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Address -Wpragma-clang-attribute #2297

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Address -Wpragma-clang-attribute #2297

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Address -Wpragma-clang-attribute
ispeters Oct 2, 2026
e9d7af3
Merge remote-tracking branch 'origin/main' into address-unused-attribute
ericniebler Oct 4, 2026
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27 changes: 26 additions & 1 deletion include/stdexec/__detail/__config.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -180,7 +180,32 @@ import std;
// library. It is used when forward-declaring a standard library type or
// function, which is not portable but sometimes necessary to avoid pulling in a
// large header when a fwd decl would do.
#if defined(_LIBCPP_VERSION)
//
// libc++ 23's _LIBCPP_BEGIN_NAMESPACE_STD opens a `#pragma clang attribute
// push` region that applies only to functions, and _LIBCPP_END_NAMESPACE_STD
// closes it. When the region is opened from a non-system header and declares no
// functions (as in our forward-declaration blocks), Clang reports the pushed
// attribute as unused under -Wpragma-clang-attribute, so we suppress that
// warning for the duration of the block. Only Clang implements `#pragma clang
// attribute`, so only Clang can emit that warning; hence the STDEXEC_CLANG()
// guard.
//
// Known gap: libc++ 23 emits those pragmas for every compiler (later versions
// emit them only for Clang-based compilers), so GCC with libc++ 23 reports them
// under -Wunknown-pragmas instead. GCC does not apply a diagnostic pragma to
// another pragma from the same macro expansion, so that can't be suppressed
// here.
//
// This uses STDEXEC_PRAGMA directly rather than STDEXEC_PRAGMA_PUSH() and
// friends because those are defined further down, after the first use of these
// macros below.
#if defined(_LIBCPP_VERSION) && STDEXEC_CLANG()
# define STDEXEC_NAMESPACE_STD_BEGIN \
STDEXEC_PRAGMA(clang diagnostic push) \
STDEXEC_PRAGMA(clang diagnostic ignored "-Wpragma-clang-attribute") \
_LIBCPP_BEGIN_NAMESPACE_STD
# define STDEXEC_NAMESPACE_STD_END _LIBCPP_END_NAMESPACE_STD STDEXEC_PRAGMA(clang diagnostic pop)
#elif defined(_LIBCPP_VERSION)
# define STDEXEC_NAMESPACE_STD_BEGIN _LIBCPP_BEGIN_NAMESPACE_STD
# define STDEXEC_NAMESPACE_STD_END _LIBCPP_END_NAMESPACE_STD
#elif defined(__GLIBCXX__)
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