[gcc r13-8157] libstdc++: Fix %S format of duration with floating-point rep

[gcc r13-8157] libstdc++: Fix %S format of duration with floating-point rep

[Jonathan Wakely]

https://gcc.gnu.org/g:354d684ee933e9638206d62e37204f6e63515125

commit r13-8157-g354d684ee933e9638206d62e37204f6e63515125
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Dec 14 15:26:42 2023 +0000

    libstdc++: Fix %S format of duration with floating-point rep
    
    I got the order of arguments to std::format_to wrong. It was in a
    discarded statement, for a case which wasn't being tested.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/chrono_io.h (__formatter_chrono::_M_S): Fix order
            of arguments to std::format_to.
            * testsuite/20_util/duration/io.cc: Test subsecond duration with
            floating-point rep.
    
    (cherry picked from commit 2ef5200a6fb7311074904a1b4bf7ce750618a068)

Diff:
---
 libstdc++-v3/include/bits/chrono_io.h         | 2 +-
 libstdc++-v3/testsuite/20_util/duration/io.cc | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index c94adff3cec..99cacc97fae 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -1159,7 +1159,7 @@ namespace __format
 	      using rep = typename decltype(__ss)::rep;
 	      if constexpr (is_floating_point_v<rep>)
 		{
-		  __out = std::format_to(__loc, std::move(__out),
+		  __out = std::format_to(std::move(__out), __loc,
 					 _GLIBCXX_WIDEN("{:.{}Lg}"),
 					 __ss.count(),
 					 __hms.fractional_width);
diff --git a/libstdc++-v3/testsuite/20_util/duration/io.cc b/libstdc++-v3/testsuite/20_util/duration/io.cc
index 034167c6192..5f0f25eac69 100644
--- a/libstdc++-v3/testsuite/20_util/duration/io.cc
+++ b/libstdc++-v3/testsuite/20_util/duration/io.cc
@@ -96,6 +96,10 @@ test_format()
 		    "required by the chrono-specs") != s.npos);
     }
   }
+
+  std::chrono::duration<float, std::milli> d{0.5};
+  s = std::format("{}", d);
+  VERIFY( s == "0.5ms" );
 }
 
 int main()