Merge branch 'develop' into claude/string-view-convertible-keys-5663

Conflicts:
- docs/mkdocs/docs/api/basic_json/count.md: kept the PR's string_view note on overload 2 and develop's new item 3 (deleted integral-key overload)
- docs/mkdocs/docs/api/basic_json/find.md: same as count.md
- docs/mkdocs/docs/api/basic_json/value.md: kept develop's integral-key note on item 1 and the PR's string_view note on item 2

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

.github/workflows/ubuntu.yml

@@ -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:

CMakeLists.txt

@@ -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"

FILES.md

@@ -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`
 

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 meson_options.txt 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

cmake/nlohmann_jsonTargets.cmake.in

@@ -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)

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}@NLOHMANN_JSON_PKGCONFIG_CFLAGS@
+Cflags: -I${includedir}

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

@@ -224,5 +224,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
 
 1. Added in version 1.0.0.
 2. Added in version 1.0.0.
-3. Added in version 3.11.0.
+3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
+   already supported by [`operator[]`](operator[].md), [`value`](value.md), [`find`](find.md), and other lookup
+   functions.
 4. Added in version 2.0.0.

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

@@ -119,7 +119,9 @@ Logarithmic in the size of the JSON object.
 ## Version history
 
 1. Added in version 3.11.0.
-2. Added in version 3.6.0. Extended template `KeyType` to support comparable types in version 3.11.0.
+2. Added in version 3.6.0. Extended template `KeyType` to support comparable types in version 3.11.0. Fixed in
+   version 3.13.0 to consistently accept `std::string_view`-convertible keys, as already supported by
+   [`operator[]`](operator[].md), [`at`](at.md), [`value`](value.md), and other lookup functions.
 3. Added in version 3.7.0.
 4. Deleted overloads for integral key types added in version 3.13.0 to reject such calls at compile time instead of
    causing undefined behavior at runtime.

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

@@ -84,6 +84,8 @@ Logarithmic in the size of the JSON object.
 ## Version history
 
 1. Added in version 3.11.0.
-2. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0.
+2. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0. Fixed in version 3.13.0 to
+   consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](operator[].md),
+   [`at`](at.md), [`value`](value.md), and other lookup functions.
 3. Deleted overload for integral key types added in version 3.13.0 to reject such calls at compile time instead of
    causing undefined behavior at runtime.

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

@@ -213,5 +213,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
 1. Added in version 1.0.0. Added support for binary types in version 3.8.0.
 2. Added in version 1.0.0. Added support for binary types in version 3.8.0.
 3. Added in version 1.0.0.
-4. Added in version 3.11.0.
+4. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
+   already supported by [`operator[]`](operator[].md), [`at`](at.md), [`value`](value.md), and other lookup
+   functions.
 5. Added in version 1.0.0.

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

@@ -88,6 +88,8 @@ Logarithmic in the size of the JSON object.
 ## Version history
 
 1. Added in version 3.11.0.
-2. Added in version 1.0.0. Changed to support comparable types in version 3.11.0.
+2. Added in version 1.0.0. Changed to support comparable types in version 3.11.0. Fixed in version 3.13.0 to
+   consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](operator[].md),
+   [`at`](at.md), [`value`](value.md), and other lookup functions.
 3. Deleted overloads for integral key types added in version 3.13.0 to reject such calls at compile time instead of
    causing undefined behavior at runtime.

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

@@ -195,7 +195,9 @@ changes to any JSON value.
 1. Added in version 1.0.0. Changed parameter `default_value` type from `const ValueType&` to `ValueType&&` in version
    3.11.0. Deleted overload for integral key types added in version 3.13.0 to reject such calls at compile time
    instead of causing undefined behavior at runtime.
-2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2.
+2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2. Fixed in version 3.13.0
+   to consistently accept `std::string_view`-convertible keys, as already supported by
+   [`operator[]`](operator[].md), [`at`](at.md), [`find`](find.md), and other lookup functions.
 3. Added in version 2.0.2. Extended to work with arrays in version 3.13.0, including fixing an issue where resolving
    `ptr` through an array unexpectedly threw `out_of_range` instead of returning the resolved element (or
    `default_value`, as documented).

docs/mkdocs/docs/integration/package_managers.md

@@ -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"
 

include/nlohmann/detail/meta/type_traits.hpp

@@ -748,6 +748,30 @@ using is_usable_as_key_type = typename std::conditional <
                               std::true_type,
                               std::false_type >::type;
 
+#ifdef JSON_HAS_CPP_17
+// type trait to check if KeyType can only be used as an object key after
+// converting it to std::string_view: it is convertible to std::string_view, the
+// object's comparator cannot compare it with object_t::key_type directly, but
+// can compare a std::string_view. JSON pointers and JSON iterators are ruled out
+// first, so that the conversion checks are never instantiated for them (a JSON
+// pointer's deprecated conversion to string_t would be named otherwise).
+template < typename BasicJsonType, typename KeyTypeCVRef, typename KeyType = uncvref_t<KeyTypeCVRef>,
+           bool = is_json_pointer<KeyType>::value || is_json_iterator_of<BasicJsonType, KeyType>::value >
+struct is_string_view_convertible_key_type : std::false_type {};
+
+template<typename BasicJsonType, typename KeyTypeCVRef, typename KeyType>
+struct is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef, KeyType, false>
+    : std::integral_constant < bool,
+      std::is_convertible<KeyTypeCVRef, std::string_view>::value
+      && !is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
+      typename BasicJsonType::object_t::key_type, KeyTypeCVRef, true, false>::value
+      && is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
+      typename BasicJsonType::object_t::key_type, std::string_view, true, false>::value > {};
+#else
+template<typename BasicJsonType, typename KeyTypeCVRef>
+struct is_string_view_convertible_key_type : std::false_type {};
+#endif
+
 // type trait to check if KeyType can be used as an object key
 // true if:
 //   - KeyType is comparable with BasicJsonType::object_t::key_type
@@ -761,9 +785,7 @@ using is_usable_as_basic_json_key_type = typename std::conditional <
      typename BasicJsonType::object_t::key_type, KeyTypeCVRef,
      RequireTransparentComparator, ExcludeObjectKeyType>::value
      && !is_json_iterator_of<BasicJsonType, KeyType>::value)
-#ifdef JSON_HAS_CPP_17
-    || std::is_convertible<KeyType, std::string_view>::value
-#endif
+    || is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef>::value
     , std::true_type,
     std::false_type >::type;
 

include/nlohmann/json.hpp

@@ -807,6 +807,24 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return it;
     }
 
+    /// @brief the key to look up an object member with: the key itself, or its
+    ///        std::string_view if the object can only be searched with that
+    template < typename KeyType, detail::enable_if_t <
+                   !detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
+    static KeyType && lookup_key(KeyType && key) noexcept
+    {
+        return std::forward<KeyType>(key);
+    }
+
+#ifdef JSON_HAS_CPP_17
+    template < typename KeyType, detail::enable_if_t <
+                   detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
+    static std::string_view lookup_key(KeyType && key)
+    {
+        return std::forward<KeyType>(key);
+    }
+#endif
+
     /// @brief erase an element from the object and return the following one
     /// Not every map returns an iterator from erase(iterator): some containers
     /// (e.g., Abseil's hash maps) return void to avoid computing a successor
@@ -2767,7 +2785,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -2805,7 +2823,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -2948,7 +2966,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto result = m_data.m_value.object->emplace(std::forward<KeyType>(key), nullptr);
+            auto result = m_data.m_value.object->emplace(lookup_key(std::forward<KeyType>(key)), nullptr);
             return set_parent(result.first->second);
         }
 
@@ -2964,7 +2982,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // const operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+            auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
             JSON_ASSERT(it != m_data.m_value.object->end());
             return it->second;
         }
@@ -2974,8 +2992,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
   private:
     template<typename KeyType>
-    using is_comparable_with_object_key = detail::is_comparable <
-        object_comparator_t, const typename object_t::key_type&, KeyType >;
+    using is_comparable_with_object_key = std::integral_constant < bool,
+        detail::is_comparable <
+            object_comparator_t, const typename object_t::key_type&, KeyType >::value
+        || detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value >;
 
     template<typename ValueType>
     using value_return_type = std::conditional <
@@ -3362,7 +3382,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(307, detail::concat("cannot use erase() with ", type_name()), this));
         }
 
-        const auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+        const auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         if (it != m_data.m_value.object->end())
         {
             m_data.m_value.object->erase(it);
@@ -3389,7 +3409,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  detail::is_usable_as_basic_json_key_type<basic_json_t, KeyType>::value, int> = 0>
     size_type erase(KeyType && key)
     {
-        return erase_internal(std::forward<KeyType>(key));
+        return erase_internal(lookup_key(std::forward<KeyType>(key)));
     }
 
     /// @brief remove element from a JSON array given an index
@@ -3469,7 +3489,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
+            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         }
 
         return result;
@@ -3485,7 +3505,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
+            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         }
 
         return result;
@@ -3508,7 +3528,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     size_type count(KeyType && key) const
     {
         // return 0 for all nonobject types
-        return is_object() ? m_data.m_value.object->count(std::forward<KeyType>(key)) : 0;
+        return is_object() ? m_data.m_value.object->count(lookup_key(std::forward<KeyType>(key))) : 0;
     }
 
     /// @brief check the existence of an element in a JSON object
@@ -3526,7 +3546,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     bool contains(KeyType && key) const
     {
-        return is_object() && m_data.m_value.object->find(std::forward<KeyType>(key)) != m_data.m_value.object->end();
+        return is_object() && m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key))) != m_data.m_value.object->end();
     }
 
     /// @brief check the existence of an element in a JSON object given a JSON pointer

meson.build

@@ -2,111 +2,24 @@ 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')
+install_headers('single_include/nlohmann/json_literals.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

meson_options.txt

@@ -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',
-)

single_include/nlohmann/json.hpp

@@ -4756,6 +4756,30 @@ using is_usable_as_key_type = typename std::conditional <
                               std::true_type,
                               std::false_type >::type;
 
+#ifdef JSON_HAS_CPP_17
+// type trait to check if KeyType can only be used as an object key after
+// converting it to std::string_view: it is convertible to std::string_view, the
+// object's comparator cannot compare it with object_t::key_type directly, but
+// can compare a std::string_view. JSON pointers and JSON iterators are ruled out
+// first, so that the conversion checks are never instantiated for them (a JSON
+// pointer's deprecated conversion to string_t would be named otherwise).
+template < typename BasicJsonType, typename KeyTypeCVRef, typename KeyType = uncvref_t<KeyTypeCVRef>,
+           bool = is_json_pointer<KeyType>::value || is_json_iterator_of<BasicJsonType, KeyType>::value >
+struct is_string_view_convertible_key_type : std::false_type {};
+
+template<typename BasicJsonType, typename KeyTypeCVRef, typename KeyType>
+struct is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef, KeyType, false>
+    : std::integral_constant < bool,
+      std::is_convertible<KeyTypeCVRef, std::string_view>::value
+      && !is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
+      typename BasicJsonType::object_t::key_type, KeyTypeCVRef, true, false>::value
+      && is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
+      typename BasicJsonType::object_t::key_type, std::string_view, true, false>::value > {};
+#else
+template<typename BasicJsonType, typename KeyTypeCVRef>
+struct is_string_view_convertible_key_type : std::false_type {};
+#endif
+
 // type trait to check if KeyType can be used as an object key
 // true if:
 //   - KeyType is comparable with BasicJsonType::object_t::key_type
@@ -4769,9 +4793,7 @@ using is_usable_as_basic_json_key_type = typename std::conditional <
      typename BasicJsonType::object_t::key_type, KeyTypeCVRef,
      RequireTransparentComparator, ExcludeObjectKeyType>::value
      && !is_json_iterator_of<BasicJsonType, KeyType>::value)
-#ifdef JSON_HAS_CPP_17
-    || std::is_convertible<KeyType, std::string_view>::value
-#endif
+    || is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef>::value
     , std::true_type,
     std::false_type >::type;
 
@@ -27734,6 +27756,24 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return it;
     }
 
+    /// @brief the key to look up an object member with: the key itself, or its
+    ///        std::string_view if the object can only be searched with that
+    template < typename KeyType, detail::enable_if_t <
+                   !detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
+    static KeyType && lookup_key(KeyType && key) noexcept
+    {
+        return std::forward<KeyType>(key);
+    }
+
+#ifdef JSON_HAS_CPP_17
+    template < typename KeyType, detail::enable_if_t <
+                   detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
+    static std::string_view lookup_key(KeyType && key)
+    {
+        return std::forward<KeyType>(key);
+    }
+#endif
+
     /// @brief erase an element from the object and return the following one
     /// Not every map returns an iterator from erase(iterator): some containers
     /// (e.g., Abseil's hash maps) return void to avoid computing a successor
@@ -29694,7 +29734,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -29732,7 +29772,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -29875,7 +29915,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto result = m_data.m_value.object->emplace(std::forward<KeyType>(key), nullptr);
+            auto result = m_data.m_value.object->emplace(lookup_key(std::forward<KeyType>(key)), nullptr);
             return set_parent(result.first->second);
         }
 
@@ -29891,7 +29931,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // const operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+            auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
             JSON_ASSERT(it != m_data.m_value.object->end());
             return it->second;
         }
@@ -29901,8 +29941,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
   private:
     template<typename KeyType>
-    using is_comparable_with_object_key = detail::is_comparable <
-        object_comparator_t, const typename object_t::key_type&, KeyType >;
+    using is_comparable_with_object_key = std::integral_constant < bool,
+        detail::is_comparable <
+            object_comparator_t, const typename object_t::key_type&, KeyType >::value
+        || detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value >;
 
     template<typename ValueType>
     using value_return_type = std::conditional <
@@ -30289,7 +30331,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(307, detail::concat("cannot use erase() with ", type_name()), this));
         }
 
-        const auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
+        const auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         if (it != m_data.m_value.object->end())
         {
             m_data.m_value.object->erase(it);
@@ -30316,7 +30358,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  detail::is_usable_as_basic_json_key_type<basic_json_t, KeyType>::value, int> = 0>
     size_type erase(KeyType && key)
     {
-        return erase_internal(std::forward<KeyType>(key));
+        return erase_internal(lookup_key(std::forward<KeyType>(key)));
     }
 
     /// @brief remove element from a JSON array given an index
@@ -30396,7 +30438,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
+            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         }
 
         return result;
@@ -30412,7 +30454,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
+            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
         }
 
         return result;
@@ -30435,7 +30477,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     size_type count(KeyType && key) const
     {
         // return 0 for all nonobject types
-        return is_object() ? m_data.m_value.object->count(std::forward<KeyType>(key)) : 0;
+        return is_object() ? m_data.m_value.object->count(lookup_key(std::forward<KeyType>(key))) : 0;
     }
 
     /// @brief check the existence of an element in a JSON object
@@ -30453,7 +30495,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     bool contains(KeyType && key) const
     {
-        return is_object() && m_data.m_value.object->find(std::forward<KeyType>(key)) != m_data.m_value.object->end();
+        return is_object() && m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key))) != m_data.m_value.object->end();
     }
 
     /// @brief check the existence of an element in a JSON object given a JSON pointer

tests/src/unit-element_access2.cpp

@@ -1973,4 +1973,115 @@ TEST_CASE("operator[] with user-defined std::string_view-convertible types")
         }
     }
 }
+
+TEST_CASE("keys convertible to std::string_view work with all lookup functions (regression test for #5663)")
+{
+    // a key type convertible only to std::string_view: the case #4958 added
+    // support for, but only the non-const operator[] compiled with it
+    struct ViewKey
+    {
+        operator std::string_view() const
+        {
+            return "a";
+        }
+    };
+
+    // a key type convertible to both std::string and std::string_view: with
+    // 3.12.0, such a key worked with at, the const operator[], find, count and
+    // contains via the conversion to std::string; #4958 made the KeyType&&
+    // templates win overload resolution for it instead, and those then failed
+    struct DualKey
+    {
+        operator std::string() const
+        {
+            return "a";
+        }
+        operator std::string_view() const
+        {
+            return "a";
+        }
+    };
+
+    SECTION("nlohmann::json")
+    {
+        using json = nlohmann::json;
+
+        SECTION("ViewKey")
+        {
+            json j = {{"a", 1}};
+            const json& cj = j;
+
+            CHECK(j[ViewKey{}] == 1);
+            CHECK(cj[ViewKey{}] == 1);
+            CHECK(j.at(ViewKey{}) == 1);
+            CHECK(cj.at(ViewKey{}) == 1);
+            CHECK(j.find(ViewKey{}) != j.end());
+            CHECK(cj.find(ViewKey{}) != cj.end());
+            CHECK(j.count(ViewKey{}) == 1);
+            CHECK(j.contains(ViewKey{}));
+            CHECK(j.value(ViewKey{}, 0) == 1);
+            CHECK(j.erase(ViewKey{}) == 1);
+            CHECK(!j.contains("a"));
+        }
+
+        SECTION("DualKey")
+        {
+            json j = {{"a", 1}};
+            const json& cj = j;
+
+            CHECK(j[DualKey{}] == 1);
+            CHECK(cj[DualKey{}] == 1);
+            CHECK(j.at(DualKey{}) == 1);
+            CHECK(cj.at(DualKey{}) == 1);
+            CHECK(j.find(DualKey{}) != j.end());
+            CHECK(cj.find(DualKey{}) != cj.end());
+            CHECK(j.count(DualKey{}) == 1);
+            CHECK(j.contains(DualKey{}));
+            CHECK(j.value(DualKey{}, 0) == 1);
+            CHECK(j.erase(DualKey{}) == 1);
+            CHECK(!j.contains("a"));
+        }
+    }
+
+    SECTION("nlohmann::ordered_json")
+    {
+        using ordered_json = nlohmann::ordered_json;
+
+        SECTION("ViewKey")
+        {
+            ordered_json j = {{"a", 1}};
+            const ordered_json& cj = j;
+
+            CHECK(j[ViewKey{}] == 1);
+            CHECK(cj[ViewKey{}] == 1);
+            CHECK(j.at(ViewKey{}) == 1);
+            CHECK(cj.at(ViewKey{}) == 1);
+            CHECK(j.find(ViewKey{}) != j.end());
+            CHECK(cj.find(ViewKey{}) != cj.end());
+            CHECK(j.count(ViewKey{}) == 1);
+            CHECK(j.contains(ViewKey{}));
+            CHECK(j.value(ViewKey{}, 0) == 1);
+            CHECK(j.erase(ViewKey{}) == 1);
+            CHECK(!j.contains("a"));
+        }
+
+        SECTION("DualKey")
+        {
+            ordered_json j = {{"a", 1}};
+            const ordered_json& cj = j;
+
+            CHECK(j[DualKey{}] == 1);
+            CHECK(cj[DualKey{}] == 1);
+            CHECK(j.at(DualKey{}) == 1);
+            CHECK(cj.at(DualKey{}) == 1);
+            CHECK(j.find(DualKey{}) != j.end());
+            CHECK(cj.find(DualKey{}) != cj.end());
+            CHECK(j.count(DualKey{}) == 1);
+            CHECK(j.contains(DualKey{}));
+            CHECK(j.value(DualKey{}, 0) == 1);
+            CHECK(j.erase(DualKey{}) == 1);
+            CHECK(!j.contains("a"));
+        }
+    }
+}
 #endif