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

* 📝 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
@@ -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