Merge branch 'develop' into claude/issue-3885-3dcafd

Conflicts:
- Makefile: include.zip lists both develop's $(AMALGAMATED_LITERALS_FILE)
  and this PR's meson_options.txt
- meson.build: kept this PR's install_subdir(incdir / 'nlohmann'), which
  already installs develop's new json_literals.hpp in both header modes,
  in place of develop's per-file install_headers() lines

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/workflows/ubuntu.yml

@@ -31,6 +31,45 @@ jobs:
       - name: Build
         run: cmake --build build --target ci_test_gcc
 
+  ci_meson_install:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+      - name: Install Meson
+        run: pip install meson
+      - name: Install with Meson
+        run: |
+          meson setup build-meson --prefix=${{ github.workspace }}/install
+          meson install -C build-meson
+      - name: Use the installed package with find_package
+        run: |
+          cmake -S tests/cmake_import/project -B build-import -DCMAKE_PREFIX_PATH=${{ github.workspace }}/install
+          cmake --build build-import
+      - name: Install with Meson and non-default options
+        run: |
+          meson setup build-meson-options --prefix=${{ github.workspace }}/install-options -DMultipleHeaders=true -DDiagnostics=true -DGlobalUDLs=false
+          meson install -C build-meson-options
+      - name: Check that the options reach the installed files
+        run: |
+          test -d install-options/include/nlohmann/detail
+          cflags=$(PKG_CONFIG_PATH=${{ github.workspace }}/install-options/share/pkgconfig pkg-config --cflags nlohmann_json)
+          echo "$cflags"
+          echo "$cflags" | grep -q -- '-DJSON_DIAGNOSTICS=1'
+          echo "$cflags" | grep -q -- '-DJSON_USE_GLOBAL_UDLS=0'
+          grep -q 'JSON_USE_GLOBAL_UDLS=0;JSON_DIAGNOSTICS=1' install-options/share/cmake/nlohmann_json/nlohmann_jsonTargets.cmake
+          cmake -S tests/cmake_import/project -B build-import-options -DCMAKE_PREFIX_PATH=${{ github.workspace }}/install-options
+          cmake --build build-import-options
+      - name: Install with Meson and the include directory outside the prefix
+        run: |
+          meson setup build-meson-split --prefix=${{ github.workspace }}/install-split --includedir=${{ github.workspace }}/install-split-dev/include
+          meson install -C build-meson-split
+          cmake -S tests/cmake_import/project -B build-import-split -DCMAKE_PREFIX_PATH=${{ github.workspace }}/install-split
+          cmake --build build-import-split
+
   ci_infer:
     runs-on: ubuntu-latest
     steps:

CMakeLists.txt

@@ -168,7 +168,30 @@ if (MSVC)
     )
 endif()
 
-# Install a pkg-config file, so other tools can find this.
+# Install a pkg-config file, so other tools can find this. It carries the same
+# compile definitions as the target above.
+set(NLOHMANN_JSON_PKGCONFIG_CFLAGS "")
+if (NOT JSON_GlobalUDLs)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_USE_GLOBAL_UDLS=0")
+endif()
+if (NOT JSON_ImplicitConversions)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_USE_IMPLICIT_CONVERSIONS=0")
+endif()
+if (JSON_DisableEnumSerialization)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_DISABLE_ENUM_SERIALIZATION=1")
+endif()
+if (JSON_Diagnostics)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_DIAGNOSTICS=1")
+endif()
+if (JSON_Diagnostic_Positions)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_DIAGNOSTIC_POSITIONS=1")
+endif()
+if (JSON_LegacyDiscardedValueComparison)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1")
+endif()
+if (JSON_StrictNulHandling)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_STRICT_NUL_HANDLING=1")
+endif()
 configure_file(
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake/pkg-config.pc.in"
     "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"

FILES.md

@@ -260,9 +260,29 @@ make BUILD.bazel
 
 The "Check amalgamation" workflow fails if the file is out of date.
 
-### `meson.build`
+### `meson.build` and `meson_options.txt`
 
-The build definition for the [Meson](https://mesonbuild.com) build system.
+Meson build definitions suitable for use as a subproject ("wrap" in Meson terminology).
+
+Projects wishing to use the wrap can execute:
+```sh
+meson wrap install nlohmann_json
+```
+
+Which allows Meson to build from source when a system provided dependency isn't available.
+
+To build directly:
+```sh
+meson setup builddir
+ninja -C builddir
+```
+
+`meson_options.txt` defines the options, which mirror the CMake options that change the library's target (for example,
+`-DDiagnostics=true`). Meson requires this file next to `meson.build`, so it is also part of `include.zip`.
+
+When installing, `meson.build` installs the headers, a pkg-config file, and the CMake package config files, so that
+`find_package(nlohmann_json)` works. As Meson cannot generate `nlohmann_jsonTargets.cmake` itself, it is created from
+the template `cmake/nlohmann_jsonTargets.cmake.in`, which is only used by Meson.
 
 ### `Package.swift`
 

Makefile

@@ -231,7 +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) $(AMALGAMATED_LITERALS_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 meson_options.txt LICENSE.MIT
 
 # Create the files for a release and add signatures and hashes.
 release: include.zip json.tar.xz

cmake/nlohmann_jsonTargets.cmake.in

@@ -0,0 +1,38 @@
+# Imported target for installations made with Meson (see meson.build).
+#
+# CMake installations generate this file with install(EXPORT ...). Meson cannot
+# do that, but as the library is header-only, the target only needs an include
+# directory, the C++ standard, and the compile definitions of the options that
+# differ from their defaults. Paths are computed relative to this file so that
+# the installation can be relocated (e.g., into a sysroot), unless includedir or
+# datadir is outside the prefix.
+
+if(TARGET @PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@)
+    return()
+endif()
+
+get_filename_component(_IMPORT_PREFIX "${CMAKE_CURRENT_LIST_DIR}/@NLOHMANN_JSON_CONFIG_TO_PREFIX@" ABSOLUTE)
+
+add_library(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ INTERFACE IMPORTED)
+set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES "@NLOHMANN_JSON_INCLUDE_DIR@"
+)
+if(CMAKE_VERSION VERSION_LESS 3.8)
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_FEATURES cxx_range_for
+    )
+else()
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_FEATURES cxx_std_11
+    )
+endif()
+
+set(_NLOHMANN_JSON_COMPILE_DEFINITIONS "@NLOHMANN_JSON_COMPILE_DEFINITIONS@")
+if(_NLOHMANN_JSON_COMPILE_DEFINITIONS)
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_DEFINITIONS "${_NLOHMANN_JSON_COMPILE_DEFINITIONS}"
+    )
+endif()
+
+unset(_NLOHMANN_JSON_COMPILE_DEFINITIONS)
+unset(_IMPORT_PREFIX)

cmake/pkg-config.pc.in

@@ -4,4 +4,4 @@ includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
 Name: @PROJECT_NAME@
 Description: JSON for Modern C++
 Version: @PROJECT_VERSION@
-Cflags: -I${includedir}
+Cflags: -I${includedir}@NLOHMANN_JSON_PKGCONFIG_CFLAGS@

docs/mkdocs/docs/api/macros/json_no_automatic_udls.md

@@ -62,7 +62,6 @@ By default, `#!cpp JSON_NO_AUTOMATIC_UDLS` is not defined, and `<nlohmann/json.h
 - [`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
 

docs/mkdocs/docs/api/operator_gtgt.md

@@ -18,6 +18,10 @@ Deserializes an input stream to a JSON value.
 
 the stream `i`
 
+## Exception safety
+
+Strong guarantee: if an exception is thrown, there are no changes in `j`.
+
 ## Exceptions
 
 - Throws [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token, or if
@@ -125,3 +129,5 @@ being read.
   the stream; planned to become the default in version 4.0.0.
 - Fixed a null pointer dereference for an `std::istream` without a stream buffer (now throws `parse_error.101`), and a
   crash (`std::terminate`) when `i` has `eofbit` in its exception mask, in version 3.13.0.
+- Changed to the strong exception safety guarantee in version 3.13.0: `j` is no longer left with a partially parsed
+  value if parsing throws.

docs/mkdocs/docs/features/types/template_parameters.md

@@ -389,6 +389,7 @@ using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;
 | Functionality                                                                                                                     | Additional requirement                                                                                                                                                                       |
 |-----------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | [`diff`](../../api/basic_json/diff.md), [`items`](../../api/basic_json/items.md), [`std::hash`](../../api/basic_json/std_hash.md) | conversion of a `#!cpp std::size_t` to `StringType`: either assignability from the result of `#!cpp std::to_string`, or an ADL overload `#!cpp void int_to_string(StringType&, std::size_t)` |
+| [`operator/(std::size_t)`](../../api/json_pointer/operator_slash.md)                                                              | the same conversion of a `#!cpp std::size_t` to `StringType` as `diff`, `items`, and `std::hash` above                                                                                       |
 | [`std::hash<basic_json>`](../../api/basic_json/std_hash.md)                                                                       | additionally a specialization of `#!cpp std::hash<StringType>`                                                                                                                               |
 | [`to_bson`](../../api/basic_json/to_bson.md)                                                                                      | `find(value_type)` and `npos`                                                                                                                                                                |
 | [`parse`](../../api/basic_json/parse.md) from a `string_t`                                                                        | the input adapters must accept it; otherwise pass a character range                                                                                                                          |

docs/mkdocs/docs/integration/compile_times.md

@@ -1,149 +0,0 @@
-# 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

docs/mkdocs/docs/integration/index.md

@@ -15,7 +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 (see [Compile times](compile_times.md)), and file
+for forward declarations, 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).

docs/mkdocs/docs/integration/package_managers.md

@@ -121,10 +121,23 @@ meson wrap install nlohmann_json
 Please see the Meson project for any issues regarding the packaging.
 
 The provided `meson.build` can also be used as an alternative to CMake for installing `nlohmann_json` system-wide in
-which case a pkg-config file is installed. To use it, have your build system require the `nlohmann_json`
+which case a pkg-config file and the CMake package config files are installed. To use it, have your build system require
-pkg-config dependency. In Meson, it is preferred to use the
+the `nlohmann_json` pkg-config dependency, or use [`find_package(nlohmann_json)`](cmake.md#external) in CMake. In Meson,
-[`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a subproject fallback, rather than
+it is preferred to use the [`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a
-using the subproject directly.
+subproject fallback, rather than using the subproject directly.
+
+The options that change the library's configuration are available in Meson as well, named like the
+[CMake options](cmake.md#cmake-options) without the `JSON_` prefix: `MultipleHeaders`, `GlobalUDLs`,
+`ImplicitConversions`, `DisableEnumSerialization`, `Diagnostics`, `Diagnostic_Positions`,
+`LegacyDiscardedValueComparison`, and `StrictNulHandling`. They have the same defaults as in CMake, except that
+`MultipleHeaders` is `false`. Set them with `-D` when setting up the build, or with the subproject name as prefix when
+the library is used as a subproject:
+
+```shell
+meson setup build -Dnlohmann_json:Diagnostics=true
+```
+
+The resulting compile definitions are part of the Meson dependency, the pkg-config file, and the CMake target.
 
 ??? example "Example: Wrap"
 

docs/mkdocs/mkdocs.yml

@@ -106,7 +106,6 @@ 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

include/nlohmann/detail/json_pointer.hpp

@@ -26,6 +26,7 @@
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/string_concat.hpp>
 #include <nlohmann/detail/string_escape.hpp>
+#include <nlohmann/detail/string_utils.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
 NLOHMANN_JSON_NAMESPACE_BEGIN
@@ -116,7 +117,7 @@ class json_pointer
     /// @sa https://json.nlohmann.me/api/json_pointer/operator_slasheq/
     json_pointer& operator/=(std::size_t array_idx)
     {
-        return *this /= std::to_string(array_idx);
+        return *this /= detail::to_string<string_t>(array_idx);
     }
 
     /// @brief create a new JSON pointer by appending the right JSON pointer at the end of the left JSON pointer
@@ -752,7 +753,7 @@ class json_pointer
                         // would throw out_of_range.404 -- contains() must not throw (see #5395)
                         return false;
                     }
-                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !("0" <= reference_token && reference_token <= "9")))
+                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !('0' <= reference_token[0] && reference_token[0] <= '9')))
                     {
                         // invalid char
                         return false;
@@ -780,7 +781,7 @@ class json_pointer
                     // not throw (see #5395), so such a reference token is treated as "not found"
                     errno = 0; // strtoull() does not reset errno on success
                     char* p_end = nullptr; // NOLINT(misc-const-correctness)
-                    const unsigned long long magnitude = std::strtoull(reference_token.c_str(), &p_end, 10); // NOLINT(runtime/int)
+                    const unsigned long long magnitude = std::strtoull(reference_token.data(), &p_end, 10); // NOLINT(runtime/int)
                     if (JSON_HEDLEY_UNLIKELY(errno == ERANGE // the value exceeds ULLONG_MAX
                                              || magnitude >= static_cast<unsigned long long>((std::numeric_limits<typename BasicJsonType::size_type>::max)()))) // NOLINT(runtime/int)
                     {

include/nlohmann/json.hpp

@@ -5092,7 +5092,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @sa https://json.nlohmann.me/api/basic_json/operator_gtgt/
     friend std::istream& operator>>(std::istream& i, basic_json& j)
     {
-        parser(detail::input_adapter(i)).parse(false, j);
+        // parse into a temporary so that j is left unchanged if parsing fails
+        basic_json result;
+        parser(detail::input_adapter(i)).parse(false, result);
+        j = std::move(result);
         return i;
     }
 #endif  // JSON_NO_IO

meson.build

@@ -2,24 +2,111 @@ project('nlohmann_json',
     'cpp',
     version : '3.12.0',
     license : 'MIT',
+    meson_version : '>= 0.64',
+    default_options: ['cpp_std=c++11'],
 )
 
+if get_option('MultipleHeaders')
+    incdir = 'include'
+else
+    incdir = 'single_include'
+endif
+
+# The same compile definitions as the CMake target (see target_compile_definitions
+# in CMakeLists.txt): only an option that differs from its default adds one.
+json_defines = []
+if not get_option('GlobalUDLs')
+    json_defines += 'JSON_USE_GLOBAL_UDLS=0'
+endif
+if not get_option('ImplicitConversions')
+    json_defines += 'JSON_USE_IMPLICIT_CONVERSIONS=0'
+endif
+if get_option('DisableEnumSerialization')
+    json_defines += 'JSON_DISABLE_ENUM_SERIALIZATION=1'
+endif
+if get_option('Diagnostics')
+    json_defines += 'JSON_DIAGNOSTICS=1'
+endif
+if get_option('Diagnostic_Positions')
+    json_defines += 'JSON_DIAGNOSTIC_POSITIONS=1'
+endif
+if get_option('LegacyDiscardedValueComparison')
+    json_defines += 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1'
+endif
+if get_option('StrictNulHandling')
+    json_defines += 'JSON_STRICT_NUL_HANDLING=1'
+endif
+
+cpp_args = []
+foreach define : json_defines
+    cpp_args += '-D' + define
+endforeach
+
 nlohmann_json_dep = declare_dependency(
-    include_directories: include_directories('single_include')
+    compile_args: cpp_args,
+    include_directories: include_directories(incdir)
 )
+meson.override_dependency('nlohmann_json', nlohmann_json_dep)
 
+# The multi-header version under the name earlier versions of this file used
 nlohmann_json_multiple_headers = declare_dependency(
+    compile_args: cpp_args,
     include_directories: include_directories('include')
 )
 
 if not meson.is_subproject()
-install_headers('single_include/nlohmann/json.hpp', subdir: 'nlohmann')
+    install_subdir(
-install_headers('single_include/nlohmann/json_fwd.hpp', subdir: 'nlohmann')
+        incdir / 'nlohmann',
-install_headers('single_include/nlohmann/json_literals.hpp', subdir: 'nlohmann')
+        install_dir: get_option('includedir'),
+        install_tag: 'devel',
+    )
 
-pkgc = import('pkgconfig')
+    pkgc = import('pkgconfig')
-pkgc.generate(name: 'nlohmann_json',
+    pkgc.generate(name: 'nlohmann_json',
-    version: meson.project_version(),
+        version: meson.project_version(),
-    description: 'JSON for Modern C++'
+        description: 'JSON for Modern C++',
-)
+        extra_cflags: cpp_args,
+        install_dir: get_option('datadir') / 'pkgconfig',
+    )
+
+    # CMake package config files, so that find_package(nlohmann_json) works. The
+    # include directory is given relative to the config files, so that the
+    # installation can be relocated. This is not possible if includedir or datadir
+    # is an absolute path outside the prefix (e.g., with the separate outputs of
+    # Nix); then the absolute include directory is used, as CMake does.
+    fs = import('fs')
+    cmake_install_dir = get_option('datadir') / 'cmake' / meson.project_name()
+    cmake_to_prefix = []
+    if fs.is_absolute(get_option('includedir')) or fs.is_absolute(cmake_install_dir)
+        cmake_include_dir = (get_option('prefix') / get_option('includedir')).replace('\\', '/')
+    else
+        foreach component : cmake_install_dir.split('/')
+            cmake_to_prefix += '..'
+        endforeach
+        cmake_include_dir = '${_IMPORT_PREFIX}/' + get_option('includedir')
+    endif
+
+    cmake_conf = configuration_data()
+    cmake_conf.set('PROJECT_NAME', meson.project_name())
+    cmake_conf.set('PROJECT_VERSION', meson.project_version())
+    cmake_conf.set('PROJECT_VERSION_MAJOR', meson.project_version().split('.')[0])
+    cmake_conf.set('NLOHMANN_JSON_TARGET_NAME', meson.project_name())
+    cmake_conf.set('NLOHMANN_JSON_TARGETS_EXPORT_NAME', meson.project_name() + 'Targets')
+    cmake_conf.set('NLOHMANN_JSON_INCLUDE_DIR', cmake_include_dir)
+    cmake_conf.set('NLOHMANN_JSON_CONFIG_TO_PREFIX', '/'.join(cmake_to_prefix))
+    cmake_conf.set('NLOHMANN_JSON_COMPILE_DEFINITIONS', ';'.join(json_defines))
+
+    foreach cmake_file : [
+        ['cmake/config.cmake.in', 'nlohmann_jsonConfig.cmake'],
+        ['cmake/nlohmann_jsonConfigVersion.cmake.in', 'nlohmann_jsonConfigVersion.cmake'],
+        ['cmake/nlohmann_jsonTargets.cmake.in', 'nlohmann_jsonTargets.cmake'],
+    ]
+        configure_file(
+            input: cmake_file[0],
+            output: cmake_file[1],
+            configuration: cmake_conf,
+            format: 'cmake@',
+            install_dir: cmake_install_dir,
+        )
+    endforeach
 endif

meson_options.txt

@@ -0,0 +1,48 @@
+option(
+    'MultipleHeaders',
+    type: 'boolean',
+    value: false,
+    description: 'Use non-amalgamated version of the library',
+)
+option(
+    'GlobalUDLs',
+    type: 'boolean',
+    value: true,
+    description: 'Place user-defined string literals in the global namespace',
+)
+option(
+    'ImplicitConversions',
+    type: 'boolean',
+    value: true,
+    description: 'Enable implicit conversions',
+)
+option(
+    'DisableEnumSerialization',
+    type: 'boolean',
+    value: false,
+    description: 'Disable default integer enum serialization',
+)
+option(
+    'Diagnostics',
+    type: 'boolean',
+    value: false,
+    description: 'Use extended diagnostic messages',
+)
+option(
+    'Diagnostic_Positions',
+    type: 'boolean',
+    value: false,
+    description: 'Enable diagnostic positions',
+)
+option(
+    'LegacyDiscardedValueComparison',
+    type: 'boolean',
+    value: false,
+    description: 'Enable legacy discarded value comparison',
+)
+option(
+    'StrictNulHandling',
+    type: 'boolean',
+    value: false,
+    description: 'Enable strict NUL-byte handling',
+)

single_include/nlohmann/json.hpp

@@ -19636,6 +19636,8 @@ NLOHMANN_JSON_NAMESPACE_END
 
 // #include <nlohmann/detail/string_escape.hpp>
 
+// #include <nlohmann/detail/string_utils.hpp>
+
 // #include <nlohmann/detail/value_t.hpp>
 
 
@@ -19727,7 +19729,7 @@ class json_pointer
     /// @sa https://json.nlohmann.me/api/json_pointer/operator_slasheq/
     json_pointer& operator/=(std::size_t array_idx)
     {
-        return *this /= std::to_string(array_idx);
+        return *this /= detail::to_string<string_t>(array_idx);
     }
 
     /// @brief create a new JSON pointer by appending the right JSON pointer at the end of the left JSON pointer
@@ -20363,7 +20365,7 @@ class json_pointer
                         // would throw out_of_range.404 -- contains() must not throw (see #5395)
                         return false;
                     }
-                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !("0" <= reference_token && reference_token <= "9")))
+                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !('0' <= reference_token[0] && reference_token[0] <= '9')))
                     {
                         // invalid char
                         return false;
@@ -20391,7 +20393,7 @@ class json_pointer
                     // not throw (see #5395), so such a reference token is treated as "not found"
                     errno = 0; // strtoull() does not reset errno on success
                     char* p_end = nullptr; // NOLINT(misc-const-correctness)
-                    const unsigned long long magnitude = std::strtoull(reference_token.c_str(), &p_end, 10); // NOLINT(runtime/int)
+                    const unsigned long long magnitude = std::strtoull(reference_token.data(), &p_end, 10); // NOLINT(runtime/int)
                     if (JSON_HEDLEY_UNLIKELY(errno == ERANGE // the value exceeds ULLONG_MAX
                                              || magnitude >= static_cast<unsigned long long>((std::numeric_limits<typename BasicJsonType::size_type>::max)()))) // NOLINT(runtime/int)
                     {
@@ -32017,7 +32019,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @sa https://json.nlohmann.me/api/basic_json/operator_gtgt/
     friend std::istream& operator>>(std::istream& i, basic_json& j)
     {
-        parser(detail::input_adapter(i)).parse(false, j);
+        // parse into a temporary so that j is left unchanged if parsing fails
+        basic_json result;
+        parser(detail::input_adapter(i)).parse(false, result);
+        j = std::move(result);
         return i;
     }
 #endif  // JSON_NO_IO

tests/src/unit-alt-string.cpp

@@ -352,6 +352,41 @@ TEST_CASE("alternative string type")
         CHECK(j2.flatten().unflatten() == j2);
     }
 
+    SECTION("contains(json_pointer)")
+    {
+        // contains(json_pointer) must compile and work with a string_t that has
+        // no c_str() and no comparison with const char* (see #5666)
+        auto j = alt_json::parse(R"({"foo": ["bar", "baz"]})");
+
+        // present: object key and array indices
+        CHECK(j.contains(alt_json::json_pointer("/foo")));
+        CHECK(j.contains(alt_json::json_pointer("/foo/0")));
+        CHECK(j.contains(alt_json::json_pointer("/foo/1")));
+
+        // missing: absent object key and out-of-range array index
+        CHECK_FALSE(j.contains(alt_json::json_pointer("/bar")));
+        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/2")));
+
+        // "-" always fails the range check
+        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/-")));
+
+        // an array index must not have a leading zero
+        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/01")));
+
+        // a reference token that is not a number
+        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/bar")));
+    }
+
+    SECTION("operator/(std::size_t)")
+    {
+        // json_pointer::operator/=(std::size_t) must compile without string_t
+        // being constructible from std::string (see #5666)
+        auto j = alt_json::parse(R"({"foo": ["bar", "baz"]})");
+
+        CHECK(j.at(alt_json::json_pointer("/foo") / std::size_t(0)) == j["foo"][0]);
+        CHECK(j.at(alt_json::json_pointer("/foo") / std::size_t(1)) == j["foo"][1]);
+    }
+
     SECTION("patch")
     {
         alt_json const patch1 = alt_json::parse(R"([{ "op": "add", "path": "/a/b", "value": [ "foo", "bar" ] }])");

tests/src/unit-diagnostics.cpp

@@ -19,6 +19,7 @@ using nlohmann::json;
 
 #include <map>
 #include <unordered_map>
+#include <sstream>
 
 TEST_CASE("Better diagnostics")
 {
@@ -492,6 +493,21 @@ TEST_CASE("Regression tests for extended diagnostics")
             CHECK(copy == j);
         }
     }
+
+    SECTION("Regression test for issue #5652 - operator>> leaves a partial value in its target on a parse error")
+    {
+        json j = "old value";
+        std::istringstream is("[1, x");
+        CHECK_THROWS_WITH_AS(is >> j, "[json.exception.parse_error.101] parse error at line 1, column 5: syntax error while parsing value - invalid literal; last read: '1, x'", json::parse_error);
+
+        // j must be left unchanged, as json::parse() guarantees for its result
+        CHECK(j == "old value");
+
+        // copying j must not trigger assert_invariant(): a failed parse must
+        // not leave array/object elements without a parent pointer
+        json const copy = j; // NOLINT(performance-unnecessary-copy-initialization)
+        CHECK(copy == j);
+    }
 }
 
 TEST_CASE("Better diagnostics past the descent bound of update() and merge_patch()")