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Document compiler/stdlib exclusions in macro_scope.hpp (#5252)

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* 📝 Document compiler/stdlib exclusions in macro_scope.hpp

Add "Known compiler/stdlib exclusions" subsections to the public documentation for
JSON_HAS_FILESYSTEM and JSON_HAS_RANGES, listing the exact compiler/stdlib versions
that are silently excluded even when feature-test macros indicate support. Each
exclusion references the originating issue. Also add a pointer note in the compiler
compatibility section linking to these details.

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

* 💚 fix build

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Code <noreply@anthropic.com>
This commit is contained in:
Niels Lohmann
2026-07-09 17:15:57 +02:00
committed by GitHub
co-authored by Claude Code
parent ff34a3fd2f
commit ca91678af1
3 changed files with 28 additions and 0 deletions
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docs/mkdocs/docs/api/macros/json_has_filesystem.md
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@@ -19,6 +19,20 @@ The default value is detected based on the preprocessor macros `#!cpp __cpp_lib_
`#!cpp __cpp_lib_experimental_filesystem`, `#!cpp __has_include(<filesystem>)`, or
`#!cpp __has_include(<experimental/filesystem>)`.
!!! info "Known compiler/stdlib exclusions"
Even when the feature-test macro indicates filesystem support is available, the library disables it on the following broken toolchains:
- **MinGW + GCC 8** — disabled entirely (broken `std::filesystem` implementation; [MinGW-w64 bug 737](https://sourceforge.net/p/mingw-w64/bugs/737/))
- **GCC (non-Clang) < 8** — disabled (no filesystem support)
- **Clang < 7** — disabled (no filesystem support)
- **MSVC < 19.14** — disabled (no filesystem support)
- **iOS < 13** — disabled (no filesystem support)
- **macOS < Catalina (10.15)** — disabled (no filesystem support)
If `JSON_HAS_FILESYSTEM` or `JSON_HAS_EXPERIMENTAL_FILESYSTEM` is `0` despite `__cpp_lib_filesystem` being defined, one
of the exclusions above likely applies to your toolchain.
## Notes
- Note that older compilers or older versions of libstdc++ also require the library `stdc++fs` to be linked to for
docs/mkdocs/docs/api/macros/json_has_ranges.md
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@@ -13,6 +13,18 @@ The default value is detected based on the preprocessor macro `#!cpp __cpp_lib_r
When the macro is not defined, the library will define it to its default value.
!!! info "Known compiler/stdlib exclusions"
Even when the feature-test macro `__cpp_lib_ranges` indicates ranges support is available, the library disables it on
the following incomplete or broken toolchains:
- **GCC 11.1.0** — disabled (the shipped `<ranges>` header has a syntax error; [issue #4440](https://github.com/nlohmann/json/issues/4440))
- **libstdc++ < 11** — disabled (incomplete C++20 ranges support; [issue #4440](https://github.com/nlohmann/json/issues/4440))
- **Clang < 16 with libstdc++** — disabled (incomplete ranges support; [issue #4440](https://github.com/nlohmann/json/issues/4440))
- **libc++ < 160000** — disabled (incomplete C++20 ranges support; [issue #4440](https://github.com/nlohmann/json/issues/4440))
If `JSON_HAS_RANGES` is `0` despite `__cpp_lib_ranges` being defined, one of the exclusions above likely applies to your toolchain.
## Examples
??? example