[committed] libstdc++: Define __cpp_lib_to_chars for C++20 [PR 100146]

[Jonathan Wakely <jwakely@redhat.com>]

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This defines the feature test macro when uselocale is available, because
the floating-point std::from_chars support currently depends on that.

Co-authored-by: Jakub Jelinek <jakub@redhat.com>

libstdc++-v3/ChangeLog:

	PR libstdc++/100146
	* include/std/charconv (__cpp_lib_to_chars): Define
	conditionally.
	* include/std/version (__cpp_lib_to_chars): Likewise..
	* testsuite/20_util/from_chars/4.cc: Only check feature test
	macro, not _GLIBCXX_HAVE_USELOCALE.
	* testsuite/20_util/from_chars/5.cc: Likewise.
	* testsuite/20_util/from_chars/6.cc: Likewise.
	* testsuite/20_util/to_chars/long_double.cc: Likewise.

Tested x86_64-linux. Committed to trunk. I'll also backport to gcc-11.



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commit f1a68574b1f8d2961d3a676dbcf0cc24b6368578
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Apr 20 12:46:11 2021

    libstdc++: Define __cpp_lib_to_chars for C++20 [PR 100146]
    
    This defines the feature test macro when uselocale is available, because
    the floating-point std::from_chars support currently depends on that.
    
    Co-authored-by: Jakub Jelinek <jakub@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/100146
            * include/std/charconv (__cpp_lib_to_chars): Define
            conditionally.
            * include/std/version (__cpp_lib_to_chars): Likewise..
            * testsuite/20_util/from_chars/4.cc: Only check feature test
            macro, not _GLIBCXX_HAVE_USELOCALE.
            * testsuite/20_util/from_chars/5.cc: Likewise.
            * testsuite/20_util/from_chars/6.cc: Likewise.
            * testsuite/20_util/to_chars/long_double.cc: Likewise.

diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index 851b1e5cac2..6e407f31e30 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -44,8 +44,9 @@
 #include <bits/error_constants.h> // for std::errc
 #include <ext/numeric_traits.h>
 
-// FIXME: Define when floating point is supported:
-// #define __cpp_lib_to_chars 201611L
+#if _GLIBCXX_HAVE_USELOCALE
+# define __cpp_lib_to_chars 201611L
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index cb25148fca5..d9f6a3c3dfd 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -161,7 +161,9 @@
 #endif
 #define __cpp_lib_shared_ptr_weak_type 201606
 #define __cpp_lib_string_view 201803L
-// #define __cpp_lib_to_chars 201611L
+#if _GLIBCXX_HAVE_USELOCALE
+# define __cpp_lib_to_chars 201611L
+#endif
 #define __cpp_lib_unordered_map_try_emplace 201411
 #define __cpp_lib_variant 201606L
 #endif
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/4.cc b/libstdc++-v3/testsuite/20_util/from_chars/4.cc
index 1482b5dfb6e..7cee4dcbc23 100644
--- a/libstdc++-v3/testsuite/20_util/from_chars/4.cc
+++ b/libstdc++-v3/testsuite/20_util/from_chars/4.cc
@@ -28,9 +28,7 @@
 
 // Test std::from_chars floating-point conversions.
 
-// As of July 2020 __cpp_lib_to_chars is not defined, but std::from_chars
-// works for floating-point types when _GLIBCXX_HAVE_USELOCALE is defined.
-#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
+#if __cpp_lib_to_chars >= 201611L
 void
 test01()
 {
@@ -363,7 +361,7 @@ test06()
 int
 main()
 {
-#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
+#if __cpp_lib_to_chars >= 201611L
   test01();
   test02();
   test03();
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/5.cc b/libstdc++-v3/testsuite/20_util/from_chars/5.cc
index dd5f9229f68..fa86ab7383c 100644
--- a/libstdc++-v3/testsuite/20_util/from_chars/5.cc
+++ b/libstdc++-v3/testsuite/20_util/from_chars/5.cc
@@ -25,9 +25,7 @@
 
 // Test std::from_chars error handling.
 
-// As of July 2020 __cpp_lib_to_chars is not defined, but std::from_chars
-// works for floating-point types when _GLIBCXX_HAVE_USELOCALE is defined.
-#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
+#if __cpp_lib_to_chars >= 201611L
 void
 test01()
 {
@@ -160,7 +158,7 @@ test04()
 int
 main()
 {
-#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
+#if __cpp_lib_to_chars >= 201611L
   test01();
   test02();
   test03();
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/6.cc b/libstdc++-v3/testsuite/20_util/from_chars/6.cc
index 58e0f1fc932..139a1811db0 100644
--- a/libstdc++-v3/testsuite/20_util/from_chars/6.cc
+++ b/libstdc++-v3/testsuite/20_util/from_chars/6.cc
@@ -27,7 +27,7 @@
 void
 test01()
 {
-#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
+#if __cpp_lib_to_chars >= 201611L
 #if _GLIBCXX_USE_C99_FENV_TR1
   double d;
   std::fesetround(FE_DOWNWARD);
diff --git a/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc b/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc
index 22d42067d65..8cf45ad5e94 100644
--- a/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc
+++ b/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc
@@ -69,7 +69,7 @@ test01()
   // Verifies correctness of the hexadecimal form [BEGIN,END) for VALUE by
   // round-tripping it through from_chars (if available).
   auto verify_via_from_chars = [] (char *begin, char *end, long double value) {
-#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
+#if __cpp_lib_to_chars >= 201611L
     long double roundtrip;
     auto result = from_chars(begin, end, roundtrip, chars_format::hex);
     VERIFY( result.ec == errc{} );