Document options to reduce compile times

Add an integration page that collects the ways to reduce compile times with measurements: json_fwd.hpp in headers, JSON_NO_AUTOMATIC_UDLS, explicit instantiation with extern template, modules, and precompiled headers, and notes that JSON_NO_IO and JSON_USE_GLOBAL_UDLS have no measurable effect. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Fix CI: include cycle, GCC 4.8 literal operator spacing, and global UDLs off in the JSON_NO_AUTOMATIC_UDLS test
2026-09-29 19:20:30 +00:00 · 2026-09-29 16:41:53 +02:00 · 2026-09-29 16:40:12 +02:00 · 2026-09-28 22:22:15 +02:00 · 2026-09-28 21:49:37 +02:00 · 2026-09-28 21:24:40 +02:00
40 changed files with 671 additions and 4797 deletions
@@ -67,6 +67,7 @@ jobs:

          python3 $TOOL_DIR/amalgamate.py -c $TOOL_DIR/config_json.json -s .
          python3 $TOOL_DIR/amalgamate.py -c $TOOL_DIR/config_json_fwd.json -s .
+          cp include/nlohmann/json_literals.hpp $INCLUDE_DIR/json_literals.hpp

          # the header list of the Bazel "json" target must match the files in include/
          cmake -P cmake/scripts/gen_bazel_build_file.cmake
@@ -65,6 +65,7 @@ cc_library(
        "include/nlohmann/detail/value_t.hpp",
        "include/nlohmann/json.hpp",
        "include/nlohmann/json_fwd.hpp",
+        "include/nlohmann/json_literals.hpp",
        "include/nlohmann/ordered_map.hpp",
        "include/nlohmann/thirdparty/hedley/hedley.hpp",
        "include/nlohmann/thirdparty/hedley/hedley_undef.hpp",
@@ -21,6 +21,8 @@ TESTS_SRCS=$(shell find tests -type f \( -name '*.hpp' -o -name '*.cpp' -o -name
 # the single headers (amalgamated from the source files)
 AMALGAMATED_FILE=single_include/nlohmann/json.hpp
 AMALGAMATED_FWD_FILE=single_include/nlohmann/json_fwd.hpp
+# json_literals.hpp only includes <nlohmann/json.hpp>, so it is copied verbatim
+AMALGAMATED_LITERALS_FILE=single_include/nlohmann/json_literals.hpp


 ##########################################################################
@@ -29,7 +31,7 @@ AMALGAMATED_FWD_FILE=single_include/nlohmann/json_fwd.hpp

 # main target
 all:
-	@echo "amalgamate - amalgamate files single_include/nlohmann/json{,_fwd}.hpp from the include/nlohmann sources"
+	@echo "amalgamate - amalgamate files single_include/nlohmann/json{,_fwd,_literals}.hpp from the include/nlohmann sources"
 	@echo "BUILD.bazel - regenerate the Bazel BUILD file from the include/nlohmann sources"
 	@echo "ChangeLog.md - generate ChangeLog file"
 	@echo "check-amalgamation - check whether sources have been amalgamated and BUILD.bazel is up to date"
@@ -154,14 +156,14 @@ install_astyle:

 # call the Artistic Style pretty printer on all source files
 pretty: install_astyle
-	$(ASTYLE) --project=tools/astyle/.astylerc $(SRCS) $(TESTS_SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) docs/mkdocs/docs/examples/*.cpp
+	$(ASTYLE) --project=tools/astyle/.astylerc $(SRCS) $(TESTS_SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_LITERALS_FILE) docs/mkdocs/docs/examples/*.cpp

 # call the Clang-Format on all source files
 pretty_format:
 	for FILE in $(SRCS) $(TESTS_SRCS) $(AMALGAMATED_FILE) docs/mkdocs/docs/examples/*.cpp; do echo $$FILE; clang-format -i $$FILE; done

 # create single header files and pretty print
-amalgamate: $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE)
+amalgamate: $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_LITERALS_FILE)
 	$(MAKE) pretty

 # call the amalgamation tool for json.hpp
@@ -172,16 +174,23 @@ $(AMALGAMATED_FILE): $(SRCS)
 $(AMALGAMATED_FWD_FILE): $(SRCS)
 	tools/amalgamate/amalgamate.py -c tools/amalgamate/config_json_fwd.json -s . --verbose=yes

+# copy json_literals.hpp
+$(AMALGAMATED_LITERALS_FILE): include/nlohmann/json_literals.hpp
+	cp include/nlohmann/json_literals.hpp $(AMALGAMATED_LITERALS_FILE)
+
 # check if file single_include/nlohmann/json.hpp has been amalgamated from the nlohmann sources
 # Note: this target is called by Travis
 check-amalgamation:
 	@mv $(AMALGAMATED_FILE) $(AMALGAMATED_FILE)~
 	@mv $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_FWD_FILE)~
+	@mv $(AMALGAMATED_LITERALS_FILE) $(AMALGAMATED_LITERALS_FILE)~
 	@$(MAKE) amalgamate
 	@diff $(AMALGAMATED_FILE) $(AMALGAMATED_FILE)~ || (echo "===================================================================\n  Amalgamation required! Please read the contribution guidelines\n  in file .github/CONTRIBUTING.md.\n===================================================================" ; mv $(AMALGAMATED_FILE)~ $(AMALGAMATED_FILE) ; false)
 	@diff $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_FWD_FILE)~ || (echo "===================================================================\n  Amalgamation required! Please read the contribution guidelines\n  in file .github/CONTRIBUTING.md.\n===================================================================" ; mv $(AMALGAMATED_FWD_FILE)~ $(AMALGAMATED_FWD_FILE) ; false)
+	@diff $(AMALGAMATED_LITERALS_FILE) $(AMALGAMATED_LITERALS_FILE)~ || (echo "===================================================================\n  Amalgamation required! Please read the contribution guidelines\n  in file .github/CONTRIBUTING.md.\n===================================================================" ; mv $(AMALGAMATED_LITERALS_FILE)~ $(AMALGAMATED_LITERALS_FILE) ; false)
 	@mv $(AMALGAMATED_FILE)~ $(AMALGAMATED_FILE)
 	@mv $(AMALGAMATED_FWD_FILE)~ $(AMALGAMATED_FWD_FILE)
+	@mv $(AMALGAMATED_LITERALS_FILE)~ $(AMALGAMATED_LITERALS_FILE)
 	@mv BUILD.bazel BUILD.bazel~
 	@$(MAKE) BUILD.bazel
 	@diff BUILD.bazel BUILD.bazel~ || (echo "===================================================================\n  BUILD.bazel is out of date! Please run 'make BUILD.bazel'.\n===================================================================" ; mv BUILD.bazel~ BUILD.bazel ; false)
@@ -222,7 +231,7 @@ json.tar.xz:
 # We use `-X` to make the resulting ZIP file reproducible, see
 # <https://content.pivotal.io/blog/barriers-to-deterministic-reproducible-zip-files>.
 include.zip: BUILD.bazel
-	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) BUILD.bazel MODULE.bazel meson.build LICENSE.MIT
+	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_LITERALS_FILE) BUILD.bazel MODULE.bazel meson.build LICENSE.MIT

 # Create the files for a release and add signatures and hashes.
 release: include.zip json.tar.xz
@@ -231,10 +240,12 @@ release: include.zip json.tar.xz
 	gpg --armor --detach-sig include.zip
 	gpg --armor --detach-sig $(AMALGAMATED_FILE)
 	gpg --armor --detach-sig $(AMALGAMATED_FWD_FILE)
+	gpg --armor --detach-sig $(AMALGAMATED_LITERALS_FILE)
 	gpg --armor --detach-sig json.tar.xz
 	cp $(AMALGAMATED_FILE) release_files
 	cp $(AMALGAMATED_FWD_FILE) release_files
-	mv $(AMALGAMATED_FILE).asc $(AMALGAMATED_FWD_FILE).asc json.tar.xz json.tar.xz.asc include.zip include.zip.asc release_files
+	cp $(AMALGAMATED_LITERALS_FILE) release_files
+	mv $(AMALGAMATED_FILE).asc $(AMALGAMATED_FWD_FILE).asc $(AMALGAMATED_LITERALS_FILE).asc json.tar.xz json.tar.xz.asc include.zip include.zip.asc release_files
 	cd release_files ; shasum -a 256 json.hpp include.zip json.tar.xz > hashes.txt


@@ -373,9 +373,10 @@ file(GLOB_RECURSE INDENT_FILES
 set(include_dir ${PROJECT_SOURCE_DIR}/single_include/nlohmann)
 set(tool_dir ${PROJECT_SOURCE_DIR}/tools/amalgamate)
 add_custom_target(ci_test_amalgamation
-    COMMAND rm -fr ${include_dir}/json.hpp~ ${include_dir}/json_fwd.hpp~
+    COMMAND rm -fr ${include_dir}/json.hpp~ ${include_dir}/json_fwd.hpp~ ${include_dir}/json_literals.hpp~
    COMMAND cp ${include_dir}/json.hpp ${include_dir}/json.hpp~
    COMMAND cp ${include_dir}/json_fwd.hpp ${include_dir}/json_fwd.hpp~
+    COMMAND cp ${include_dir}/json_literals.hpp ${include_dir}/json_literals.hpp~

    COMMAND ${Python3_EXECUTABLE} -mvenv venv_astyle
    COMMAND venv_astyle/bin/pip3 --quiet install -r ${CMAKE_SOURCE_DIR}/tools/astyle/requirements.txt
@@ -383,10 +384,12 @@ add_custom_target(ci_test_amalgamation

    COMMAND ${Python3_EXECUTABLE} ${tool_dir}/amalgamate.py -c ${tool_dir}/config_json.json -s .
    COMMAND ${Python3_EXECUTABLE} ${tool_dir}/amalgamate.py -c ${tool_dir}/config_json_fwd.json -s .
+    COMMAND cp ${PROJECT_SOURCE_DIR}/include/nlohmann/json_literals.hpp ${include_dir}/json_literals.hpp
    COMMAND venv_astyle/bin/astyle --project=tools/astyle/.astylerc --suffix=none ${include_dir}/json.hpp ${include_dir}/json_fwd.hpp

    COMMAND diff ${include_dir}/json.hpp~ ${include_dir}/json.hpp
    COMMAND diff ${include_dir}/json_fwd.hpp~ ${include_dir}/json_fwd.hpp
+    COMMAND diff ${include_dir}/json_literals.hpp~ ${include_dir}/json_literals.hpp

    COMMAND venv_astyle/bin/astyle --project=tools/astyle/.astylerc --suffix=orig ${INDENT_FILES}
    COMMAND for FILE in `find . -name '*.orig'`\; do false \; done
@@ -28,6 +28,7 @@ header. See also the [macro overview page](../../features/macros.md).
 - [**JSON_HAS_RANGES**](json_has_ranges.md) - control `std::ranges` support
 - [**JSON_HAS_STD_FORMAT**](json_has_std_format.md) - control `std::format`/`std::formatter` support
 - [**JSON_HAS_THREE_WAY_COMPARISON**](json_has_three_way_comparison.md) - control 3-way comparison support
+- [**JSON_NO_AUTOMATIC_UDLS**](json_no_automatic_udls.md) - do not include the user-defined string literals (UDLs) automatically
 - [**JSON_NO_IO**](json_no_io.md) - switch off functions relying on certain C++ I/O headers
 - [**JSON_NO_THREAD_LOCAL**](json_no_thread_local.md) - switch off the use of `thread_local` storage
 - [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](json_skip_unsupported_compiler_check.md) - do not warn about unsupported compilers
@@ -53,8 +54,6 @@ header. See also the [macro overview page](../../features/macros.md).
 - [**JSON_BRACE_INIT_COPY_SEMANTICS**](json_brace_init_copy_semantics.md) - opt in to copy/move semantics for single-element brace initialization
 - [**JSON_DISABLE_ENUM_SERIALIZATION**](json_disable_enum_serialization.md) - switch off default serialization/deserialization functions for enums
 - [**JSON_USE_IMPLICIT_CONVERSIONS**](json_use_implicit_conversions.md) - control implicit conversions
- [**JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS**](json_use_objects_for_enum_keyed_maps.md) - opt in to storing maps with enum
-  keys as objects

 ## Comparison behavior

@@ -0,0 +1,69 @@
+# JSON_NO_AUTOMATIC_UDLS
+
+```cpp
+#define JSON_NO_AUTOMATIC_UDLS
+```
+
+When defined, `<nlohmann/json.hpp>` does not include `<nlohmann/json_literals.hpp>`, so the user-defined string
+literals [`operator""_json`](../operator_literal_json.md) and
+[`operator""_json_pointer`](../operator_literal_json_pointer.md) are not declared. Include
+`<nlohmann/json_literals.hpp>` in the files that use them.
+
+The literals are ordinary inline functions whose bodies call the parser, so every translation unit that includes them
+instantiates the parser — even if it never parses anything itself. Defining `JSON_NO_AUTOMATIC_UDLS` for a whole project
+avoids this cost in translation units that do not parse (e.g., ones that only define types and conversions or pass
+`json` values around) and reduces their compile time.
+
+## Default definition
+
+By default, `#!cpp JSON_NO_AUTOMATIC_UDLS` is not defined, and `<nlohmann/json.hpp>` includes
+`<nlohmann/json_literals.hpp>`.
+
+```cpp
+#undef JSON_NO_AUTOMATIC_UDLS
+```
+
+## Notes
+
+!!! info "Header `<nlohmann/json_literals.hpp>`"
+
+    The header includes `<nlohmann/json.hpp>` itself and places the literals according to
+    [`JSON_USE_GLOBAL_UDLS`](json_use_global_udls.md). It is part of the multi-header sources (`include/nlohmann`)
+    and of the single-header sources (`single_include/nlohmann`), next to `json.hpp`.
+
+!!! info "C++ modules"
+
+    The `nlohmann.json` [module](../../features/modules.md) always exports the literals, regardless of this macro.
+
+## Examples
+
+??? example
+
+    The code below includes the library without the literals and adds them in a single translation unit.
+
+    ```cpp
+    // compiled with -DJSON_NO_AUTOMATIC_UDLS for the whole project
+    #include <nlohmann/json.hpp>
+
+    // this file uses the literals, so it includes them explicitly
+    #include <nlohmann/json_literals.hpp>
+
+    int main()
+    {
+        auto j = R"({"foo": 42})"_json;
+        return j.at("/foo"_json_pointer) == 42 ? 0 : 1;
+    }
+    ```
+
+    Without the include of `<nlohmann/json_literals.hpp>`, the code would fail to compile.
+
+## See also
+
+- [`operator""_json`](../operator_literal_json.md)
+- [`operator""_json_pointer`](../operator_literal_json_pointer.md)
+- [`JSON_USE_GLOBAL_UDLS`](json_use_global_udls.md) - place user-defined string literals (UDLs) into the global namespace
+- [Compile times](../../integration/compile_times.md) - options to reduce compile times
+
+## Version history
+
+- Added in version 3.13.0.
@@ -15,7 +15,7 @@ The default value is `1`.
 #define JSON_USE_GLOBAL_UDLS 1
 ```

-When the macro is not defined, the library will define it to its default value.
+When the macro is not defined, the library behaves as if it were defined to its default value.

 ## Notes

@@ -32,6 +32,11 @@ When the macro is not defined, the library will define it to its default value.
    [`JSON_GlobalUDLs`](../../integration/cmake.md#json_globaludls) (`ON` by default) which defines
    `JSON_USE_GLOBAL_UDLS` accordingly.

+!!! info "Leaving out the literals"
+
+    If [`JSON_NO_AUTOMATIC_UDLS`](json_no_automatic_udls.md) is defined, the literals are only declared where
+    `<nlohmann/json_literals.hpp>` is included; this macro then applies to that header.
+
 ## Examples

 ??? example "Example 1: Default behavior"
@@ -92,6 +97,7 @@ When the macro is not defined, the library will define it to its default value.

 - [`operator""_json`](../operator_literal_json.md)
 - [`operator""_json_pointer`](../operator_literal_json_pointer.md)
+- [`JSON_NO_AUTOMATIC_UDLS`](json_no_automatic_udls.md) - do not include the user-defined string literals automatically
 - [:simple-cmake: JSON_GlobalUDLs](../../integration/cmake.md#json_globaludls) - CMake option to control the macro

 ## Version history
@@ -1,139 +0,0 @@
-# JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-
-```cpp
-#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS /* value */
-```
-
-When defined to `1`, maps whose keys are enums (such as `std::map<E, T>` or `std::unordered_map<E, T>`) are stored as
-JSON objects, using the enum's own conversion for the keys. By default, they are stored as arrays of `[key, value]`
-pairs.
-
-## Default definition
-
-The default value is `0` (disabled — existing behavior is preserved).
-
-```cpp
-#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
-```
-
-## Notes
-
-!!! note "Background"
-
-    JSON object keys are strings, so a map is only stored as an object if its keys can be converted to a string type.
-    Enums are not, even if [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) maps them to strings, so a
-    map with enum keys becomes an array of `[key, value]` pairs:
-
-    ```json
-    [["stopped", "aa"], ["completed", "bb"]]
-    ```
-
-    With this macro, the same map becomes an object
-    (see [#4378](https://github.com/nlohmann/json/issues/4378)):
-
-    ```json
-    {"completed": "bb", "stopped": "aa"}
-    ```
-
-!!! note "Maps with non-unique keys"
-
-    Maps that allow duplicate keys, such as `std::multimap<E, T>` or `std::unordered_multimap<E, T>`, are not affected
-    by the macro and are still stored as arrays of `[key, value]` pairs, as an object cannot hold duplicate keys.
-
-!!! note "Reading"
-
-    Reading is not affected by the macro: a map with enum keys can always be read from both an array of pairs and an
-    object. For the latter, each key is converted to the enum with its `from_json` function, e.g., the one defined by
-    [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md). Data written without the macro can therefore
-    still be read after enabling it.
-
-!!! warning "Keys must serialize to distinct strings"
-
-    Each key is converted with the enum's `to_json` function. If a key is not converted to a string (for instance, an
-    enum without [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md), which is stored as an integer, or an
-    enumerator mapped to `nullptr`), [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) is thrown.
-    If two keys are converted to the same string (for instance, because
-    [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) maps an unlisted enumerator to the first entry),
-    [`type_error.318`](../../home/exceptions.md#jsonexceptiontype_error318) is thrown. In both cases, the target value
-    is not changed.
-
-!!! warning "Opt-in only"
-
-    This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no effect.
-
-!!! note "ABI compatibility"
-
-    The value of this macro is encoded in the [namespace](../../features/namespace.md) (tag `_ekmo`), resulting in
-    distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program
-    without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.
-
-## Examples
-
-??? example "Default behavior (macro not defined)"
-
-    Without the macro, a map with enum keys is stored as an array of pairs:
-
-    ```cpp
-    #include <map>
-    #include <nlohmann/json.hpp>
-
-    using json = nlohmann::json;
-
-    enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
-
-    NLOHMANN_JSON_SERIALIZE_ENUM(TaskState, {
-        {TS_STOPPED, "stopped"},
-        {TS_RUNNING, "running"},
-        {TS_COMPLETED, "completed"},
-    })
-
-    int main()
-    {
-        std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
-
-        json j = m;
-        // j is [["stopped","aa"],["completed","bb"]]
-    }
-    ```
-
-??? example "Objects for enum-keyed maps (macro defined to 1)"
-
-    With the macro, the same map is stored as an object:
-
-    ```cpp
-    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 1
-    #include <map>
-    #include <nlohmann/json.hpp>
-
-    using json = nlohmann::json;
-
-    enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
-
-    NLOHMANN_JSON_SERIALIZE_ENUM(TaskState, {
-        {TS_STOPPED, "stopped"},
-        {TS_RUNNING, "running"},
-        {TS_COMPLETED, "completed"},
-    })
-
-    int main()
-    {
-        std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
-
-        json j = m;
-        // j is {"completed":"bb","stopped":"aa"}
-
-        auto m2 = j.get<std::map<TaskState, std::string>>();
-        // m2 == m
-    }
-    ```
-
-## See also
-
- [Specializing enum conversion](../../features/enum_conversion.md)
- [**NLOHMANN_JSON_SERIALIZE_ENUM**](nlohmann_json_serialize_enum.md) - serialize/deserialize an enum
- [**NLOHMANN_JSON_SERIALIZE_ENUM_STRICT**](nlohmann_json_serialize_enum_strict.md) - serialize/deserialize an enum with
-  exceptions
-
-## Version history
-
- Added in version 3.13.0.
@@ -41,9 +41,6 @@ inline void from_json(const BasicJsonType& j, type& e);
      conversion. Select this default pair carefully. See example 1 below.
    - If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
      list will be returned when converting to or from JSON. See example 2 below.
-    - Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default.
-      Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
-      with the converted keys. Such maps can be read from both forms.

 ## Examples

@@ -83,7 +80,6 @@ inline void from_json(const BasicJsonType& j, type& e);
 - [Specializing enum conversion](../../features/enum_conversion.md)
 - [`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](./nlohmann_json_serialize_enum_strict.md)
 - [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
- [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md)

 ## Version history

@@ -44,9 +44,6 @@ inline void from_json(const BasicJsonType& j, type& e);
      `"enum value out of range for <type>"`.
    - If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
      list will be returned when converting to or from JSON. See example 2 below.
-    - Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default.
-      Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
-      with the converted keys. Such maps can be read from both forms.

 ## Examples

@@ -102,7 +99,6 @@ inline void from_json(const BasicJsonType& j, type& e);
 - [Specializing enum conversion](../../features/enum_conversion.md)
 - [`NLOHMANN_JSON_SERIALIZE_ENUM`](./nlohmann_json_serialize_enum.md)
 - [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
- [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md)

 ## Version history

@@ -18,7 +18,9 @@ using namespace nlohmann;
 ```

 This is suggested to ease migration to the next major version release of the library. See
-[`JSON_USE_GLOBAL_UDLS`](macros/json_use_global_udls.md#notes) for details.
+[`JSON_USE_GLOBAL_UDLS`](macros/json_use_global_udls.md#notes) for details. The operator is declared in header
+`<nlohmann/json_literals.hpp>`, which `<nlohmann/json.hpp>` includes unless
+[`JSON_NO_AUTOMATIC_UDLS`](macros/json_no_automatic_udls.md) is defined.

 ## Parameters

@@ -59,6 +61,8 @@ Linear.
 ## See also

 - [Creating JSON values](../features/creating_values.md) - the article on creating JSON values
+- [JSON_NO_AUTOMATIC_UDLS](macros/json_no_automatic_udls.md) - do not include the user-defined string literals
+  automatically

 ## Version history

@@ -17,7 +17,9 @@ using namespace nlohmann::literals::json_literals;
 using namespace nlohmann;
 ```
 This is suggested to ease migration to the next major version release of the library. See
-[`JSON_USE_GLOBAL_UDLS`](macros/json_use_global_udls.md#notes) for details.
+[`JSON_USE_GLOBAL_UDLS`](macros/json_use_global_udls.md#notes) for details. The operator is declared in header
+`<nlohmann/json_literals.hpp>`, which `<nlohmann/json.hpp>` includes unless
+[`JSON_NO_AUTOMATIC_UDLS`](macros/json_no_automatic_udls.md) is defined.

 ## Parameters

@@ -58,6 +60,8 @@ Linear.
 ## See also

 - [json_pointer](json_pointer/index.md) - type to represent JSON Pointers
+- [JSON_NO_AUTOMATIC_UDLS](macros/json_no_automatic_udls.md) - do not include the user-defined string literals
+  automatically

 ## Version history

@@ -43,23 +43,6 @@ json jPi = 3.14;
 assert(jPi.get<TaskState>() == TS_INVALID );
 ```

-## Maps with enum keys
-
-By default, maps with enum keys, such as `std::map<TaskState, std::string>`, are stored as arrays of `[key, value]`
-pairs, because JSON object keys must be strings. Define
-[`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md) before including the
-library to store them as objects, with the keys converted by the enum's `to_json()` function:
-
-```cpp
-std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
-
-json j = m;
-// default:                                   [["stopped","aa"],["completed","bb"]]
-// with JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS: {"completed":"bb","stopped":"aa"}
-```
-
-Either form can be read back, with or without the macro.
-
 ## Notes

 Just as in [Arbitrary Type Conversions](arbitrary_types.md) above,
@@ -83,6 +83,15 @@ When defined, default parse and serialize functions for enums are excluded and h

 See [full documentation of `JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json_disable_enum_serialization.md).

+## `JSON_NO_AUTOMATIC_UDLS`
+
+When defined, `<nlohmann/json.hpp>` does not include `<nlohmann/json_literals.hpp>` with the user-defined string literals
+`operator""_json` and `operator""_json_pointer`. This reduces the compile time of translation units that do not use
+them, because the literals instantiate the parser in every translation unit that includes them. Include
+`<nlohmann/json_literals.hpp>` where the literals are needed.
+
+See [full documentation of `JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md).
+
 ## `JSON_NO_IO`

 When defined, headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostream>` are not included and parse functions
@@ -167,13 +176,6 @@ behavior is deprecated and switched off (`0`) by default.

 See [full documentation of `JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](../api/macros/json_use_legacy_discarded_value_comparison.md).

-## `JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`
-
-When defined to `1`, maps with enum keys (e.g., `std::map<E, T>`) are stored as objects, using the enum's conversion for
-the keys, instead of arrays of `[key, value]` pairs. It is switched off (`0`) by default.
-
-See [full documentation of `JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md).
-
 ## `JSON_USE_SIMDUTF`

 When defined, UTF-8 validation of JSON strings read from contiguous byte input is delegated to the
@@ -40,6 +40,9 @@ Only the following symbols are exported from `nlohmann.json`:
 - `nlohmann::literals::json_literals::operator""_json`
 - `nlohmann::literals::json_literals::operator""_json_pointer`

+The module always exports the two user-defined string literals, even if
+[`JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md) is defined when building it.
+
 Additionally, the following `nlohmann::detail` symbols are exported, solely to work around an MSVC compilation issue
 ([#3970](https://github.com/nlohmann/json/issues/3970)). They are implementation details, not part of the public API,
 and should not be used directly:
@@ -20,8 +20,6 @@ The complete default namespace name is derived as follows:
      `_bics`.
    - [`JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md) defined non-zero appends `_psp`.
    - [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md) defined non-zero appends `_snul`.
-    - [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md) defined non-zero
-      appends `_ekmo`.
 - The inline namespace ends with the suffix `_v` followed by the 3 components of the version number separated by
  underscores. To omit the version component, see [Disabling the version component](#disabling-the-version-component)
  below.
@@ -596,9 +596,6 @@ During implicit or explicit value conversion, the JSON type must be compatible w
    [json.exception.type_error.302] type must be string, but is object
    ```

-This exception is also thrown with [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md)
-if a key of a map with enum keys is not converted to a string, for instance, because the enum is stored as an integer.
-
 ### json.exception.type_error.303

 To retrieve a reference to a value stored in a `basic_json` object with `get_ref`, the type of the reference must match the value type. For instance, for a JSON array, the `ReferenceType` must be `array_t &`.
@@ -785,19 +782,6 @@ The dynamic type of the object cannot be represented in the requested serializat

    Encapsulate the JSON value in an object. That is, instead of serializing `#!json true`, serialize `#!json {"value": true}`

-### json.exception.type_error.318
-
-With [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md), a map with enum
-keys is stored as an object. This exception is thrown if two of its keys are converted to the same string, so one of the
-entries would be lost. This happens, for instance, if [`NLOHMANN_JSON_SERIALIZE_ENUM`](../api/macros/nlohmann_json_serialize_enum.md)
-does not list an enumerator and it is therefore converted like the first listed one.
-
-!!! failure "Example message"
-
-    ```
-    [json.exception.type_error.318] duplicate object key 'red'
-    ```
-
 ## Out of range

 This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance, in the case of array indices or nonexisting object keys.
@@ -0,0 +1,149 @@
+# Compile times
+
+The library is header-only and makes heavy use of templates, so every translation unit that includes
+`<nlohmann/json.hpp>` pays for parsing the header and instantiating what it uses. This page lists the options to reduce
+that cost, ordered by how much they typically save.
+
+!!! info "Measurements"
+
+    The numbers below are medians of nine runs compiling a single translation unit with `-std=c++17 -c` against the
+    single-header version, with Apple clang and GCC 16 on macOS (Apple silicon). They show the order of magnitude to
+    expect; measure your own code before and after a change.
+
+## Include `json_fwd.hpp` in headers
+
+Header files that only need to *name* the `json` type — for function declarations, members held by pointer or
+reference, or friend declarations — can include `<nlohmann/json_fwd.hpp>` instead of `<nlohmann/json.hpp>`. It only
+forward-declares `basic_json`, `json`, `ordered_json`, `json_pointer`, and `adl_serializer`. The translation units that
+actually use the values then include `<nlohmann/json.hpp>`.
+
+```cpp title="person.hpp"
+#pragma once
+#include <nlohmann/json_fwd.hpp>
+
+struct person;
+void to_json(nlohmann::json& j, const person& p);
+void from_json(const nlohmann::json& j, person& p);
+```
+
+```cpp title="person.cpp"
+#include "person.hpp"
+#include <nlohmann/json.hpp>
+
+void to_json(nlohmann::json& j, const person& p) { /* ... */ }
+void from_json(const nlohmann::json& j, person& p) { /* ... */ }
+```
+
+| Compiler    | `json.hpp` (`-O0`) | `json_fwd.hpp` (`-O0`) | Change |
+|-------------|-------------------:|-----------------------:|-------:|
+| Apple clang |             704 ms |                 329 ms |   −53% |
+| GCC 16      |             779 ms |                 242 ms |   −69% |
+
+This is the most effective option, because it avoids the full header in every translation unit that includes
+*your* headers.
+
+## Opt out of the automatic user-defined string literals
+
+The user-defined string literals [`operator""_json`](../api/operator_literal_json.md) and
+[`operator""_json_pointer`](../api/operator_literal_json_pointer.md) are ordinary inline functions whose bodies call the
+parser. As `<nlohmann/json.hpp>` includes them by default, every translation unit instantiates the parser, even if it
+never parses anything itself.
+
+Define [`JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md) for the whole project and include
+`<nlohmann/json_literals.hpp>` only in the files that use the literals:
+
+```cmake
+target_compile_definitions(my_target PRIVATE JSON_NO_AUTOMATIC_UDLS)
+```
+
+```cpp
+#include <nlohmann/json.hpp>
+#include <nlohmann/json_literals.hpp> // only where "..."_json is used
+```
+
+The saving applies to translation units that do not parse JSON, for example ones that define types and their
+conversions or only pass `json` values around:
+
+| Compiler    | Translation unit | Default (`-O0` / `-O2`) | `JSON_NO_AUTOMATIC_UDLS` (`-O0` / `-O2`) | Change      |
+|-------------|------------------|------------------------:|-----------------------------------------:|------------:|
+| Apple clang | model            |         776 ms / 846 ms |                          629 ms / 692 ms | −19% / −18% |
+| GCC 16      | model            |       1022 ms / 1120 ms |                          882 ms / 965 ms | −14% / −14% |
+| Apple clang | parsing          |       992 ms / 1815 ms |                        1006 ms / 1823 ms |   +1% / 0% |
+| GCC 16      | parsing          |      2018 ms / 3420 ms |                        1990 ms / 3454 ms |   −1% / +1% |
+
+Translation units that include only the header save up to a third. Translation units that parse anyway instantiate
+the parser regardless and see no difference.
+
+## Instantiate `basic_json` once
+
+Each translation unit instantiates the member functions of `nlohmann::json` it uses. An explicit instantiation
+declaration tells the compiler that the non-template members are instantiated elsewhere, so it can skip them:
+
+```cpp title="json_instance.hpp"
+#pragma once
+#include <nlohmann/json.hpp>
+
+extern template class nlohmann::basic_json<>;
+```
+
+```cpp title="json_instance.cpp"
+#include "json_instance.hpp"
+
+template class nlohmann::basic_json<>;
+```
+
+Include `json_instance.hpp` instead of `<nlohmann/json.hpp>` and compile and link `json_instance.cpp` once.
+
+| Compiler    | Translation unit    | Default (`-O0` / `-O2`) | `extern template` (`-O0` / `-O2`) | Change      |
+|-------------|---------------------|------------------------:|----------------------------------:|------------:|
+| Apple clang | parsing             |        992 ms / 1815 ms |                  953 ms / 1625 ms |  −4% / −10% |
+| GCC 16      | parsing             |       2018 ms / 3420 ms |                 1522 ms / 2728 ms | −25% / −20% |
+| Apple clang | `json_instance.cpp` |                       — |                 2166 ms / 4660 ms |           — |
+| GCC 16      | `json_instance.cpp` |                       — |                5085 ms / 10616 ms |           — |
+
+Notes:
+
+- The saving grows with the number of translation units that use `json`, while the instantiation translation unit is
+  compiled only once (and is rarely recompiled, as it does not depend on your code).
+- Member function templates (such as `get<T>()`, `parse(InputType&&)`, or `value(key, default)`) are not covered by
+  the explicit instantiation and are still instantiated where they are used.
+- The declaration covers exactly `nlohmann::json`. Add the same lines for `nlohmann::ordered_json`
+  (`nlohmann::basic_json<nlohmann::ordered_map>`) or your own `basic_json` specializations if you use them.
+
+## Use C++20 modules
+
+With a toolchain that supports named modules, `import nlohmann.json;` compiles the library once into a module and
+avoids parsing the header in every translation unit. See [Modules](../features/modules.md) for requirements and known
+issues. Module support is experimental and currently depends heavily on the compiler version.
+
+## Use precompiled headers
+
+Build systems can precompile `<nlohmann/json.hpp>` together with other stable headers, for example with CMake's
+[`target_precompile_headers`](https://cmake.org/cmake/help/latest/command/target_precompile_headers.html):
+
+```cmake
+target_precompile_headers(my_target PRIVATE <nlohmann/json.hpp>)
+```
+
+This removes the cost of parsing the header, but not of instantiating templates in each translation unit, so it
+combines well with the options above.
+
+## Options without effect on compile times
+
+Some configuration macros change what the library declares, but do not measurably change compile times:
+
+| Macro                                                                  | Apple clang, model (`-O0` / `-O2`) | GCC 16, model (`-O0` / `-O2`) |
+|------------------------------------------------------------------------|-----------------------------------:|------------------------------:|
+| default                                                                |                    776 ms / 846 ms |             1022 ms / 1120 ms |
+| [`JSON_NO_IO`](../api/macros/json_no_io.md)                            |                    764 ms / 836 ms |             1022 ms / 1117 ms |
+| [`JSON_USE_GLOBAL_UDLS`](../api/macros/json_use_global_udls.md)`=0`    |                    763 ms / 852 ms |             1019 ms / 1106 ms |
+
+`JSON_USE_GLOBAL_UDLS` only controls *where* the literals are declared; to avoid their cost, use
+`JSON_NO_AUTOMATIC_UDLS` instead.
+
+## See also
+
+- [`JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md) - do not include the user-defined string
+  literals automatically
+- [Modules](../features/modules.md) - C++20 module support
+- [Header only](index.md) - including the library
@@ -15,4 +15,7 @@ Clang).

 You can further use file
 [`single_include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_fwd.hpp)
-for forward declarations.
+for forward declarations (see [Compile times](compile_times.md)), and file
+[`single_include/nlohmann/json_literals.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_literals.hpp)
+for the user-defined string literals if you define
+[`JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md).
@@ -106,6 +106,7 @@ nav:
      - integration/cmake.md
      - integration/package_managers.md
      - integration/pkg-config.md
+      - integration/compile_times.md
  - API Documentation:
      - basic_json:
          - 'Overview': api/basic_json/index.md
@@ -293,6 +294,7 @@ nav:
          - 'JSON_HAS_STATIC_RTTI': api/macros/json_has_static_rtti.md
          - 'JSON_HAS_STD_FORMAT': api/macros/json_has_std_format.md
          - 'JSON_HAS_THREE_WAY_COMPARISON': api/macros/json_has_three_way_comparison.md
+          - 'JSON_NO_AUTOMATIC_UDLS': api/macros/json_no_automatic_udls.md
          - 'JSON_NOEXCEPTION': api/macros/json_noexception.md
          - 'JSON_NO_IO': api/macros/json_no_io.md
          - 'JSON_NO_THREAD_LOCAL': api/macros/json_no_thread_local.md
@@ -303,7 +305,6 @@ nav:
          - 'JSON_USE_GLOBAL_UDLS': api/macros/json_use_global_udls.md
          - 'JSON_USE_IMPLICIT_CONVERSIONS': api/macros/json_use_implicit_conversions.md
          - 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON': api/macros/json_use_legacy_discarded_value_comparison.md
-          - 'JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS': api/macros/json_use_objects_for_enum_keyed_maps.md
          - 'JSON_USE_SIMDUTF': api/macros/json_use_simdutf.md
          - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
          - 'NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_intrusive.md
@@ -46,10 +46,6 @@
    #define JSON_STRICT_NUL_HANDLING 0
 #endif

-#ifndef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
-#endif
-
 #if JSON_DIAGNOSTICS
    #define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
 #else
@@ -86,20 +82,14 @@
    #define NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING
 #endif

-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS _ekmo
-#else
-    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS
-#endif
-
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
    #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif

 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g) json_abi ## a ## b ## c ## d ## e ## f ## g
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g)
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f) json_abi ## a ## b ## c ## d ## e ## f
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f) \
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f)

 #define NLOHMANN_JSON_ABI_TAGS                                       \
    NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -108,8 +98,7 @@
            NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS,              \
            NLOHMANN_JSON_ABI_TAG_BRACE_INIT_COPY_SEMANTICS,         \
            NLOHMANN_JSON_ABI_TAG_PRECISE_STREAM_POSITION,           \
-            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING,               \
-            NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS)
+            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING)

 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
@@ -550,40 +550,11 @@ auto from_json(BasicJsonType&& j, TupleRelated&& t)
    return from_json_tuple_impl(std::forward<BasicJsonType>(j), std::forward<TupleRelated>(t), priority_tag<3> {});
 }

-// read a map with enum keys from an object, using the enum's own from_json for
-// the keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); this is the form written
-// with JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-template<typename BasicJsonType, typename Map>
-inline bool from_json_enum_keyed_object(const BasicJsonType& j, Map& m, std::true_type /*key is enum*/)
-{
-    if (!j.is_object())
-    {
-        return false;
-    }
-    m.clear();
-    for (const auto& p : *j.template get_ptr<const typename BasicJsonType::object_t*>())
-    {
-        m.emplace(BasicJsonType(p.first).template get<typename Map::key_type>(), p.second.template get<typename Map::mapped_type>());
-    }
-    return true;
-}
-
-template<typename BasicJsonType, typename Map>
-inline bool from_json_enum_keyed_object(const BasicJsonType& /*j*/, Map& /*m*/, std::false_type /*key is enum*/)
-{
-    return false;
-}
-
 template < typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
           typename = enable_if_t < !std::is_constructible <
                                        typename BasicJsonType::string_t, Key >::value >>
 inline void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allocator>& m)
 {
-    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
-    if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
-    {
-        return;
-    }
    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
    {
        JSON_THROW(type_error::create(302, concat("type must be array, but is ", j.type_name()), &j));
@@ -604,11 +575,6 @@ template < typename BasicJsonType, typename Key, typename Value, typename Hash,
                                        typename BasicJsonType::string_t, Key >::value >>
 inline void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyEqual, Allocator>& m)
 {
-    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
-    if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
-    {
-        return;
-    }
    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
    {
        JSON_THROW(type_error::create(302, concat("type must be array, but is ", j.type_name()), &j));
@@ -23,7 +23,6 @@
 #include <valarray> // valarray
 #include <vector> // vector

-#include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
 #include <nlohmann/detail/meta/std_fs.hpp>
@@ -382,9 +381,6 @@ template < typename BasicJsonType, typename CompatibleArrayType,
                         !is_basic_json<CompatibleArrayType>::value
 #if JSON_HAS_RANGES && !defined(__MINGW32__)
    && !is_compatible_range_view<CompatibleArrayType>::value
-#endif
-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    && !is_enum_keyed_map<CompatibleArrayType>::value
 #endif
                         ,
                         int > = 0 >
@@ -439,33 +435,6 @@ inline void to_json(BasicJsonType& j, const CompatibleObjectType& obj)
    external_constructor<value_t::object>::construct(j, obj);
 }

-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-// store a map with enum keys as an object, using the enum's own to_json for the
-// keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); without the macro, such maps
-// are stored as arrays of [key, value] pairs
-template < typename BasicJsonType, typename EnumKeyedMap,
-           enable_if_t < is_enum_keyed_map<EnumKeyedMap>::value&& !is_basic_json<EnumKeyedMap>::value, int > = 0 >
-inline void to_json(BasicJsonType& j, const EnumKeyedMap& map)
-{
-    typename BasicJsonType::object_t obj;
-    for (const auto& p : map)
-    {
-        BasicJsonType key = p.first;
-        if (JSON_HEDLEY_UNLIKELY(!key.is_string()))
-        {
-            JSON_THROW(type_error::create(302, concat("type must be string, but is ", key.type_name()), &key));
-        }
-
-        auto& key_string = *key.template get_ptr<typename BasicJsonType::string_t*>();
-        if (JSON_HEDLEY_UNLIKELY(!obj.emplace(key_string, BasicJsonType(p.second)).second))
-        {
-            JSON_THROW(type_error::create(318, concat("duplicate object key '", key_string, "'"), &key));
-        }
-    }
-    external_constructor<value_t::object>::construct(j, std::move(obj));
-}
-#endif
-
 template<typename BasicJsonType>
 inline void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
 {
@@ -915,7 +915,3 @@ void templated_json_throw(ExceptionType exception)
 #ifndef JSON_DISABLE_ENUM_SERIALIZATION
    #define JSON_DISABLE_ENUM_SERIALIZATION 0
 #endif
-
-#ifndef JSON_USE_GLOBAL_UDLS
-    #define JSON_USE_GLOBAL_UDLS 1
-#endif
@@ -25,7 +25,6 @@
 #undef JSON_INLINE_VARIABLE
 #undef JSON_NO_UNIQUE_ADDRESS
 #undef JSON_DISABLE_ENUM_SERIALIZATION
-#undef JSON_USE_GLOBAL_UDLS

 #ifndef JSON_TEST_KEEP_MACROS
    #undef JSON_CATCH
@@ -46,7 +45,6 @@
    #undef JSON_BRACE_INIT_COPY_SEMANTICS
    #undef JSON_PRECISE_STREAM_POSITION
    #undef JSON_STRICT_NUL_HANDLING
-    #undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
 #endif

 #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
@@ -400,30 +400,6 @@ template<typename BasicJsonType, typename CompatibleObjectType>
 struct is_compatible_object_type
    : is_compatible_object_type_impl<BasicJsonType, CompatibleObjectType> {};

-template<typename T>
-using insert_result_t = decltype(std::declval<T&>().insert(std::declval<const value_type_t<T>&>()));
-
-template<typename T>
-using insert_result_second_t = decltype(std::declval<T&>().insert(std::declval<const value_type_t<T>&>()).second);
-
-// a map-like type (std::map, std::unordered_map, ...) whose keys are enums; see
-// JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-template<typename T, typename = void>
-struct is_enum_keyed_map : std::false_type {};
-
-template<typename T>
-struct is_enum_keyed_map <
-    T, enable_if_t < is_detected<mapped_type_t, T>::value&&
-    is_detected<key_type_t, T>::value >>
-{
-    // maps with non-unique keys (std::multimap, std::unordered_multimap, ...)
-    // are excluded, because an object cannot hold duplicate keys; they are
-    // detected by insert() returning an iterator instead of a pair<iterator, bool>
-    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
-    static constexpr bool value = std::is_enum<typename T::key_type>::value &&
-                                  !(is_detected<insert_result_t, T>::value && !is_detected<insert_result_second_t, T>::value);
-};
-
 template<typename BasicJsonType, typename ConstructibleObjectType,
         typename = void>
 struct is_constructible_object_type_impl : std::false_type {};
@@ -6423,55 +6423,6 @@ std::string format_as(const NLOHMANN_BASIC_JSON_TPL& j)
    return j.dump();
 }

-inline namespace literals
-{
-inline namespace json_literals
-{
-
-/// @brief user-defined string literal for JSON values
-/// @sa https://json.nlohmann.me/api/basic_json/operator_literal_json/
-JSON_HEDLEY_NON_NULL(1)
-#if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
-    inline nlohmann::json operator""_json(const char* s, std::size_t n)
-#else
-    // GCC 4.8 requires a space between "" and suffix
-    inline nlohmann::json operator"" _json(const char* s, std::size_t n)
-#endif
-{
-    return nlohmann::json::parse(s, s + n);
-}
-
-#if defined(__cpp_char8_t)
-JSON_HEDLEY_NON_NULL(1)
-inline nlohmann::json operator""_json(const char8_t* s, std::size_t n)
-{
-    return nlohmann::json::parse(reinterpret_cast<const char*>(s),
-                                 reinterpret_cast<const char*>(s) + n);
-}
-#endif
-
-/// @brief user-defined string literal for JSON pointer
-/// @sa https://json.nlohmann.me/api/basic_json/operator_literal_json_pointer/
-JSON_HEDLEY_NON_NULL(1)
-#if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
-    inline nlohmann::json::json_pointer operator""_json_pointer(const char* s, std::size_t n)
-#else
-    // GCC 4.8 requires a space between "" and suffix
-    inline nlohmann::json::json_pointer operator"" _json_pointer(const char* s, std::size_t n)
-#endif
-{
-    return nlohmann::json::json_pointer(std::string(s, n));
-}
-
-#if defined(__cpp_char8_t)
-inline nlohmann::json::json_pointer operator""_json_pointer(const char8_t* s, std::size_t n)
-{
-    return nlohmann::json::json_pointer(std::string(reinterpret_cast<const char*>(s), n));
-}
-#endif
-
-}  // namespace json_literals
-}  // namespace literals
 NLOHMANN_JSON_NAMESPACE_END

 ///////////////////////
@@ -6606,17 +6557,6 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c

 }  // namespace std

-#if JSON_USE_GLOBAL_UDLS
-    #if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
-        using nlohmann::literals::json_literals::operator""_json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-        using nlohmann::literals::json_literals::operator""_json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-    #else
-        // GCC 4.8 requires a space between "" and suffix
-        using nlohmann::literals::json_literals::operator"" _json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-        using nlohmann::literals::json_literals::operator"" _json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-    #endif
-#endif
-
 #include <nlohmann/detail/macro_unscope.hpp>

 // End of GCC diagnostic pragmas for C++ modules support
@@ -6624,4 +6564,13 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
    #pragma GCC diagnostic pop
 #endif

+// The user-defined string literals are in a separate header, because their
+// bodies instantiate the parser in every translation unit that includes them.
+// Define JSON_NO_AUTOMATIC_UDLS to include <nlohmann/json_literals.hpp> only
+// where needed.
+#ifndef JSON_NO_AUTOMATIC_UDLS
+    // NOLINTNEXTLINE(misc-header-include-cycle): json_literals.hpp includes this header
+    #include <nlohmann/json_literals.hpp>
+#endif
+
 #endif  // INCLUDE_NLOHMANN_JSON_HPP_
@@ -0,0 +1,84 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#ifndef INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
+#define INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
+
+#include <cstddef> // size_t
+#include <string> // string
+
+// NOLINTNEXTLINE(misc-header-include-cycle): json.hpp includes this header at its end
+#include <nlohmann/json.hpp>
+
+// This header is included at the end of <nlohmann/json.hpp> unless
+// JSON_NO_AUTOMATIC_UDLS is defined, and can be included on its own after that.
+// Either way, the library's internal macros are no longer defined here (and the
+// amalgamation inlines macro_scope.hpp only once), so only standard and public
+// macros may be used below.
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+inline namespace literals
+{
+inline namespace json_literals
+{
+
+/// @brief user-defined string literal for JSON values
+/// @sa https://json.nlohmann.me/api/operator_literal_json/
+#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+    inline nlohmann::json operator""_json(const char* s, std::size_t n)
+#else
+    // GCC 4.8 requires a space between "" and suffix
+    inline nlohmann::json operator"" _json(const char* s, std::size_t n)
+#endif
+{
+    return nlohmann::json::parse(s, s + n);
+}
+
+#if defined(__cpp_char8_t)
+inline nlohmann::json operator""_json(const char8_t* s, std::size_t n)
+{
+    return nlohmann::json::parse(reinterpret_cast<const char*>(s),
+                                 reinterpret_cast<const char*>(s) + n);
+}
+#endif
+
+/// @brief user-defined string literal for JSON pointer
+/// @sa https://json.nlohmann.me/api/operator_literal_json_pointer/
+#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+    inline nlohmann::json::json_pointer operator""_json_pointer(const char* s, std::size_t n)
+#else
+    // GCC 4.8 requires a space between "" and suffix
+    inline nlohmann::json::json_pointer operator"" _json_pointer(const char* s, std::size_t n)
+#endif
+{
+    return nlohmann::json::json_pointer(std::string(s, n));
+}
+
+#if defined(__cpp_char8_t)
+inline nlohmann::json::json_pointer operator""_json_pointer(const char8_t* s, std::size_t n)
+{
+    return nlohmann::json::json_pointer(std::string(reinterpret_cast<const char*>(s), n));
+}
+#endif
+
+}  // namespace json_literals
+}  // namespace literals
+NLOHMANN_JSON_NAMESPACE_END
+
+#if !defined(JSON_USE_GLOBAL_UDLS) || JSON_USE_GLOBAL_UDLS
+    #if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+        using nlohmann::literals::json_literals::operator""_json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+        using nlohmann::literals::json_literals::operator""_json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+    #else
+        // GCC 4.8 requires a space between "" and suffix
+        using nlohmann::literals::json_literals::operator"" _json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+        using nlohmann::literals::json_literals::operator"" _json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+    #endif
+#endif
+
+#endif  // INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
@@ -15,6 +15,7 @@ nlohmann_json_multiple_headers = declare_dependency(
 if not meson.is_subproject()
 install_headers('single_include/nlohmann/json.hpp', subdir: 'nlohmann')
 install_headers('single_include/nlohmann/json_fwd.hpp', subdir: 'nlohmann')
+install_headers('single_include/nlohmann/json_literals.hpp', subdir: 'nlohmann')

 pkgc = import('pkgconfig')
 pkgc.generate(name: 'nlohmann_json',
@@ -103,10 +103,6 @@
    #define JSON_STRICT_NUL_HANDLING 0
 #endif

-#ifndef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
-#endif
-
 #if JSON_DIAGNOSTICS
    #define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
 #else
@@ -143,20 +139,14 @@
    #define NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING
 #endif

-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS _ekmo
-#else
-    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS
-#endif
-
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
    #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif

 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g) json_abi ## a ## b ## c ## d ## e ## f ## g
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g)
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f) json_abi ## a ## b ## c ## d ## e ## f
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f) \
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f)

 #define NLOHMANN_JSON_ABI_TAGS                                       \
    NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -165,8 +155,7 @@
            NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS,              \
            NLOHMANN_JSON_ABI_TAG_BRACE_INIT_COPY_SEMANTICS,         \
            NLOHMANN_JSON_ABI_TAG_PRECISE_STREAM_POSITION,           \
-            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING,               \
-            NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS)
+            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING)

 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
@@ -3338,10 +3327,6 @@ void templated_json_throw(ExceptionType exception)
    #define JSON_DISABLE_ENUM_SERIALIZATION 0
 #endif

-#ifndef JSON_USE_GLOBAL_UDLS
-    #define JSON_USE_GLOBAL_UDLS 1
-#endif
-
 #if JSON_HAS_THREE_WAY_COMPARISON
    #include <compare> // partial_ordering
 #endif
@@ -4421,30 +4406,6 @@ template<typename BasicJsonType, typename CompatibleObjectType>
 struct is_compatible_object_type
    : is_compatible_object_type_impl<BasicJsonType, CompatibleObjectType> {};

-template<typename T>
-using insert_result_t = decltype(std::declval<T&>().insert(std::declval<const value_type_t<T>&>()));
-
-template<typename T>
-using insert_result_second_t = decltype(std::declval<T&>().insert(std::declval<const value_type_t<T>&>()).second);
-
-// a map-like type (std::map, std::unordered_map, ...) whose keys are enums; see
-// JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-template<typename T, typename = void>
-struct is_enum_keyed_map : std::false_type {};
-
-template<typename T>
-struct is_enum_keyed_map <
-    T, enable_if_t < is_detected<mapped_type_t, T>::value&&
-    is_detected<key_type_t, T>::value >>
-{
-    // maps with non-unique keys (std::multimap, std::unordered_multimap, ...)
-    // are excluded, because an object cannot hold duplicate keys; they are
-    // detected by insert() returning an iterator instead of a pair<iterator, bool>
-    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
-    static constexpr bool value = std::is_enum<typename T::key_type>::value &&
-                                  !(is_detected<insert_result_t, T>::value && !is_detected<insert_result_second_t, T>::value);
-};
-
 template<typename BasicJsonType, typename ConstructibleObjectType,
         typename = void>
 struct is_constructible_object_type_impl : std::false_type {};
@@ -6082,40 +6043,11 @@ auto from_json(BasicJsonType&& j, TupleRelated&& t)
    return from_json_tuple_impl(std::forward<BasicJsonType>(j), std::forward<TupleRelated>(t), priority_tag<3> {});
 }

-// read a map with enum keys from an object, using the enum's own from_json for
-// the keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); this is the form written
-// with JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-template<typename BasicJsonType, typename Map>
-inline bool from_json_enum_keyed_object(const BasicJsonType& j, Map& m, std::true_type /*key is enum*/)
-{
-    if (!j.is_object())
-    {
-        return false;
-    }
-    m.clear();
-    for (const auto& p : *j.template get_ptr<const typename BasicJsonType::object_t*>())
-    {
-        m.emplace(BasicJsonType(p.first).template get<typename Map::key_type>(), p.second.template get<typename Map::mapped_type>());
-    }
-    return true;
-}
-
-template<typename BasicJsonType, typename Map>
-inline bool from_json_enum_keyed_object(const BasicJsonType& /*j*/, Map& /*m*/, std::false_type /*key is enum*/)
-{
-    return false;
-}
-
 template < typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
           typename = enable_if_t < !std::is_constructible <
                                        typename BasicJsonType::string_t, Key >::value >>
 inline void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allocator>& m)
 {
-    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
-    if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
-    {
-        return;
-    }
    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
    {
        JSON_THROW(type_error::create(302, concat("type must be array, but is ", j.type_name()), &j));
@@ -6136,11 +6068,6 @@ template < typename BasicJsonType, typename Key, typename Value, typename Hash,
                                        typename BasicJsonType::string_t, Key >::value >>
 inline void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyEqual, Allocator>& m)
 {
-    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
-    if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
-    {
-        return;
-    }
    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
    {
        JSON_THROW(type_error::create(302, concat("type must be array, but is ", j.type_name()), &j));
@@ -6236,8 +6163,6 @@ NLOHMANN_JSON_NAMESPACE_END
 #include <valarray> // valarray
 #include <vector> // vector

-// #include <nlohmann/detail/exceptions.hpp>
-
 // #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 //     __ _____ _____ _____
 //  __|  |   __|     |   | |  JSON for Modern C++
@@ -6981,9 +6906,6 @@ template < typename BasicJsonType, typename CompatibleArrayType,
                         !is_basic_json<CompatibleArrayType>::value
 #if JSON_HAS_RANGES && !defined(__MINGW32__)
    && !is_compatible_range_view<CompatibleArrayType>::value
-#endif
-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    && !is_enum_keyed_map<CompatibleArrayType>::value
 #endif
                         ,
                         int > = 0 >
@@ -7038,33 +6960,6 @@ inline void to_json(BasicJsonType& j, const CompatibleObjectType& obj)
    external_constructor<value_t::object>::construct(j, obj);
 }

-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-// store a map with enum keys as an object, using the enum's own to_json for the
-// keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); without the macro, such maps
-// are stored as arrays of [key, value] pairs
-template < typename BasicJsonType, typename EnumKeyedMap,
-           enable_if_t < is_enum_keyed_map<EnumKeyedMap>::value&& !is_basic_json<EnumKeyedMap>::value, int > = 0 >
-inline void to_json(BasicJsonType& j, const EnumKeyedMap& map)
-{
-    typename BasicJsonType::object_t obj;
-    for (const auto& p : map)
-    {
-        BasicJsonType key = p.first;
-        if (JSON_HEDLEY_UNLIKELY(!key.is_string()))
-        {
-            JSON_THROW(type_error::create(302, concat("type must be string, but is ", key.type_name()), &key));
-        }
-
-        auto& key_string = *key.template get_ptr<typename BasicJsonType::string_t*>();
-        if (JSON_HEDLEY_UNLIKELY(!obj.emplace(key_string, BasicJsonType(p.second)).second))
-        {
-            JSON_THROW(type_error::create(318, concat("duplicate object key '", key_string, "'"), &key));
-        }
-    }
-    external_constructor<value_t::object>::construct(j, std::move(obj));
-}
-#endif
-
 template<typename BasicJsonType>
 inline void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
 {
@@ -32605,55 +32500,6 @@ std::string format_as(const NLOHMANN_BASIC_JSON_TPL& j)
    return j.dump();
 }

-inline namespace literals
-{
-inline namespace json_literals
-{
-
-/// @brief user-defined string literal for JSON values
-/// @sa https://json.nlohmann.me/api/basic_json/operator_literal_json/
-JSON_HEDLEY_NON_NULL(1)
-#if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
-    inline nlohmann::json operator""_json(const char* s, std::size_t n)
-#else
-    // GCC 4.8 requires a space between "" and suffix
-    inline nlohmann::json operator"" _json(const char* s, std::size_t n)
-#endif
-{
-    return nlohmann::json::parse(s, s + n);
-}
-
-#if defined(__cpp_char8_t)
-JSON_HEDLEY_NON_NULL(1)
-inline nlohmann::json operator""_json(const char8_t* s, std::size_t n)
-{
-    return nlohmann::json::parse(reinterpret_cast<const char*>(s),
-                                 reinterpret_cast<const char*>(s) + n);
-}
-#endif
-
-/// @brief user-defined string literal for JSON pointer
-/// @sa https://json.nlohmann.me/api/basic_json/operator_literal_json_pointer/
-JSON_HEDLEY_NON_NULL(1)
-#if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
-    inline nlohmann::json::json_pointer operator""_json_pointer(const char* s, std::size_t n)
-#else
-    // GCC 4.8 requires a space between "" and suffix
-    inline nlohmann::json::json_pointer operator"" _json_pointer(const char* s, std::size_t n)
-#endif
-{
-    return nlohmann::json::json_pointer(std::string(s, n));
-}
-
-#if defined(__cpp_char8_t)
-inline nlohmann::json::json_pointer operator""_json_pointer(const char8_t* s, std::size_t n)
-{
-    return nlohmann::json::json_pointer(std::string(reinterpret_cast<const char*>(s), n));
-}
-#endif
-
-}  // namespace json_literals
-}  // namespace literals
 NLOHMANN_JSON_NAMESPACE_END

 ///////////////////////
@@ -32788,17 +32634,6 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c

 }  // namespace std

-#if JSON_USE_GLOBAL_UDLS
-    #if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
-        using nlohmann::literals::json_literals::operator""_json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-        using nlohmann::literals::json_literals::operator""_json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-    #else
-        // GCC 4.8 requires a space between "" and suffix
-        using nlohmann::literals::json_literals::operator"" _json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-        using nlohmann::literals::json_literals::operator"" _json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
-    #endif
-#endif
-
 // #include <nlohmann/detail/macro_unscope.hpp>
 //     __ _____ _____ _____
 //  __|  |   __|     |   | |  JSON for Modern C++
@@ -32827,7 +32662,6 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
 #undef JSON_INLINE_VARIABLE
 #undef JSON_NO_UNIQUE_ADDRESS
 #undef JSON_DISABLE_ENUM_SERIALIZATION
-#undef JSON_USE_GLOBAL_UDLS

 #ifndef JSON_TEST_KEEP_MACROS
    #undef JSON_CATCH
@@ -32848,7 +32682,6 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
    #undef JSON_BRACE_INIT_COPY_SEMANTICS
    #undef JSON_PRECISE_STREAM_POSITION
    #undef JSON_STRICT_NUL_HANDLING
-    #undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
 #endif

 // #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
@@ -33021,4 +32854,99 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
    #pragma GCC diagnostic pop
 #endif

+// The user-defined string literals are in a separate header, because their
+// bodies instantiate the parser in every translation unit that includes them.
+// Define JSON_NO_AUTOMATIC_UDLS to include <nlohmann/json_literals.hpp> only
+// where needed.
+#ifndef JSON_NO_AUTOMATIC_UDLS
+// NOLINTNEXTLINE(misc-header-include-cycle): json_literals.hpp includes this header
+// #include <nlohmann/json_literals.hpp>
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#ifndef INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
+#define INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
+
+#include <cstddef> // size_t
+#include <string> // string
+
+// NOLINTNEXTLINE(misc-header-include-cycle): json.hpp includes this header at its end
+// #include <nlohmann/json.hpp>
+
+
+// This header is included at the end of <nlohmann/json.hpp> unless
+// JSON_NO_AUTOMATIC_UDLS is defined, and can be included on its own after that.
+// Either way, the library's internal macros are no longer defined here (and the
+// amalgamation inlines macro_scope.hpp only once), so only standard and public
+// macros may be used below.
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+inline namespace literals
+{
+inline namespace json_literals
+{
+
+/// @brief user-defined string literal for JSON values
+/// @sa https://json.nlohmann.me/api/operator_literal_json/
+#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+    inline nlohmann::json operator""_json(const char* s, std::size_t n)
+#else
+    // GCC 4.8 requires a space between "" and suffix
+    inline nlohmann::json operator"" _json(const char* s, std::size_t n)
+#endif
+{
+    return nlohmann::json::parse(s, s + n);
+}
+
+#if defined(__cpp_char8_t)
+inline nlohmann::json operator""_json(const char8_t* s, std::size_t n)
+{
+    return nlohmann::json::parse(reinterpret_cast<const char*>(s),
+                                 reinterpret_cast<const char*>(s) + n);
+}
+#endif
+
+/// @brief user-defined string literal for JSON pointer
+/// @sa https://json.nlohmann.me/api/operator_literal_json_pointer/
+#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+    inline nlohmann::json::json_pointer operator""_json_pointer(const char* s, std::size_t n)
+#else
+    // GCC 4.8 requires a space between "" and suffix
+    inline nlohmann::json::json_pointer operator"" _json_pointer(const char* s, std::size_t n)
+#endif
+{
+    return nlohmann::json::json_pointer(std::string(s, n));
+}
+
+#if defined(__cpp_char8_t)
+inline nlohmann::json::json_pointer operator""_json_pointer(const char8_t* s, std::size_t n)
+{
+    return nlohmann::json::json_pointer(std::string(reinterpret_cast<const char*>(s), n));
+}
+#endif
+
+}  // namespace json_literals
+}  // namespace literals
+NLOHMANN_JSON_NAMESPACE_END
+
+#if !defined(JSON_USE_GLOBAL_UDLS) || JSON_USE_GLOBAL_UDLS
+    #if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+        using nlohmann::literals::json_literals::operator""_json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+        using nlohmann::literals::json_literals::operator""_json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+    #else
+        // GCC 4.8 requires a space between "" and suffix
+        using nlohmann::literals::json_literals::operator"" _json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+        using nlohmann::literals::json_literals::operator"" _json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+    #endif
+#endif
+
+#endif  // INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
+
+#endif
+
 #endif  // INCLUDE_NLOHMANN_JSON_HPP_
@@ -64,10 +64,6 @@
    #define JSON_STRICT_NUL_HANDLING 0
 #endif

-#ifndef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
-#endif
-
 #if JSON_DIAGNOSTICS
    #define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
 #else
@@ -104,20 +100,14 @@
    #define NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING
 #endif

-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS _ekmo
-#else
-    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS
-#endif
-
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
    #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif

 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g) json_abi ## a ## b ## c ## d ## e ## f ## g
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g)
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f) json_abi ## a ## b ## c ## d ## e ## f
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f) \
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f)

 #define NLOHMANN_JSON_ABI_TAGS                                       \
    NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -126,8 +116,7 @@
            NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS,              \
            NLOHMANN_JSON_ABI_TAG_BRACE_INIT_COPY_SEMANTICS,         \
            NLOHMANN_JSON_ABI_TAG_PRECISE_STREAM_POSITION,           \
-            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING,               \
-            NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS)
+            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING)

 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
@@ -0,0 +1,84 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#ifndef INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
+#define INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
+
+#include <cstddef> // size_t
+#include <string> // string
+
+// NOLINTNEXTLINE(misc-header-include-cycle): json.hpp includes this header at its end
+#include <nlohmann/json.hpp>
+
+// This header is included at the end of <nlohmann/json.hpp> unless
+// JSON_NO_AUTOMATIC_UDLS is defined, and can be included on its own after that.
+// Either way, the library's internal macros are no longer defined here (and the
+// amalgamation inlines macro_scope.hpp only once), so only standard and public
+// macros may be used below.
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+inline namespace literals
+{
+inline namespace json_literals
+{
+
+/// @brief user-defined string literal for JSON values
+/// @sa https://json.nlohmann.me/api/operator_literal_json/
+#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+    inline nlohmann::json operator""_json(const char* s, std::size_t n)
+#else
+    // GCC 4.8 requires a space between "" and suffix
+    inline nlohmann::json operator"" _json(const char* s, std::size_t n)
+#endif
+{
+    return nlohmann::json::parse(s, s + n);
+}
+
+#if defined(__cpp_char8_t)
+inline nlohmann::json operator""_json(const char8_t* s, std::size_t n)
+{
+    return nlohmann::json::parse(reinterpret_cast<const char*>(s),
+                                 reinterpret_cast<const char*>(s) + n);
+}
+#endif
+
+/// @brief user-defined string literal for JSON pointer
+/// @sa https://json.nlohmann.me/api/operator_literal_json_pointer/
+#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+    inline nlohmann::json::json_pointer operator""_json_pointer(const char* s, std::size_t n)
+#else
+    // GCC 4.8 requires a space between "" and suffix
+    inline nlohmann::json::json_pointer operator"" _json_pointer(const char* s, std::size_t n)
+#endif
+{
+    return nlohmann::json::json_pointer(std::string(s, n));
+}
+
+#if defined(__cpp_char8_t)
+inline nlohmann::json::json_pointer operator""_json_pointer(const char8_t* s, std::size_t n)
+{
+    return nlohmann::json::json_pointer(std::string(reinterpret_cast<const char*>(s), n));
+}
+#endif
+
+}  // namespace json_literals
+}  // namespace literals
+NLOHMANN_JSON_NAMESPACE_END
+
+#if !defined(JSON_USE_GLOBAL_UDLS) || JSON_USE_GLOBAL_UDLS
+    #if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+        using nlohmann::literals::json_literals::operator""_json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+        using nlohmann::literals::json_literals::operator""_json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+    #else
+        // GCC 4.8 requires a space between "" and suffix
+        using nlohmann::literals::json_literals::operator"" _json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+        using nlohmann::literals::json_literals::operator"" _json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
+    #endif
+#endif
+
+#endif  // INCLUDE_NLOHMANN_JSON_LITERALS_HPP_
@@ -18,6 +18,7 @@ module;
 // See: https://github.com/nlohmann/json/issues/5103

 #include <nlohmann/json.hpp>
+#include <nlohmann/json_literals.hpp>

 export module nlohmann.json;

@@ -44,10 +44,6 @@ TEST_CASE("default namespace")
        expected += "_snul";
 #endif

-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-        expected += "_ekmo";
-#endif
-
        expected += "_v" STRINGIZE(NLOHMANN_JSON_VERSION_MAJOR);
        expected += "_" STRINGIZE(NLOHMANN_JSON_VERSION_MINOR);
        expected += "_" STRINGIZE(NLOHMANN_JSON_VERSION_PATCH) "::basic_json";
@@ -45,10 +45,6 @@ TEST_CASE("default namespace without version component")
        expected += "_snul";
 #endif

-#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-        expected += "_ekmo";
-#endif
-
        expected += "::basic_json";

        // fallback for Clang
@@ -1,246 +0,0 @@
-//     __ _____ _____ _____
-//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
-// |  |  |__   |  |  | | | |  version 3.12.0
-// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
-//
-// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
-// SPDX-License-Identifier: MIT
-
-#include "doctest_compatibility.h"
-
-// skip tests if JSON_DisableEnumSerialization=ON (#4384)
-#if defined(JSON_DISABLE_ENUM_SERIALIZATION) && (JSON_DISABLE_ENUM_SERIALIZATION == 1)
-    #define SKIP_TESTS_FOR_ENUM_SERIALIZATION
-#endif
-
-// This file tests the opt-in JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS, so it defines
-// the macro itself rather than relying on a -D flag, and runs in every build.
-// The default behavior is tested in unit-enum_keyed_maps_default.cpp.
-#ifdef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    #undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-#endif
-
-#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 1
-
-#include <nlohmann/json.hpp>
-using nlohmann::json;
-using nlohmann::ordered_json;
-
-#include <cstddef>
-#include <functional>
-#include <map>
-#include <string>
-#include <unordered_map>
-#include <utility>
-#include <vector>
-
-#define STRINGIZE_EX(x) #x
-#define STRINGIZE(x) STRINGIZE_EX(x)
-
-// NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
-DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
-DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
-
-namespace
-{
-// std::hash is only required for enums since C++14
-struct enum_hash
-{
-    template<typename T>
-    std::size_t operator()(T t) const noexcept
-    {
-        return static_cast<std::size_t>(t);
-    }
-};
-} // namespace
-
-// the example from #4378
-enum TaskState // NOLINT(cert-int09-c,readability-enum-initial-value,cppcoreguidelines-use-enum-class)
-{
-    TS_STOPPED,
-    TS_RUNNING,
-    TS_COMPLETED,
-    TS_INVALID = -1,
-};
-
-// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
-NLOHMANN_JSON_SERIALIZE_ENUM(TaskState,
-{
-    {TS_INVALID, nullptr},
-    {TS_STOPPED, "stopped"},
-    {TS_RUNNING, "running"},
-    {TS_COMPLETED, "completed"},
-})
-
-enum class color {red, green, blue}; // blue is not mapped and falls back to "red"
-
-// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
-NLOHMANN_JSON_SERIALIZE_ENUM(color,
-{
-    {color::red, "red"},
-    {color::green, "green"},
-})
-
-enum class strict_color {red, green, blue}; // blue is not mapped
-
-// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
-NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(strict_color,
-{
-    {strict_color::red, "red"},
-    {strict_color::green, "green"},
-})
-
-enum class digit {zero, one};
-
-// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
-NLOHMANN_JSON_SERIALIZE_ENUM(digit,
-{
-    {digit::zero, 0},
-    {digit::one, 1},
-})
-
-#ifndef SKIP_TESTS_FOR_ENUM_SERIALIZATION
-enum class plain {zero, one}; // serialized as integer
-#endif
-
-TEST_CASE("JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS")
-{
-    SECTION("the macro is part of the ABI tag")
-    {
-        const std::string ns = STRINGIZE(NLOHMANN_JSON_NAMESPACE);
-        CHECK(ns.find("_ekmo") != std::string::npos);
-    }
-
-    SECTION("std::map (#4378)")
-    {
-        using task_map = std::map<TaskState, std::string>;
-        const task_map m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
-        const json j = m;
-        CHECK(j == json::parse(R"({"stopped":"aa","completed":"bb"})"));
-        CHECK(j.get<task_map>() == m);
-
-        json j2;
-        j2["x"] = m;
-        CHECK(j2.dump() == R"({"x":{"completed":"bb","stopped":"aa"}})");
-    }
-
-    SECTION("std::map with custom comparator")
-    {
-        using task_map = std::map<TaskState, int, std::greater<TaskState>>;
-        const task_map m = {{TS_STOPPED, 1}, {TS_RUNNING, 2}};
-        const json j = m;
-        CHECK(j == json::parse(R"({"stopped":1,"running":2})"));
-        CHECK(j.get<task_map>() == m);
-    }
-
-    SECTION("std::unordered_map")
-    {
-        using task_map = std::unordered_map<TaskState, int, enum_hash>;
-        const task_map m = {{TS_STOPPED, 1}, {TS_RUNNING, 2}};
-        const json j = m;
-        CHECK(j == json::parse(R"({"stopped":1,"running":2})"));
-        CHECK(j.get<task_map>() == m);
-    }
-
-    SECTION("nested maps")
-    {
-        using nested_map = std::map<color, std::map<TaskState, int>>;
-        const nested_map m = {{color::green, {{TS_RUNNING, 1}}}, {color::red, {}}};
-        const json j = m;
-        CHECK(j == json::parse(R"({"green":{"running":1},"red":{}})"));
-        CHECK(j.get<nested_map>() == m);
-    }
-
-    SECTION("ordered_json keeps the order of the map")
-    {
-        using task_map = std::map<TaskState, int>;
-        const task_map m = {{TS_STOPPED, 1}, {TS_RUNNING, 2}, {TS_COMPLETED, 3}};
-        const ordered_json j = m;
-        CHECK(j.dump() == R"({"stopped":1,"running":2,"completed":3})");
-        CHECK(j.get<task_map>() == m);
-    }
-
-    SECTION("empty map")
-    {
-        const json j = std::map<TaskState, int>();
-        CHECK(j.is_object());
-        CHECK(j.empty());
-    }
-
-    SECTION("NLOHMANN_JSON_SERIALIZE_ENUM_STRICT")
-    {
-        using color_map = std::map<strict_color, int>;
-        const color_map m = {{strict_color::red, 1}, {strict_color::green, 2}};
-        const json j = m;
-        CHECK(j == json::parse(R"({"red":1,"green":2})"));
-        CHECK(j.get<color_map>() == m);
-
-        const color_map unmapped = {{strict_color::blue, 1}};
-        json _;
-        CHECK_THROWS_WITH_AS(_ = unmapped,
-                             "[json.exception.out_of_range.410] enum value out of range for strict_color", json::out_of_range&);
-    }
-
-    SECTION("arrays of [key, value] pairs are still read")
-    {
-        using task_map = std::map<TaskState, int>;
-        const task_map m = {{TS_STOPPED, 1}};
-        CHECK(json::parse(R"([["stopped",1]])").get<task_map>() == m);
-    }
-
-    SECTION("other containers are not affected")
-    {
-        const std::vector<std::pair<TaskState, int>> pairs = {{TS_STOPPED, 1}};
-        const std::map<std::string, TaskState> string_keys = {{"a", TS_STOPPED}};
-        const std::map<int, int> int_keys = {{1, 2}};
-        CHECK(json(pairs) == json::parse(R"([["stopped",1]])"));
-        CHECK(json(string_keys) == json::parse(R"({"a":"stopped"})"));
-        CHECK(json(int_keys) == json::parse("[[1,2]]"));
-    }
-
-    SECTION("maps with non-unique keys are still stored as arrays of pairs")
-    {
-        const std::multimap<TaskState, int> mm = {{TS_STOPPED, 1}, {TS_STOPPED, 2}};
-        const std::unordered_multimap<TaskState, int, enum_hash> umm = {{TS_RUNNING, 3}, {TS_RUNNING, 3}};
-        CHECK(json(mm) == json::parse(R"([["stopped",1],["stopped",2]])"));
-        CHECK(json(umm) == json::parse(R"([["running",3],["running",3]])"));
-    }
-
-    SECTION("keys that do not serialize to strings")
-    {
-        const std::map<TaskState, int> null_key = {{TS_INVALID, 1}};
-        const std::map<digit, int> number_key = {{digit::zero, 1}};
-        json j = "unchanged";
-
-        // mapped to null
-        CHECK_THROWS_WITH_AS(j = null_key,
-                             "[json.exception.type_error.302] type must be string, but is null", json::type_error&);
-
-        // mapped to a number
-        CHECK_THROWS_WITH_AS(j = number_key,
-                             "[json.exception.type_error.302] type must be string, but is number", json::type_error&);
-
-#ifndef SKIP_TESTS_FOR_ENUM_SERIALIZATION
-        // enum without NLOHMANN_JSON_SERIALIZE_ENUM
-        const std::map<plain, int> plain_key = {{plain::zero, 1}};
-        CHECK_THROWS_WITH_AS(j = plain_key,
-                             "[json.exception.type_error.302] type must be string, but is number", json::type_error&);
-#endif
-
-        CHECK(j == "unchanged");
-    }
-
-    SECTION("keys that serialize to the same string")
-    {
-        const std::map<color, int> m = {{color::red, 1}, {color::blue, 2}};
-        json j = "unchanged";
-
-        // color::blue is not mapped and falls back to "red"
-        CHECK_THROWS_WITH_AS(j = m,
-                             "[json.exception.type_error.318] duplicate object key 'red'", json::type_error&);
-
-        CHECK(j == "unchanged");
-    }
-}
-
-DOCTEST_CLANG_SUPPRESS_WARNING_POP
@@ -1,144 +0,0 @@
-//     __ _____ _____ _____
-//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
-// |  |  |__   |  |  | | | |  version 3.12.0
-// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
-//
-// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
-// SPDX-License-Identifier: MIT
-
-#include "doctest_compatibility.h"
-
-// This file tests maps with enum keys with the default setting of
-// JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS (or whatever a -D flag sets it to).
-// unit-enum_keyed_maps.cpp tests JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS=1.
-// These tests are not part of unit-conversions.cpp, because that object file
-// is already too big for the MinGW linker of some compilers.
-
-#include <nlohmann/json.hpp>
-using nlohmann::json;
-
-#include <cstddef>
-#include <functional>
-#include <map>
-#include <string>
-#include <unordered_map>
-
-// NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
-DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
-DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
-
-enum class cards {kreuz, pik, herz, karo};
-
-// NOLINTNEXTLINE(misc-use-internal-linkage,misc-const-correctness,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
-NLOHMANN_JSON_SERIALIZE_ENUM(cards,
-{
-    {cards::kreuz, "kreuz"},
-    {cards::pik, "pik"},
-    {cards::herz, "herz"},
-    {cards::karo, "karo"}
-})
-
-enum TaskState // NOLINT(cert-int09-c,readability-enum-initial-value,cppcoreguidelines-use-enum-class)
-{
-    TS_STOPPED,
-    TS_RUNNING,
-    TS_COMPLETED,
-    TS_INVALID = -1,
-};
-
-// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
-NLOHMANN_JSON_SERIALIZE_ENUM(TaskState,
-{
-    {TS_INVALID, nullptr},
-    {TS_STOPPED, "stopped"},
-    {TS_RUNNING, "running"},
-    {TS_COMPLETED, "completed"},
-})
-
-enum class strict_cards {kreuz, pik, herz, karo, andere}; // andere not included in mapping
-
-// NOLINTNEXTLINE(misc-use-internal-linkage,misc-const-correctness,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
-NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(strict_cards,
-{
-    {strict_cards::kreuz, "kreuz"},
-    {strict_cards::pik, "pik"},
-    {strict_cards::herz, "herz"},
-    {strict_cards::karo, "karo"}
-})
-
-namespace
-{
-// std::hash is only required for enums since C++14
-struct enum_hash
-{
-    template<typename T>
-    std::size_t operator()(T t) const noexcept
-    {
-        return static_cast<std::size_t>(t);
-    }
-};
-} // namespace
-
-// see unit-enum_keyed_maps.cpp for JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS=1
-TEST_CASE("maps with enum keys")
-{
-    using task_map = std::map<TaskState, std::string>;
-    using task_umap = std::unordered_map<TaskState, std::string, enum_hash>;
-    using task_gmap = std::map<TaskState, std::string, std::greater<TaskState>>;
-    using nested_map = std::map<cards, std::map<TaskState, int>>;
-    using strict_map = std::map<strict_cards, int>;
-    using int_map = std::map<int, int>;
-    using int_umap = std::unordered_map<int, int>;
-
-    const task_map m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
-
-#if !JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
-    SECTION("stored as array of pairs")
-    {
-        CHECK(json(m) == json::parse(R"([["stopped","aa"],["completed","bb"]])"));
-        CHECK(json(task_umap {{TS_RUNNING, "cc"}}) == json::parse(R"([["running","cc"]])"));
-    }
-#endif
-
-    SECTION("read from array of pairs")
-    {
-        CHECK(json::parse(R"([["stopped","aa"],["completed","bb"]])").get<task_map>() == m);
-    }
-
-    SECTION("read from object (#4378)")
-    {
-        const json j = json::parse(R"({"stopped":"aa","completed":"bb"})");
-        CHECK(j.get<task_map>() == m);
-        CHECK(j.get<task_umap>() == task_umap(m.begin(), m.end()));
-        CHECK(j.get<task_gmap>() == task_gmap(m.begin(), m.end()));
-        CHECK(json::parse(R"({"kreuz":{"stopped":1}})").get<nested_map>() == nested_map {{cards::kreuz, {{TS_STOPPED, 1}}}});
-        CHECK(nlohmann::ordered_json::parse(R"({"stopped":"aa","completed":"bb"})").get<task_map>() == m);
-
-        // object keys go through the enum's from_json
-        strict_map sm;
-        CHECK_THROWS_WITH_AS(json::parse(R"({"what?":1})").get_to(sm),
-                             "[json.exception.out_of_range.410] enum value out of range for strict_cards: \"what?\"", json::out_of_range&);
-    }
-
-    SECTION("objects are only read for enum keys")
-    {
-        // built rather than parsed, so that the messages do not gain a byte
-        // range with JSON_DIAGNOSTIC_POSITIONS
-        const json j = {{"1", 2}};
-        int_map im;
-        int_umap ium;
-        CHECK_THROWS_WITH_AS(j.get_to(im),
-                             "[json.exception.type_error.302] type must be array, but is object", json::type_error&);
-        CHECK_THROWS_WITH_AS(j.get_to(ium),
-                             "[json.exception.type_error.302] type must be array, but is object", json::type_error&);
-    }
-
-    SECTION("other types are rejected")
-    {
-        task_map tm;
-        CHECK_THROWS_WITH_AS(json("stopped").get_to(tm),
-                             "[json.exception.type_error.302] type must be array, but is string", json::type_error&);
-    }
-}
-
-DOCTEST_CLANG_SUPPRESS_WARNING_POP
@@ -0,0 +1,108 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+// This translation unit checks JSON_NO_AUTOMATIC_UDLS, which keeps
+// <nlohmann/json.hpp> from including <nlohmann/json_literals.hpp> and thereby
+// leaves out the user-defined string literals operator""_json and
+// operator""_json_pointer (see #5294), and that including
+// <nlohmann/json_literals.hpp> afterwards brings them back.
+#define JSON_NO_AUTOMATIC_UDLS 1
+
+#include "doctest_compatibility.h"
+
+#include <cstddef>
+#include <utility>
+
+#include <nlohmann/json.hpp>
+using json = nlohmann::json;
+
+// An argument type whose associated namespace is the library namespace, so
+// argument-dependent lookup of a literal operator called by its function name
+// also searches the inline namespaces nlohmann::literals::json_literals.
+NLOHMANN_JSON_NAMESPACE_BEGIN
+struct no_automatic_udls_probe
+{
+    operator const char* () const // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+    {
+        return "";
+    }
+};
+NLOHMANN_JSON_NAMESPACE_END
+
+namespace
+{
+// The calls below use a dependent argument, so a literal operator that is not
+// declared at all is a substitution failure rather than a hard error: lookup is
+// deferred to the point of instantiation, where it considers the declarations
+// visible from here (the global using-declarations of JSON_USE_GLOBAL_UDLS) plus
+// argument-dependent lookup (the literals in the library namespace).
+#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
+    template<typename T>
+    using json_udl_t = decltype(operator""_json(std::declval<T>(), std::size_t()));
+
+    template<typename T>
+    using json_pointer_udl_t = decltype(operator""_json_pointer(std::declval<T>(), std::size_t()));
+#else
+    // GCC 4.8 requires a space between "" and suffix
+    template<typename T>
+    using json_udl_t = decltype(operator"" _json(std::declval<T>(), std::size_t()));
+
+    template<typename T>
+    using json_pointer_udl_t = decltype(operator"" _json_pointer(std::declval<T>(), std::size_t()));
+#endif
+
+template<typename T>
+using has_json_udl = nlohmann::detail::is_detected<json_udl_t, T>;
+
+template<typename T>
+using has_json_pointer_udl = nlohmann::detail::is_detected<json_pointer_udl_t, T>;
+} // namespace
+
+TEST_CASE("JSON_NO_AUTOMATIC_UDLS")
+{
+    SECTION("literals are not declared")
+    {
+        // global namespace (JSON_USE_GLOBAL_UDLS defaults to 1)
+        CHECK_FALSE(has_json_udl<const char*>::value);
+        CHECK_FALSE(has_json_pointer_udl<const char*>::value);
+
+        // nlohmann::literals::json_literals
+        CHECK_FALSE(has_json_udl<nlohmann::no_automatic_udls_probe>::value);
+        CHECK_FALSE(has_json_pointer_udl<nlohmann::no_automatic_udls_probe>::value);
+    }
+
+    SECTION("the rest of the library keeps working")
+    {
+        const json j = json::parse(R"({"foo": {"bar": 42}})");
+        CHECK(j.dump() == R"({"foo":{"bar":42}})");
+
+        const json::json_pointer ptr("/foo/bar");
+        CHECK(j.at(ptr) == 42);
+        CHECK(j.contains(ptr));
+    }
+}
+
+// the literals can still be added where they are needed
+#include <nlohmann/json_literals.hpp>
+
+TEST_CASE("JSON_NO_AUTOMATIC_UDLS with <nlohmann/json_literals.hpp>")
+{
+#if !defined(JSON_USE_GLOBAL_UDLS) || JSON_USE_GLOBAL_UDLS
+    SECTION("global namespace")
+    {
+        CHECK("[1,2]"_json == json({1, 2}));
+        CHECK("/a/0"_json_pointer == json::json_pointer("/a/0"));
+    }
+#endif
+
+    SECTION("nlohmann::literals::json_literals")
+    {
+        using namespace nlohmann::literals::json_literals; // NOLINT(google-build-using-namespace)
+        CHECK(R"({"a":[42]})"_json.at("/a/0"_json_pointer) == 42);
+    }
+}
@@ -20,7 +20,7 @@ if __name__ == '__main__':

    namespaces = ['nlohmann']
    abi_prefix = 'json_abi'
-    abi_tags = ['_diag', '_ldvcmp', '_dp', '_bics', '_psp', '_snul', '_ekmo']
+    abi_tags = ['_diag', '_ldvcmp', '_dp', '_bics', '_psp', '_snul']
    version = '_v' + args.version.replace('.', '_')
    inline_namespaces = []
Author	SHA1	Message	Date
Niels Lohmann	d324da8632	Document options to reduce compile times Add an integration page that collects the ways to reduce compile times with measurements: json_fwd.hpp in headers, JSON_NO_AUTOMATIC_UDLS, explicit instantiation with extern template, modules, and precompiled headers, and notes that JSON_NO_IO and JSON_USE_GLOBAL_UDLS have no measurable effect. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-29 16:41:53 +02:00
Niels Lohmann	a00c951d52	Fix CI: include cycle, GCC 4.8 literal operator spacing, and global UDLs off in the JSON_NO_AUTOMATIC_UDLS test - Suppress clang-tidy misc-header-include-cycle on the intentional mutual include of json.hpp and json_literals.hpp. - Use operator"" _json with a space for GCC 4.8 in the test's detection aliases, as the header does. - Only test the global literal operators when JSON_USE_GLOBAL_UDLS is on. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-29 16:40:12 +02:00
Niels Lohmann	71b9c4a88d	Merge branch 'develop' into claude/json-no-udls-e999fc Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 22:22:15 +02:00
Niels Lohmann	1419aeff60	Move the user-defined string literals to <nlohmann/json_literals.hpp> Following the review in #5294, the literals now live in their own header instead of being removed entirely: <nlohmann/json.hpp> includes it at the end unless JSON_NO_AUTOMATIC_UDLS (renamed from JSON_NO_UDLS) is defined, so a project can opt out globally and include the header only where the literals are used. The header only uses public and standard macros, because the library's internal macros are undefined at the end of json.hpp and the amalgamation inlines macro_scope.hpp only once. For the same reason, the library no longer defines and undefines JSON_USE_GLOBAL_UDLS, so a user's definition is still visible to the header. The single-header copy is identical to the multi-header one, as it only includes <nlohmann/json.hpp>. The module always exports the literals. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 21:49:37 +02:00
Niels Lohmann	e0ee07fe73	Mention JSON_NO_UDLS in the list of exported module symbols Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 21:24:40 +02:00
Niels Lohmann	dc4a70e7b4	Add JSON_NO_UDLS to leave out the user-defined string literals The bodies of operator""_json and operator""_json_pointer call the parser, so every translation unit including the library instantiates it, even if it never parses anything. Defining JSON_NO_UDLS leaves the literals out entirely, which saves 15-35% compile time for such translation units (#5294). Nothing changes if the macro is not defined. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 21:23:52 +02:00