[gcc r15-5] libstdc++: Do not apply localized formatting to NaN and inf [PR114863]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:a0bc71e480132a528a4869c1cd7863f709768c53

commit r15-5-ga0bc71e480132a528a4869c1cd7863f709768c53
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Apr 26 11:42:26 2024 +0100

    libstdc++: Do not apply localized formatting to NaN and inf [PR114863]
    
    We don't want to add grouping to strings like "-inf", and there is no
    radix character to replace either.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/114863
            * include/std/format (__formatter_fp::format): Only use
            _M_localized for finite values.
            * testsuite/std/format/functions/format.cc: Check localized
            formatting of NaN and initiny.

Diff:
---
 libstdc++-v3/include/std/format                       | 2 +-
 libstdc++-v3/testsuite/std/format/functions/format.cc | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 22dcb5f24bd..48deba2bcb2 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -1734,7 +1734,7 @@ namespace __format
 	    }
 #endif
 
-	  if (_M_spec._M_localized)
+	  if (_M_spec._M_localized && __builtin_isfinite(__v))
 	    {
 	      __wstr = _M_localize(__str, __expc, __fc.locale());
 	      if (!__wstr.empty())
diff --git a/libstdc++-v3/testsuite/std/format/functions/format.cc b/libstdc++-v3/testsuite/std/format/functions/format.cc
index 4499397aaf9..78cc1ab482a 100644
--- a/libstdc++-v3/testsuite/std/format/functions/format.cc
+++ b/libstdc++-v3/testsuite/std/format/functions/format.cc
@@ -248,6 +248,14 @@ test_locale()
   s = std::format(cloc, "{:05L}", -1.0); // PR libstdc++/110968
   VERIFY( s == "-0001" );
 
+  // PR libstdc++/114863 grouping applied to nan and inf
+  double inf = std::numeric_limits<double>::infinity();
+  s = std::format(eloc, "{0:Le} {0:Lf} {0:Lg}", -inf);
+  VERIFY( s == "-inf -inf -inf" );
+  double nan = std::numeric_limits<double>::quiet_NaN();
+  s = std::format(eloc, "{0:Le} {0:Lf} {0:Lg}", -nan);
+  VERIFY( s == "-nan -nan -nan" );
+
   // Restore
   std::locale::global(cloc);
 }