From: Jonathan Wakely Date: Fri, 9 May 2025 09:23:05 +0000 (+0100) Subject: libstdc++: Remove #warning from for C++17 [PR120187] X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=af062510f4179aa7b13e632f77593deee8fe29f2;p=thirdparty%2Fgcc.git libstdc++: Remove #warning from for C++17 [PR120187] Although was removed from C++20, it was not formally deprecated in C++17. In contrast, , , etc. were formally deprecated in C++17 before being removed in C++20. Due to the widespread convention of including to detect implementation-specific macros (such as _GLIBCXX_RELEASE) it causes quite a lot of noise to issue deprecation warnings in C++17 mode. The recommendation to include instead does work for recent compilers, even in C++17 mode, but isn't portable to older compilers that don't provide yet (e.g. GCC 8). There are also potential objections to including pre-C++20 when it wasn't defined by the standard. I don't have much sympathy for this position, because including for implementation-specific macros wasn't part of the C++17 standard either. It's no more non-standard to rely on being present and defining those macros than to rely on defining them, and __has_include can be used to detect whether is present. However, is being used in the wild by popular libraries like Abseil and we can't change versions of those that have already been released. This removes the #warning in for C++17 mode, so that we only emit diagnostics for C++20 and later. With this change, including in C++20 or later gives an error if _GLIBCXX_USE_DEPRECATED is defined to zero, otherwise a warning if -Wdeprecated is enabled, otherwise no diagnostic is given. This also adds "@since C++11 (removed in C++20)" to the Doxygen @file comments in all the relevant headers. The test for needs to be updated to no longer expect a warning for c++17_only. A new test is added to ensure that we get a warning instead of an error when -D_GLIBCXX_USE_DEPRECATED=0 is not used. libstdc++-v3/ChangeLog: PR libstdc++/120187 * include/c_global/ciso646: Only give deprecated warning for C++20 and later. * include/c_global/ccomplex: Add @since to Doxygen comment. * include/c_global/cstdalign: Likewise. * include/c_global/cstdbool: Likewise. * include/c_global/ctgmath: Likewise. * testsuite/18_support/headers/ciso646/macros.cc: Remove dg-warning for c++17_only effective target. * testsuite/18_support/headers/ciso646/macros-2.cc: New test. Reviewed-by: Tomasz Kamiński --- diff --git a/libstdc++-v3/include/c_global/ccomplex b/libstdc++-v3/include/c_global/ccomplex index 7044cf74f6c7..a39273f4a8a2 100644 --- a/libstdc++-v3/include/c_global/ccomplex +++ b/libstdc++-v3/include/c_global/ccomplex @@ -24,6 +24,8 @@ /** @file include/ccomplex * This is a Standard C++ Library header. + * + * @since C++11 (removed in C++20) */ #ifndef _GLIBCXX_CCOMPLEX diff --git a/libstdc++-v3/include/c_global/ciso646 b/libstdc++-v3/include/c_global/ciso646 index a663e04caf08..6dec7df1631f 100644 --- a/libstdc++-v3/include/c_global/ciso646 +++ b/libstdc++-v3/include/c_global/ciso646 @@ -28,6 +28,8 @@ * * This is the C++ version of the Standard C Library header @c iso646.h, * which is empty in C++. + * + * @since C++11 (removed in C++20) */ #ifndef _GLIBCXX_CISO646 #define _GLIBCXX_CISO646 @@ -38,13 +40,15 @@ #include -#if __cplusplus >= 202002L && ! _GLIBCXX_USE_DEPRECATED -# error " is not a standard header in C++20, use to detect implementation-specific macros" -#elif __cplusplus >= 201703L && defined __DEPRECATED -# pragma GCC diagnostic push -# pragma GCC diagnostic ignored "-Wc++23-extensions" -# warning " is deprecated in C++17, use to detect implementation-specific macros" -# pragma GCC diagnostic pop +#if __cplusplus >= 202002L +# if ! _GLIBCXX_USE_DEPRECATED +# error " is not a standard header since C++20, use to detect implementation-specific macros" +# elif defined __DEPRECATED +# pragma GCC diagnostic push +# pragma GCC diagnostic ignored "-Wc++23-extensions" +# warning " is not a standard header since C++20, use to detect implementation-specific macros" +# pragma GCC diagnostic pop +# endif #endif #endif diff --git a/libstdc++-v3/include/c_global/cstdalign b/libstdc++-v3/include/c_global/cstdalign index 92e0ad633089..41ce5065ca08 100644 --- a/libstdc++-v3/include/c_global/cstdalign +++ b/libstdc++-v3/include/c_global/cstdalign @@ -24,6 +24,8 @@ /** @file include/cstdalign * This is a Standard C++ Library header. + * + * @since C++11 (removed in C++20) */ #ifndef _GLIBCXX_CSTDALIGN diff --git a/libstdc++-v3/include/c_global/cstdbool b/libstdc++-v3/include/c_global/cstdbool index e75f56cd5a12..5933d7d96945 100644 --- a/libstdc++-v3/include/c_global/cstdbool +++ b/libstdc++-v3/include/c_global/cstdbool @@ -24,6 +24,8 @@ /** @file include/cstdbool * This is a Standard C++ Library header. + * + * @since C++11 (removed in C++20) */ #ifndef _GLIBCXX_CSTDBOOL diff --git a/libstdc++-v3/include/c_global/ctgmath b/libstdc++-v3/include/c_global/ctgmath index 0a5a0e79b297..b708878ef127 100644 --- a/libstdc++-v3/include/c_global/ctgmath +++ b/libstdc++-v3/include/c_global/ctgmath @@ -24,6 +24,8 @@ /** @file include/ctgmath * This is a Standard C++ Library header. + * + * @since C++11 (removed in C++20) */ #ifndef _GLIBCXX_CTGMATH diff --git a/libstdc++-v3/testsuite/18_support/headers/ciso646/macros-2.cc b/libstdc++-v3/testsuite/18_support/headers/ciso646/macros-2.cc new file mode 100644 index 000000000000..a49292408a33 --- /dev/null +++ b/libstdc++-v3/testsuite/18_support/headers/ciso646/macros-2.cc @@ -0,0 +1,7 @@ +// { dg-options " -Wdeprecated -fno-operator-names" } +// { dg-do preprocess } + +// Should get a warning for C++20 and up without -D_GLIBCXX_USE_DEPRECATED=0 +// { dg-warning "not a standard header" "" { target c++20 } 0 } + +#include "macros.cc" diff --git a/libstdc++-v3/testsuite/18_support/headers/ciso646/macros.cc b/libstdc++-v3/testsuite/18_support/headers/ciso646/macros.cc index ab3a041de062..0cb5168d5ec9 100644 --- a/libstdc++-v3/testsuite/18_support/headers/ciso646/macros.cc +++ b/libstdc++-v3/testsuite/18_support/headers/ciso646/macros.cc @@ -3,7 +3,6 @@ #include -// { dg-warning "deprecated" "" { target c++17_only } 0 } // { dg-error "not a standard header" "" { target c++20 } 0 } #ifdef and