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Author SHA1 Message Date
Niels Lohmann 4494890be6 Merge branch 'develop' into claude/issue-5066-24ba30
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-27 20:57:55 +02:00
Niels Lohmann c4469c9f82 Add regression test for converting json to std::variant<json> (#5066)
With 3.10.5, get<std::variant<json>>() was well-formed through the string
from_json overload, so the implicit conversion operator was a candidate
when converting json to std::variant<json>, and MSVC picked it over the
variant's converting constructor. The tightened constraints from #3427 and
#3604 (3.11.0) removed that path; this test guards against regressions.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-27 16:49:33 +02:00
10 changed files with 31 additions and 286 deletions
-39
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@@ -31,45 +31,6 @@ 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:
+1 -24
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@@ -168,30 +168,7 @@ if (MSVC)
)
endif()
# 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()
# Install a pkg-config file, so other tools can find this.
configure_file(
"${CMAKE_CURRENT_SOURCE_DIR}/cmake/pkg-config.pc.in"
"${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
+2 -22
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@@ -260,29 +260,9 @@ make BUILD.bazel
The "Check amalgamation" workflow fails if the file is out of date.
### `meson.build` and `meson_options.txt`
### `meson.build`
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.
The build definition for the [Meson](https://mesonbuild.com) build system.
### `Package.swift`
+1 -1
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@@ -222,7 +222,7 @@ 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 meson_options.txt LICENSE.MIT
zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) BUILD.bazel MODULE.bazel meson.build LICENSE.MIT
# Create the files for a release and add signatures and hashes.
release: include.zip json.tar.xz
-38
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@@ -1,38 +0,0 @@
# Imported target for installations made with Meson (see meson.build).
#
# CMake installations generate this file with install(EXPORT ...). Meson cannot
# do that, but as the library is header-only, the target only needs an include
# directory, the C++ standard, and the compile definitions of the options that
# differ from their defaults. Paths are computed relative to this file so that
# the installation can be relocated (e.g., into a sysroot), unless includedir or
# datadir is outside the prefix.
if(TARGET @PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@)
return()
endif()
get_filename_component(_IMPORT_PREFIX "${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 "${_NLOHMANN_JSON_COMPILE_DEFINITIONS}"
)
endif()
unset(_NLOHMANN_JSON_COMPILE_DEFINITIONS)
unset(_IMPORT_PREFIX)
+1 -1
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@@ -4,4 +4,4 @@ includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
Name: @PROJECT_NAME@
Description: JSON for Modern C++
Version: @PROJECT_VERSION@
Cflags: -I${includedir}@NLOHMANN_JSON_PKGCONFIG_CFLAGS@
Cflags: -I${includedir}
@@ -121,23 +121,10 @@ 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 and the CMake package config files are installed. To use it, have your build system require
the `nlohmann_json` pkg-config dependency, or use [`find_package(nlohmann_json)`](cmake.md#external) in CMake. In Meson,
it is preferred to use the [`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a
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.
which case a pkg-config file is installed. To use it, have your build system require the `nlohmann_json`
pkg-config dependency. In Meson, it is preferred to use the
[`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a subproject fallback, rather than
using the subproject directly.
??? example "Example: Wrap"
+8 -96
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@@ -2,111 +2,23 @@ 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(
compile_args: cpp_args,
include_directories: include_directories(incdir)
include_directories: include_directories('single_include')
)
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_subdir(
incdir / 'nlohmann',
install_dir: get_option('includedir'),
install_tag: 'devel',
)
install_headers('single_include/nlohmann/json.hpp', subdir: 'nlohmann')
install_headers('single_include/nlohmann/json_fwd.hpp', subdir: 'nlohmann')
pkgc = import('pkgconfig')
pkgc.generate(name: 'nlohmann_json',
version: meson.project_version(),
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
pkgc = import('pkgconfig')
pkgc.generate(name: 'nlohmann_json',
version: meson.project_version(),
description: 'JSON for Modern C++'
)
endif
-48
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@@ -1,48 +0,0 @@
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',
)
+14
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@@ -766,6 +766,20 @@ TEST_CASE("regression tests 2")
CHECK(j == k);
}
#ifdef JSON_HAS_CPP_17
SECTION("issue #5066 - MSVC converts json to std::variant<json> via the conversion operator")
{
// std::variant<json> must not be retrievable via get<>(), because otherwise the
// implicit conversion operator becomes a candidate that MSVC picks over the variant's
// converting constructor, routing a number through the string from_json overload
static_assert(!nlohmann::detail::is_detected<nlohmann::detail::get_template_function, const json&, std::variant<json>>::value,
"std::variant<json> must not be retrievable via get<>()");
std::vector<std::variant<json>> v;
v.push_back(json(1));
CHECK(std::get<0>(v[0]) == 1);
}
#endif
}
TEST_CASE("regression test - parser callback must not lose a duplicate key's prior value")