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.
Tested powerpc64le-linux. Committed to trunk.
commit f903c13ce8674c623f176eaf4516505205fefcf6
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Thu Sep 10 18:51:24 2020
libstdc++: Fix macro redefinition warnings
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.
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index f64aff4f520..d5d42ed0a72 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -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
