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libstdc++: Fix macro redefinition warnings

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Including <version> after <iterator> gives a warning about redefining
the __cpp_lib_array_constexpr macro. What happens is that <iterator>
sets the C++20 value, then <version> redefines it to the C++17 value,
then undefines it and defines it again to the C++20 value.

This change avoids defining it to the C++17 value when compiling C++20
or later (which also means we no longer need the #undef).

A similar warning happens for __cpp_lib_constexpr_char_traits when
including <version> after any header that includes <bits/char_traits.h>.

libstdc++-v3/ChangeLog:

	* include/std/version (__cpp_lib_array_constexpr):
	(__cpp_lib_constexpr_char_traits): Only define C++17 value when
	compiling C++17.
This commit is contained in:
Jonathan Wakely 2020-09-10 18:51:24 +01:00
parent 0943b55817
commit f903c13ce8
1 changed files with 6 additions and 4 deletions
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10
libstdc++-v3/include/std/version
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@ -122,12 +122,16 @@
#if _GLIBCXX_HOSTED
#define __cpp_lib_any 201606L
#define __cpp_lib_apply 201603
#define __cpp_lib_array_constexpr 201803L
#if __cplusplus == 201703L // N.B. updated value in C++20
# define __cpp_lib_array_constexpr 201803L
#endif
#define __cpp_lib_as_const 201510
#define __cpp_lib_boyer_moore_searcher 201603
#define __cpp_lib_chrono 201611
#define __cpp_lib_clamp 201603
#define __cpp_lib_constexpr_char_traits 201611L
#if __cplusplus == 201703L // N.B. updated value in C++20
# define __cpp_lib_constexpr_char_traits 201611L
#endif
#define __cpp_lib_enable_shared_from_this 201603
#define __cpp_lib_execution 201902L // FIXME: should be 201603L
#define __cpp_lib_filesystem 201703
@ -191,8 +195,6 @@
#define __cpp_lib_unwrap_ref 201811L
#if _GLIBCXX_HOSTED
#undef __cpp_lib_array_constexpr
#undef __cpp_lib_constexpr_char_traits
#define __cpp_lib_array_constexpr 201811L
#define __cpp_lib_assume_aligned 201811L
#define __cpp_lib_bind_front 201907L