exists
+   and --no-history wasn't passed (fast path -- no libclang/git-archive needed).
+2. Live extraction: check the ref out via `git archive` into a temp dir and run extract_api.py
+   against it (needed for HEAD, branches, or any tag not yet backfilled into history/).
+--old-file/--new-file bypass both and load an arbitrary surface JSON file directly.
+
+Uses extract_api.py's --surface-output (identity-only: scope, kind, name, identity_name, tier,
+signature, pretty_signature -- no location, no doc_url) for both sides, so the diff reflects only
+genuine API changes, never unrelated code motion or documentation-site restructuring. Identity is
+(scope, identity_name, kind, signature) -- see extract_api.py's identity_key()/get_signature_text()
+docstrings for the full history of why this is what it is: a naive {scope,name,kind,params} key
+silently collided on overloads differing only by constness/SFINAE; switching to libclang's USR
+fixed that but encoded the *enclosing class template's own arity* into every member's identity, so
+a single backward-compatible template-parameter addition (confirmed via real release tags
+v3.11.2->v3.11.3) made ~228 of 330 entries look "changed" for a release with no real breaking
+changes. The current raw-source-text-signature approach was arrived at, and each of several further
+refinements verified, by testing against real historical releases -- not by inspecting code alone.
+"""
+
+import argparse
+import json
+import os
+import subprocess
+import sys
+import tempfile
+from collections import defaultdict
+
+SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+HISTORY_DIR = os.path.join(SCRIPT_DIR, 'history')
+
+# The format_version this build of diff_api.py understands. Kept in sync with
+# extract_api.py's SURFACE_FORMAT_VERSION by convention (both bump together whenever the
+# identity-computing algorithm changes) -- imported directly so there's exactly one source of
+# truth, not two constants that can drift apart.
+sys.path.insert(0, SCRIPT_DIR)
+from extract_api import SURFACE_FORMAT_VERSION  # noqa: E402
+
+
+def resolve_commit_sha(ref: str) -> str | None:
+    """Resolve a ref to its full commit sha, or None if that fails."""
+    try:
+        result = subprocess.run(
+            ['git', 'rev-parse', ref],
+            capture_output=True, text=True, check=True, timeout=10
+        )
+        return result.stdout.strip()
+    except (subprocess.CalledProcessError, FileNotFoundError, subprocess.TimeoutExpired):
+        return None
+
+
+def extract_surface_for_ref(ref: str, header: str = 'include/nlohmann/json.hpp',
+                            include: str = 'include') -> dict:
+    """Check out the full include/ tree at `ref` into a temp dir and extract its API surface.
+
+    A single-file checkout of json.hpp is not enough: json.hpp #includes dozens of other
+    headers under nlohmann/detail/ that must exist at the same ref for parsing to succeed.
+
+    Returns the full loaded surface JSON (format_version, meta, public_api list), with `ref` and
+    the resolved commit sha recorded in meta -- callers that only care about the diff can ignore
+    these; snapshot_release.py uses them as a historical record's provenance.
+    """
+    with tempfile.TemporaryDirectory(prefix='api_checker_') as tmpdir:
+        archive = subprocess.run(
+            ['git', 'archive', ref, '--', 'include'],
+            capture_output=True, check=True
+        )
+        subprocess.run(['tar', '-x', '-C', tmpdir], input=archive.stdout, check=True)
+
+        ref_include = os.path.join(tmpdir, include)
+        ref_header = os.path.join(tmpdir, header)
+        if not os.path.exists(ref_header):
+            print(f"Error: {header} does not exist at ref {ref}")
+            sys.exit(1)
+
+        surface_output = os.path.join(tmpdir, 'surface.json')
+        result = subprocess.run(
+            [sys.executable, os.path.join(SCRIPT_DIR, 'extract_api.py'),
+             '--header', ref_header,
+             '--include', ref_include,
+             '--output', os.path.join(tmpdir, 'snapshot.json'),
+             '--surface-output', surface_output],
+            capture_output=True, text=True
+        )
+        if result.returncode != 0:
+            print(f"Error extracting API at ref {ref}:")
+            print(result.stdout)
+            print(result.stderr)
+            sys.exit(1)
+
+        with open(surface_output) as f:
+            surface = json.load(f)
+
+    # extract_api.py resolved 'extracted_from' relative to *its own* invocation cwd/repo-root
+    # detection, which inside this temp checkout is meaningless (a path like
+    # "../../../../var/folders/.../tmp.XXXX/include/nlohmann/json.hpp") -- overwrite with the
+    # stable, repo-relative header path actually passed in, so a stored history file's metadata
+    # doesn't embed a throwaway temp directory name.
+    surface.setdefault('meta', {})['extracted_from'] = header
+    surface['meta']['ref'] = ref
+    commit_sha = resolve_commit_sha(ref)
+    if commit_sha:
+        surface['meta']['commit'] = commit_sha
+    return surface
+
+
+def load_surface_file(path: str) -> dict:
+    """Load a surface JSON file from disk (a stored history/ record or an explicit --old-file/--new-file)."""
+    with open(path) as f:
+        return json.load(f)
+
+
+def resolve_surface(ref: str | None, explicit_file: str | None, header: str, include: str,
+                    no_history: bool) -> tuple:
+    """Resolve one side of a diff. Returns (surface_dict, description_string_for_display)."""
+    if explicit_file:
+        return load_surface_file(explicit_file), f"file:{explicit_file}"
+
+    history_path = os.path.join(HISTORY_DIR, f"{ref}.json")
+    if not no_history and os.path.exists(history_path):
+        return load_surface_file(history_path), f"history:{ref}"
+
+    return extract_surface_for_ref(ref, header, include), f"live:{ref}"
+
+
+def build_identity_dict(public_api: list) -> dict:
+    """Group a surface's public_api list by identity for diffing.
+
+    Identity is (scope, identity_name, kind, signature) -- the same four components
+    extract_api.py's identity_key() joins into one opaque string internally, exposed here as
+    explicit fields on each record (see extract_api.py's write_surface()) so this reconstruction
+    is a plain, visible tuple lookup rather than decoding anything.
+    """
+    return {
+        (entry['scope'], entry['identity_name'], entry['kind'], entry['signature']): entry
+        for entry in public_api
+    }
+
+
+def diff_surfaces(old_api: dict, new_api: dict) -> dict:
+    """Compare two API surfaces by identity key, grouping same-(scope,name) changes."""
+    old_keys = set(old_api.keys())
+    new_keys = set(new_api.keys())
+
+    added_keys = new_keys - old_keys
+    removed_keys = old_keys - new_keys
+
+    # Group removed/added entries by (scope, name) to detect "changed overload" pairs,
+    # rather than reporting a same-named removal+addition as two unrelated changes.
+    removed_by_name = defaultdict(list)
+    for key in removed_keys:
+        entry = old_api[key]
+        removed_by_name[(entry['scope'], entry['name'])].append(key)
+
+    added_by_name = defaultdict(list)
+    for key in added_keys:
+        entry = new_api[key]
+        added_by_name[(entry['scope'], entry['name'])].append(key)
+
+    changed = []
+    pure_added = []
+    pure_removed = []
+
+    for name, removed_list in removed_by_name.items():
+        if name in added_by_name:
+            added_list = added_by_name.pop(name)
+            for key in removed_list:
+                changed.append({'scope': name[0], 'name': name[1],
+                               'old': old_api[key]['pretty_signature'],
+                               'new': new_api[added_list[0]]['pretty_signature']})
+        else:
+            for key in removed_list:
+                pure_removed.append(old_api[key])
+
+    for name, added_list in added_by_name.items():
+        for key in added_list:
+            pure_added.append(new_api[key])
+
+    return {
+        'added': sorted(pure_added, key=lambda e: e['pretty_signature']),
+        'removed': sorted(pure_removed, key=lambda e: e['pretty_signature']),
+        'changed': sorted(changed, key=lambda e: (e['scope'], e['name'])),
+    }
+
+
+def print_diff(diff: dict, old_desc: str, new_desc: str) -> bool:
+    """Print a human-readable diff report. Returns True if breaking changes were found."""
+    print(120 * "-")
+    print(f"API Diff: {old_desc} -> {new_desc}")
+    print(120 * "-")
+
+    if diff['added']:
+        print(f"\nAdded ({len(diff['added'])} entries) -- feature:")
+        for entry in diff['added']:
+            print(f"  + {entry['pretty_signature']}")
+
+    if diff['removed']:
+        print(f"\nRemoved ({len(diff['removed'])} entries) -- BREAKING:")
+        for entry in diff['removed']:
+            print(f"  - {entry['pretty_signature']}")
+
+    if diff['changed']:
+        print(f"\nChanged overloads ({len(diff['changed'])} entries) -- BREAKING by default:")
+        for entry in diff['changed']:
+            print(f"  ~ {entry['old']}  ->  {entry['new']}")
+
+    if not any([diff['added'], diff['removed'], diff['changed']]):
+        print("\nNo API changes detected")
+
+    print(120 * "-")
+
+    breaking = bool(diff['removed'] or diff['changed'])
+    if breaking:
+        print("\nWARNING: Potential BREAKING CHANGES detected:")
+        print(f"  - {len(diff['removed'])} removed entries")
+        print(f"  - {len(diff['changed'])} changed overloads")
+    if diff['added']:
+        print(f"\nNew features: {len(diff['added'])} added entries")
+
+    return breaking
+
+
+def main():
+    parser = argparse.ArgumentParser(description='Diff public API surface between two refs')
+    parser.add_argument('--old', help='Old git ref (tag/commit) -- checks tools/api_checker/history/ first, '
+                       'then falls back to live extraction')
+    parser.add_argument('--new', help='New git ref (default: HEAD unless --new-file is given)')
+    parser.add_argument('--old-file', help='Path to a stored surface JSON file for the "old" side '
+                       '(bypasses git and tools/api_checker/history/ entirely)')
+    parser.add_argument('--new-file', help='Path to a stored surface JSON file for the "new" side '
+                       '(bypasses git and tools/api_checker/history/ entirely)')
+    parser.add_argument('--no-history', action='store_true',
+                       help='Force live extraction even if a matching tools/api_checker/history/<ref>.json '
+                       'exists -- useful to check a stored record is still faithful to a fresh run')
+    parser.add_argument('--allow-format-mismatch', action='store_true',
+                       help='Proceed even if the two surfaces have different format_version (results may '
+                       'be unsound -- the identity algorithm may differ between versions)')
+    parser.add_argument('--header', default='include/nlohmann/json.hpp',
+                       help='Header file to analyze (relative to repo root, live-extraction only)')
+    parser.add_argument('--include', default='include',
+                       help='Include directory (relative to repo root, live-extraction only)')
+    parser.add_argument('--fail-on-breaking', action='store_true',
+                       help='Exit with status 1 if breaking changes are detected')
+
+    args = parser.parse_args()
+
+    if args.old and args.old_file:
+        parser.error('--old and --old-file are mutually exclusive')
+    if not args.old and not args.old_file:
+        parser.error('one of --old or --old-file is required')
+    if args.new and args.new_file:
+        parser.error('--new and --new-file are mutually exclusive')
+
+    new_ref = args.new or ('HEAD' if not args.new_file else None)
+
+    print(f"Resolving old surface ({args.old_file or args.old})...")
+    old_surface, old_desc = resolve_surface(args.old, args.old_file, args.header, args.include, args.no_history)
+
+    print(f"Resolving new surface ({args.new_file or new_ref})...")
+    new_surface, new_desc = resolve_surface(new_ref, args.new_file, args.header, args.include, args.no_history)
+
+    old_fmt = old_surface.get('format_version')
+    new_fmt = new_surface.get('format_version')
+    # Check both surfaces against SURFACE_FORMAT_VERSION (what *this build* of diff_api.py
+    # understands), not just against each other: two surfaces on the same format_version could
+    # still both be on a version this build predates and doesn't correctly interpret.
+    mismatched = old_fmt != SURFACE_FORMAT_VERSION or new_fmt != SURFACE_FORMAT_VERSION
+    if mismatched and not args.allow_format_mismatch:
+        print(f"Error: format_version mismatch. This build of diff_api.py understands "
+              f"format_version {SURFACE_FORMAT_VERSION!r}, but {old_desc} is {old_fmt!r} and "
+              f"{new_desc} is {new_fmt!r}.")
+        print("The identity/signature algorithm may differ between these two surfaces, making a diff unsound.")
+        print("Re-run with --allow-format-mismatch to proceed anyway.")
+        sys.exit(1)
+    elif mismatched:
+        print(f"WARNING: proceeding with mismatched format_version (this build understands "
+              f"{SURFACE_FORMAT_VERSION!r}; {old_desc}={old_fmt!r}, {new_desc}={new_fmt!r}) as requested.")
+
+    old_api = build_identity_dict(old_surface['public_api'])
+    new_api = build_identity_dict(new_surface['public_api'])
+
+    print(f"\nComparing {len(old_api)} old entries with {len(new_api)} new entries...")
+    diff = diff_surfaces(old_api, new_api)
+
+    breaking = print_diff(diff, old_desc, new_desc)
+
+    if args.fail_on_breaking and breaking:
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    main()

tools/api_checker/extract_api.py

@@ -0,0 +1,668 @@
+#!/usr/bin/env python3
+"""Extract the public API surface of nlohmann/json using libclang AST.
+
+This tool derives the public API from C++ semantics (class templates, access specifiers,
+namespace scoping) independently of documentation status. The extracted surface is the
+source of truth for what is considered "public API" — doc-checking and API diffing are
+downstream consumers of this snapshot.
+
+Strategy:
+1. Parse include/nlohmann/json.hpp with libclang (with proper system includes)
+2. Walk the primary class-template definitions of the 6 known public classes
+3. Extract callable members (methods, constructors, destructors, conversion ops) and type aliases
+4. Extract free functions/operators in nlohmann:: (excluding detail::)
+5. Handle alias-exposed exception types by following the alias to the detail:: definition
+6. Normalize away the ABI inline-namespace (json_abi_v3_12_0, json_abi_diag_v3_12_0, etc.)
+7. Emit a snapshot with an overload-disambiguating identity key and documentation status
+
+Output includes both public_api (all tracked public entities) and documented_non_public
+(entities with @sa comments that are NOT in the public surface — used for validation).
+"""
+
+import argparse
+import json
+import os
+import re
+import subprocess
+import sys
+
+try:
+    from clang import cindex
+except ImportError:
+    print("Error: libclang not installed. Run: pip install -r tools/api_checker/requirements.txt")
+    sys.exit(1)
+
+
+ABI_TAG_PATTERN = re.compile(r'::json(?:_abi)?[a-z_]*_v\d+_\d+_\d+(?=::|$)')
+
+# Bump whenever a change to this schema, or to the identity-computing algorithm
+# (get_signature_text()/get_identity_name()/identity_key()), could alter the 'signature' or
+# 'identity_name' text for otherwise-unchanged source. diff_api.py refuses by default to compare
+# two surface files with different SURFACE_FORMAT_VERSION -- see diff_api.py and
+# tools/api_checker/POLICY.md for why: an earlier, unversioned identity scheme (based on
+# libclang's USR) silently corrupted every historical comparison whenever the *unrelated*
+# enclosing class template gained a new template parameter, and nothing caught it because there
+# was no version to check.
+SURFACE_FORMAT_VERSION = 3
+
+
+def strip_abi_tag(text: str) -> str:
+    """Remove ABI inline-namespace from a qualified name or type string."""
+    return ABI_TAG_PATTERN.sub('', text)
+
+
+_FILE_CONTENT_CACHE = {}
+
+
+def _read_file_cached(path: str) -> str:
+    if path not in _FILE_CONTENT_CACHE:
+        try:
+            with open(path, 'r', encoding='utf-8', errors='ignore') as f:
+                _FILE_CONTENT_CACHE[path] = f.read()
+        except OSError:
+            _FILE_CONTENT_CACHE[path] = ''
+    return _FILE_CONTENT_CACHE[path]
+
+
+def get_signature_text(cursor) -> str:
+    """The normalized source text of a declaration's own signature -- template header, return
+    type, name, full parameter list, and trailing cv/ref/noexcept qualifiers -- stopping before
+    the function body ('{') or at the terminating ';'/'= default;'/'= 0;'. Never includes the
+    body, so implementation-only changes don't affect identity.
+
+    Reads raw source text via cursor.extent's byte offsets rather than cursor.get_tokens():
+    the latter was found to silently return zero tokens whenever a cursor's extent starts
+    exactly at an unexpanded macro invocation (confirmed empirically for basic_json's four
+    binary() overloads and iterator_wrapper(), both preceded by JSON_HEDLEY_WARN_UNUSED_RESULT
+    -- a known class of libclang tokenizer edge case, not specific to this codebase). Raw text
+    also avoids cursor.get_arguments()/cursor.type.spelling, which were separately found
+    empty/unreliable for some FUNCTION_TEMPLATE cursors with complex trailing
+    noexcept(noexcept(...))/decltype(...) clauses (adl_serializer::from_json). Source text is
+    what's actually written (declared names like "ValueType", never a resolved
+    "basic_json<T0,...,T10>"), so it's immune to the enclosing class's template arity too --
+    see identity_key()'s docstring for why that matters.
+
+    Comments are stripped while scanning. Without this, a purely cosmetic NOLINT annotation
+    added mid-signature (e.g. `KeyType&& key) // NOLINT(...)`  before the body's '{') would
+    change the captured text -- confirmed empirically via a real nlohmann/json release
+    (v3.11.2 -> v3.11.3 added such NOLINT comments to several ordered_map methods and to
+    basic_json's swap(), with no other change, and diff_api.py reported all of them as
+    "changed overloads").
+    """
+    start = cursor.extent.start
+    end = cursor.extent.end
+    if not start.file:
+        return ''
+    content = _read_file_cached(start.file.name)
+    if not content:
+        return ''
+    raw = content[start.offset:end.offset]
+
+    paren_depth = 0
+    angle_depth = 0
+    seen_param_list_close = False
+    out = []
+    i = 0
+    n = len(raw)
+    while i < n:
+        ch = raw[i]
+        if ch == '/' and i + 1 < n and raw[i + 1] == '/':
+            i = raw.find('\n', i)
+            if i == -1:
+                break
+            continue
+        if ch == '/' and i + 1 < n and raw[i + 1] == '*':
+            end_comment = raw.find('*/', i + 2)
+            i = n if end_comment == -1 else end_comment + 2
+            continue
+        if ch == '{' and paren_depth == 0 and angle_depth == 0:
+            break
+        if ch == ';' and paren_depth == 0 and angle_depth == 0:
+            out.append(ch)
+            break
+        # A bare ':' after the parameter list has closed starts a constructor's
+        # member-initializer-list ("basic_json(...) : m_data(v) { ... }") -- that's
+        # implementation (which members get initialized how), not public signature, so stop
+        # before it. Guarded by seen_param_list_close so this doesn't misfire on a ':' that's
+        # actually part of a preceding "::" scope-resolution token in the return type/params.
+        if (ch == ':' and seen_param_list_close and paren_depth == 0 and angle_depth == 0
+                and (i == 0 or raw[i - 1] != ':') and (i + 1 >= n or raw[i + 1] != ':')):
+            break
+        if ch == '(':
+            paren_depth += 1
+        elif ch == ')':
+            paren_depth = max(0, paren_depth - 1)
+            if paren_depth == 0:
+                seen_param_list_close = True
+        elif ch == '<':
+            angle_depth += 1
+        elif ch == '>' and angle_depth > 0:
+            angle_depth -= 1
+        out.append(ch)
+        i += 1
+
+    sig = re.sub(r'\s+', ' ', ''.join(out)).strip()
+    return strip_abi_tag(sig)
+
+
+def get_identity_name(cursor, scope: str) -> str:
+    """The name component of a cursor's identity -- usually cursor.spelling, but not for
+    CONSTRUCTOR/DESTRUCTOR cursors, FUNCTION_TEMPLATE cursors that are themselves templated
+    constructors (e.g. `template<typename CompatibleType> basic_json(CompatibleType&& val)`,
+    which libclang represents as FUNCTION_TEMPLATE, not CONSTRUCTOR), or CONVERSION_FUNCTION
+    cursors.
+
+    libclang's cursor.spelling for a constructor-like cursor renders the *enclosing class's full
+    template argument list* (e.g. "basic_json<ObjectType, ..., CustomBaseClass>"), not just
+    "basic_json". Using it as-is for identity would reintroduce class-arity sensitivity (see
+    identity_key()'s docstring for why that's a problem) just for constructors specifically.
+    Detected by checking whether cursor.spelling equals or starts with "<ClassName><" -- the
+    class's own bare name, the last segment of scope. A canonical placeholder
+    ("(constructor)"/"(destructor)") is substituted for identity purposes; callers still use
+    cursor.spelling as-is for human-readable display fields (name/pretty_signature), where the
+    full templated name is informative rather than noisy.
+
+    For CONVERSION_FUNCTION cursors, cursor.spelling renders libclang's internally-resolved
+    return type rather than what's literally written -- confirmed empirically for
+    `json_pointer::operator string_t()` (return type declared via `using string_t = typename
+    string_t_helper<RefStringType>::type`), which spelled as
+    "operator nlohmann::json_pointer::string_t_helper<type-parameter-0-0>::type" locally but
+    "operator typename string_t_helper<type-parameter-0-0>::type" in CI, purely a difference in
+    how each libclang build canonicalizes the same dependent type -- both machines pinned the
+    identical libclang==18.1.1 wheel, and the discrepancy persisted even under a full C++20
+    parse with real <ranges> support, ruling out JSON_HAS_RANGES as the cause. Extracted from
+    raw source text instead (the same "read what's actually written" fix get_signature_text()
+    already applies to signatures generally), via a regex over the cursor's own source extent:
+    immune to libclang's dependent-type resolution differences, and incidentally more readable
+    than "operator type-parameter-1-0" (basic_json's own conversion operator's spelling, which
+    was already an unrelated but analogous artifact worth avoiding here too).
+    """
+    class_bare_name = scope.rsplit('::', 1)[-1]
+    is_constructor_like = (
+        cursor.kind == cindex.CursorKind.CONSTRUCTOR
+        or (cursor.kind == cindex.CursorKind.FUNCTION_TEMPLATE
+            and (cursor.spelling == class_bare_name or cursor.spelling.startswith(class_bare_name + '<')))
+    )
+    if is_constructor_like:
+        return '(constructor)'
+    if cursor.kind == cindex.CursorKind.DESTRUCTOR:
+        return '(destructor)'
+    if cursor.kind == cindex.CursorKind.CONVERSION_FUNCTION or cursor.spelling.startswith('operator '):
+        # The `cursor.spelling.startswith('operator ')` half of this condition also catches
+        # templated conversion operators, which libclang represents as FUNCTION_TEMPLATE rather
+        # than CONVERSION_FUNCTION -- e.g. basic_json's `operator ValueType()`, whose
+        # cursor.spelling is the equally libclang-internal "operator type-parameter-1-0".
+        match = re.search(r'\boperator\s+(.+?)\s*\(\s*\)', get_signature_text(cursor))
+        if match:
+            return f'operator {match.group(1)}'
+    return cursor.spelling
+
+
+def identity_key(cursor, scope: str) -> str:
+    """A stable, overload-disambiguating key, used internally during extraction to prevent two
+    distinct entries from silently colliding in the in-memory api_dict. Two prior approaches were
+    tried and found broken:
+
+    1. {scope, name, kind, params} from cursor.get_arguments() alone: silently collided for
+       overload sets differentiated only by constness, ref-qualifiers, or SFINAE constraints
+       rather than parameter types -- e.g. basic_json's two zero-argument get() overloads (one
+       const, one not) both produced params=[] and overwrote each other in the output dict. A
+       full scan found 59 such silent overwrites across 27 colliding names. Extending this
+       approach with is_const/is_static/ref-qualifier flags fixed most of these but not all --
+       adl_serializer::from_json's two overloads and basic_json's two erase(iterator) overloads
+       still collided, because get_arguments() returns [] for them (see get_signature_text()'s
+       docstring) and their template-parameter lists happen to read identically too.
+    2. libclang's USR: correctly disambiguates every overload (it encodes the full mangled
+       signature) but also encodes the *enclosing class template's own arity* into every
+       member's USR. Confirmed empirically: basic_json gaining a defaulted CustomBaseClass
+       template parameter between v3.11.2 and v3.11.3 (a backward-compatible change) changed
+       literally every basic_json member's USR, which made diff_api.py report ~228/330 entries
+       as "changed" for a release with zero real breaking changes among them. Reconstructing
+       "the member's own identity" by string-surgery on USR text was rejected: clang's USR
+       grammar is undocumented and not a stable contract for this kind of manipulation.
+
+    This key avoids both failure modes: scope is passed in (derived from get_qualified_name(),
+    never from USR), and get_signature_text() reads the declaration as literally written in
+    source, which never encodes the enclosing class's resolved template arguments and reliably
+    disambiguates every case found so far (SFINAE-only overloads, overloads get_arguments()
+    can't see, and simple parameter-type differences alike).
+
+    Known limitation: because the signature text includes parameter *names*, not just types, a
+    pure parameter rename (no type/constraint change) would look like a "changed" entry to
+    diff_api.py. Accepted as a much smaller and rarer source of noise than either bug above --
+    see POLICY.md.
+
+    NOTE: this opaque joined string is only used as a dict key during extraction. The persisted
+    --surface-output format (see main()) stores scope/identity_name/kind/signature as separate,
+    explicit fields instead -- a human or `git diff` should never need to decode this string.
+    """
+    return '\x1f'.join([scope, get_identity_name(cursor, scope), cursor.kind.name, get_signature_text(cursor)])
+
+
+def get_repo_root():
+    """Find the repository root via git, so location paths are deterministic regardless of invoking CWD."""
+    try:
+        result = subprocess.run(
+            ['git', 'rev-parse', '--show-toplevel'],
+            capture_output=True, text=True, check=True, timeout=10
+        )
+        return result.stdout.strip()
+    except (subprocess.CalledProcessError, FileNotFoundError, subprocess.TimeoutExpired):
+        return None
+
+
+REPO_ROOT = get_repo_root()
+
+
+def canonicalize_path(file_path: str) -> str:
+    """Make a file path deterministic: absolute, then relative to the repo root."""
+    if not file_path:
+        return 'unknown'
+    abs_path = os.path.abspath(file_path)
+    if REPO_ROOT:
+        return os.path.relpath(abs_path, REPO_ROOT)
+    return abs_path
+
+
+def cursor_location(cursor) -> str:
+    """Build a canonical 'path:line' string for a cursor, or 'unknown' if it has no file."""
+    if cursor.location and cursor.location.file:
+        return f"{canonicalize_path(cursor.location.file.name)}:{cursor.location.line}"
+    return "unknown"
+
+
+def get_system_includes(compiler='clang++'):
+    """Discover system include paths by parsing clang++ -E -x c++ -v /dev/null output."""
+    try:
+        result = subprocess.run(
+            [compiler, '-E', '-x', 'c++', '-v', '/dev/null'],
+            capture_output=True, text=True, check=True, timeout=10
+        )
+    except (subprocess.CalledProcessError, FileNotFoundError, subprocess.TimeoutExpired) as e:
+        print(f"Warning: Failed to discover system includes via '{compiler}': {e}")
+        return []
+
+    stderr = result.stderr
+    in_block = False
+    paths = []
+    for line in stderr.splitlines():
+        if line.strip() == '#include <...> search starts here:':
+            in_block = True
+            continue
+        if line.strip() == 'End of search list.':
+            in_block = False
+            continue
+        if in_block:
+            # Strip trailing annotations like "(framework directory)"
+            path = line.strip().split()[0] if line.strip() else ''
+            if path:
+                paths.append(path)
+
+    return [f'-isystem{p}' for p in paths]
+
+
+def setup_libclang():
+    """Locate and set up libclang library."""
+    possible_paths = [
+        '/opt/homebrew/opt/llvm/lib/libclang.dylib',  # macOS
+        '/usr/local/opt/llvm/lib/libclang.dylib',      # macOS alt
+        '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libclang.dylib',
+        '/usr/lib/libclang.so',  # Linux
+        '/usr/lib/x86_64-linux-gnu/libclang.so',       # Linux
+    ]
+
+    for path in possible_paths:
+        if os.path.exists(path):
+            try:
+                cindex.conf.set_library_file(path)
+                return True
+            except Exception:
+                continue
+
+    try:
+        filename = cindex.conf.get_filename()
+        if filename:
+            cindex.conf.set_library_file(filename)
+            return True
+    except Exception:
+        pass
+
+    return False
+
+
+def extract_sa_url(raw_comment: str) -> str | None:
+    """Extract @sa URL from a Doxygen comment."""
+    if not raw_comment:
+        return None
+    match = re.search(r'@sa\s+(https://[^\s]+)', raw_comment)
+    return match.group(1) if match else None
+
+
+def get_qualified_name(cursor) -> str:
+    """Get fully qualified name by walking semantic_parent chain."""
+    parts = []
+    c = cursor
+    while c and c.kind != cindex.CursorKind.TRANSLATION_UNIT:
+        if c.kind == cindex.CursorKind.NAMESPACE:
+            # Skip ABI inline-namespace cursors
+            if not ABI_TAG_PATTERN.search(f'::{c.spelling}'):
+                parts.append(c.spelling)
+        elif c.spelling:
+            parts.append(c.spelling)
+        c = c.semantic_parent
+    return '::'.join(reversed(parts)) if parts else ''
+
+
+def walk_class_template(cursor, public_classes: set, api_dict: dict, documented_non_public: list):
+    """Walk a class template's members: extract public callable/type-tier entities, and flag
+    any non-public member that surprisingly carries a real @sa URL (a genuine documentation leak)."""
+    if cursor.kind not in (cindex.CursorKind.CLASS_TEMPLATE, cindex.CursorKind.CLASS_DECL, cindex.CursorKind.STRUCT_DECL):
+        return
+    if cursor.spelling not in public_classes or not cursor.is_definition():
+        return
+
+    scope = strip_abi_tag(get_qualified_name(cursor))
+    location = cursor_location(cursor)
+
+    # Exemption list: STL-container-named-requirement aliases that don't require @sa
+    stl_exempt = {'value_type', 'reference', 'const_reference', 'pointer', 'const_pointer',
+                  'iterator', 'const_iterator', 'reverse_iterator', 'const_reverse_iterator',
+                  'difference_type', 'size_type', 'allocator_type', 'key_type', 'mapped_type'}
+
+    for child in cursor.get_children():
+        is_public = not hasattr(child, 'access_specifier') or str(child.access_specifier) == 'AccessSpecifier.PUBLIC'
+
+        if not is_public:
+            # documented_non_public tracks entities NOT part of the public surface that
+            # nonetheless carry a real @sa URL -- a genuine documentation leak, not "any
+            # public member missing @sa" (that's what check_docs.py's missing-@sa check is for).
+            leaked_url = extract_sa_url(child.raw_comment)
+            if leaked_url:
+                documented_non_public.append({
+                    'location': cursor_location(child),
+                    'raw_comment_excerpt': (child.raw_comment or '')[:100],
+                    'reason': f'{child.kind.name} "{child.spelling}" is non-public but has @sa: {leaked_url}'
+                })
+            continue
+
+        # Callable tier: methods, constructors, destructors, conversion ops, function templates
+        if child.kind in (cindex.CursorKind.CXX_METHOD, cindex.CursorKind.CONSTRUCTOR,
+                         cindex.CursorKind.DESTRUCTOR, cindex.CursorKind.CONVERSION_FUNCTION,
+                         cindex.CursorKind.FUNCTION_TEMPLATE):
+            key = identity_key(child, scope)
+            doc_url = extract_sa_url(child.raw_comment)
+            api_dict[key] = {
+                'scope': scope,
+                'name': child.spelling,
+                'identity_name': get_identity_name(child, scope),
+                'kind': child.kind.name,
+                'tier': 'callable',
+                'signature': get_signature_text(child),
+                'location': cursor_location(child),
+                'doc_url': doc_url,
+                'has_sa': doc_url is not None,
+                'pretty_signature': f"{scope}::{child.spelling}",
+            }
+
+        # Type tier: TYPE_ALIAS_DECL
+        elif child.kind == cindex.CursorKind.TYPE_ALIAS_DECL:
+            name = child.spelling
+            tier = 'type_exempt' if name in stl_exempt else 'type'
+
+            # Try to follow the alias to find @sa on the underlying declaration
+            doc_url = extract_sa_url(child.raw_comment)
+            underlying_location = None
+            if not doc_url and hasattr(child, 'underlying_typedef_type'):
+                try:
+                    underlying_decl = child.underlying_typedef_type.get_declaration()
+                    if underlying_decl and underlying_decl.raw_comment:
+                        doc_url = extract_sa_url(underlying_decl.raw_comment)
+                        if underlying_decl.location.file:
+                            underlying_location = cursor_location(underlying_decl)
+                except Exception:
+                    pass
+
+            key = identity_key(child, scope)
+            api_dict[key] = {
+                'scope': scope,
+                'name': name,
+                'identity_name': get_identity_name(child, scope),
+                'kind': 'TYPE_ALIAS_DECL',
+                'tier': tier,
+                'signature': get_signature_text(child),
+                'location': location,
+                'doc_url': doc_url,
+                'has_sa': doc_url is not None,
+                'pretty_signature': f"{scope}::{name}",
+            }
+            if underlying_location:
+                api_dict[key]['resolved_via_alias_to'] = underlying_location
+
+
+def walk_ast(cursor, public_classes: set, api_dict: dict, documented_non_public: list):
+    """Recursively walk AST."""
+    # Check if this is one of the six public class templates
+    if cursor.kind in (cindex.CursorKind.CLASS_TEMPLATE, cindex.CursorKind.CLASS_DECL, cindex.CursorKind.STRUCT_DECL):
+        if cursor.spelling in public_classes:
+            walk_class_template(cursor, public_classes, api_dict, documented_non_public)
+
+    # Extract free functions (not nested in a class)
+    elif cursor.kind == cindex.CursorKind.FUNCTION_DECL:
+        # Check it's in nlohmann namespace, not detail/std
+        parent = cursor.semantic_parent
+        if parent and parent.kind == cindex.CursorKind.NAMESPACE:
+            ns_name = parent.spelling
+            if ns_name == 'nlohmann' or (parent.semantic_parent and parent.semantic_parent.kind == cindex.CursorKind.NAMESPACE and
+                                         parent.semantic_parent.spelling == 'nlohmann'):
+                # This is a free function in nlohmann (or a subnamespace like json_literals)
+                if 'detail' not in ns_name and 'std' not in ns_name:
+                    # get_qualified_name(parent), not get_qualified_name(cursor) -- the latter
+                    # would include the function's own name as the last segment (cursor is the
+                    # function itself), producing a bogus scope like "nlohmann::operator==" and
+                    # a doubled pretty_signature "nlohmann::operator==::operator==".
+                    scope = strip_abi_tag(get_qualified_name(parent))
+                    key = identity_key(cursor, scope)
+                    doc_url = extract_sa_url(cursor.raw_comment)
+                    api_dict[key] = {
+                        'scope': scope,
+                        'name': cursor.spelling,
+                        'identity_name': get_identity_name(cursor, scope),
+                        'kind': 'FUNCTION_DECL',
+                        'tier': 'callable',
+                        'signature': get_signature_text(cursor),
+                        'location': cursor_location(cursor),
+                        'doc_url': doc_url,
+                        'has_sa': doc_url is not None,
+                        'pretty_signature': f"{scope}::{cursor.spelling}",
+                    }
+
+    # Recurse into container types
+    for child in cursor.get_children():
+        walk_ast(child, public_classes, api_dict, documented_non_public)
+
+
+def write_surface(api_dict: dict, output_path: str, extracted_from: str, extra_meta: dict | None = None):
+    """Write the minimal, location/doc-independent API surface: a format_version-tagged, sorted
+    list of self-describing records (scope, kind, name, identity_name, tier, signature,
+    pretty_signature) -- no opaque joined key, no location, no doc_url.
+
+    This is the file meant to be committed and diffed release-to-release (see
+    tools/api_checker/README.md and POLICY.md): 'signature'/'identity_name' are the same values
+    identity_key() joins into one opaque string for internal use during extraction, but exposed
+    here as separate fields so the file is self-describing -- a human or `git diff` can see
+    exactly what changed without decoding anything (see identity_key()'s docstring).
+
+    extra_meta lets callers (e.g. snapshot_release.py, writing a per-release historical record)
+    add richer, immutable provenance (ref/commit/generated_at) beyond what a live, repeatedly-
+    regenerated snapshot should carry -- see SURFACE_FORMAT_VERSION's docstring for why the live
+    file deliberately omits a timestamp.
+    """
+    records = [
+        {
+            'scope': entry['scope'],
+            'kind': entry['kind'],
+            'name': entry['name'],
+            'identity_name': entry['identity_name'],
+            'tier': entry['tier'],
+            'signature': entry['signature'],
+            'pretty_signature': entry['pretty_signature'],
+        }
+        for entry in api_dict.values()
+    ]
+    records.sort(key=lambda r: (r['scope'], r['name'], r['kind'], r['signature']))
+
+    meta = {'extracted_from': extracted_from}
+    if extra_meta:
+        meta.update(extra_meta)
+
+    output = {
+        'format_version': SURFACE_FORMAT_VERSION,
+        'meta': meta,
+        'public_api': records,
+    }
+    with open(output_path, 'w') as f:
+        json.dump(output, f, indent=2, sort_keys=True)
+        f.write('\n')
+
+
+def run_self_test():
+    """Test ABI-tag stripping."""
+    tests = [
+        ('nlohmann::json_abi_v3_12_0::basic_json::parse', 'nlohmann::basic_json::parse'),
+        ('nlohmann::json_abi_diag_v3_12_0::basic_json::dump', 'nlohmann::basic_json::dump'),
+        ('nlohmann::json_abi_diag_ldvcmp_v3_11_2::basic_json::get', 'nlohmann::basic_json::get'),
+        # The ABI tag as the *last* segment (no following '::') -- the scope of a free function
+        # whose direct parent is the ABI-tagged namespace itself, e.g. nlohmann::operator==.
+        # A regression: an earlier version of this pattern required a trailing '::' via a
+        # lookahead, so it silently failed to strip exactly this case, and diff_api.py reported
+        # every free comparison operator as removed-and-readded on every ABI-tag version bump.
+        ('nlohmann::json_abi_v3_11_3', 'nlohmann'),
+        # v3.11.0/v3.11.1 used "json_vMAJOR_MINOR_PATCH" (no "_abi" segment) before the tag was
+        # renamed to "json_abi_v..." in v3.11.2. A regression: an earlier version of this pattern
+        # hard-required the literal "_abi" segment, so it silently failed to strip this older
+        # form, making diff_api.py report ~100% of the API as removed-and-readded across
+        # v3.10.5->v3.11.0->v3.11.1->v3.11.2 (confirmed against the real backfilled history).
+        ('nlohmann::json_v3_11_0::basic_json::parse', 'nlohmann::basic_json::parse'),
+    ]
+    for input_str, expected in tests:
+        result = strip_abi_tag(input_str)
+        if result != expected:
+            print(f"FAIL: strip_abi_tag('{input_str}') = '{result}', expected '{expected}'")
+            return False
+    print("Self-test passed: ABI-tag stripping works correctly")
+    return True
+
+
+def main():
+    parser = argparse.ArgumentParser(description='Extract public API surface from nlohmann/json')
+    parser.add_argument('--header', default='include/nlohmann/json.hpp',
+                       help='Path to header file to analyze')
+    parser.add_argument('--include', default='include',
+                       help='Include path for parsing')
+    parser.add_argument('--output', default='api_snapshot.json',
+                       help='Output file for the full API snapshot (includes source location and '
+                            'documentation status -- for check_docs.py; not meant to be committed, '
+                            'since location/doc-link churn would make every regeneration look like '
+                            'an API change)')
+    parser.add_argument('--surface-output', default=None,
+                       help='Output file for the minimal API surface (identity only: scope, name, '
+                            'kind, tier, pretty_signature -- no location or doc_url). This is the '
+                            'file meant to be committed and diffed release-to-release, since it is '
+                            'unaffected by unrelated code motion or documentation-site restructuring.')
+    parser.add_argument('--self-test', action='store_true',
+                       help='Run self-tests and exit')
+    parser.add_argument('--extra-isystem', action='append', default=[],
+                       help='Extra -isystem include path (repeatable)')
+
+    args = parser.parse_args()
+
+    if args.self_test:
+        sys.exit(0 if run_self_test() else 1)
+
+    if not setup_libclang():
+        print("Error: Could not locate libclang library")
+        sys.exit(1)
+
+    if not os.path.exists(args.header):
+        print(f"Error: Header file not found: {args.header}")
+        sys.exit(1)
+
+    print(f"Extracting API from {args.header}...")
+
+    # Discover system includes
+    sys_includes = get_system_includes()
+    if not sys_includes:
+        print("Warning: Could not discover system includes via clang++")
+
+    # Build parse arguments
+    parse_args = [
+        f'-I{args.include}',
+        '-std=c++17',
+        '-x', 'c++',
+        '-fparse-all-comments',
+        # JSON_HAS_RANGES auto-detects via the standard library's __cpp_lib_ranges feature-test
+        # macro, which -- unlike compiler-level feature macros such as
+        # __cpp_impl_three_way_comparison -- isn't reliably gated to C++20 mode by every stdlib:
+        # confirmed empirically that it's undefined under -std=c++17 with macOS's libc++, but
+        # defined under the same flag with the Ubuntu stdlib used in CI, producing a different
+        # extracted signature for parse()/accept()/from_*() depending only on which machine ran
+        # the extraction. Pinning to 1 was tried first and rejected: under a real -std=c++17
+        # build, <ranges>'s std::ranges namespace isn't necessarily populated even when the
+        # feature-test macro leaks through, and JSON_HAS_RANGES=1 code paths reference
+        # std::ranges directly, which fails to parse ("no member named 'ranges' in namespace
+        # 'std'") on macOS's libc++ despite the successful C++20 compile above. 0 is the value
+        # that's guaranteed to parse on every stdlib under -std=c++17, so it's the deterministic,
+        # safe choice, even though it means the SentinelType-taking overloads aren't captured.
+        '-DJSON_HAS_RANGES=0',
+    ] + sys_includes + [f'-isystem{path}' for path in args.extra_isystem]
+
+    # Parse
+    index = cindex.Index.create()
+    tu = index.parse(args.header, parse_args,
+                    options=cindex.TranslationUnit.PARSE_DETAILED_PROCESSING_RECORD)
+
+    # Check for errors
+    errors = [d for d in tu.diagnostics if d.severity >= cindex.Diagnostic.Error]
+    if errors:
+        print("Parse errors encountered:")
+        for diag in errors[:10]:
+            print(f"  {diag}")
+        if len(errors) > 10:
+            print(f"  ... and {len(errors) - 10} more")
+        sys.exit(1)
+
+    # Extract API
+    public_classes = {'basic_json', 'adl_serializer', 'byte_container_with_subtype',
+                     'json_pointer', 'json_sax', 'ordered_map'}
+    api_dict = {}
+    documented_non_public = []
+
+    walk_ast(tu.cursor, public_classes, api_dict, documented_non_public)
+
+    # Output. Deliberately no timestamp here: this file is meant to be committed and diffed
+    # (see tools/api_checker/README.md), so its content must be a pure function of the source
+    # tree -- a generated-at timestamp would make every regeneration look like a diff.
+    output = {
+        'meta': {
+            'extracted_from': canonicalize_path(os.path.abspath(args.header)),
+        },
+        'public_api': api_dict,
+        'documented_non_public': documented_non_public,
+    }
+
+    with open(args.output, 'w') as f:
+        json.dump(output, f, indent=2, sort_keys=True)
+        f.write('\n')
+
+    print(f"Found {len(api_dict)} public API entries")
+    if documented_non_public:
+        print(f"Found {len(documented_non_public)} entities with @sa outside the public surface")
+    print(f"Wrote API snapshot to {args.output}")
+
+    if args.surface_output:
+        write_surface(api_dict, args.surface_output, canonicalize_path(os.path.abspath(args.header)))
+        print(f"Wrote API surface (location/doc-independent) to {args.surface_output}")
+
+
+if __name__ == '__main__':
+    main()