[PATCH] libstdc++: Fix constification in range_formatter::format v2 [PR109162]

[Tomasz Kamiński]

Because the _M_format(__rg, __fc) were placed outside of if constexpr,
these method and it's childs where instantiated, even if _M_format<const _Range>
could be used. Now we put the calls in else branch of if constexpr.

libstdc++-v3/ChangeLog:

        * include/std/format (range_formatter::format): Do not instantiate
        _M_format for mutable _Rg if const _Rg can be used.
---
Testing on x86_64-linux, but there are no tests that will detect
uncessary instantiations.

 libstdc++-v3/include/std/format | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 27253f50ea8..d44c4b24abe 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -5636,12 +5636,15 @@ namespace __format
        {
          using _Range = remove_reference_t<_Rg>;
          if constexpr (__format::__const_formattable_range<_Range, _CharT>)
-         {
-           using _CRef = ranges::range_reference_t<const _Range>;
-           if constexpr (same_as<remove_cvref_t<_CRef>, _Tp>)
-             return _M_format<const _Range>(__rg, __fc);
-         }
-         return _M_format(__rg, __fc);
+           {
+             using _CRef = ranges::range_reference_t<const _Range>;
+             if constexpr (same_as<remove_cvref_t<_CRef>, _Tp>)
+               return _M_format<const _Range>(__rg, __fc);
+             else
+               return _M_format(__rg, __fc);
+           }
+         else
+           return _M_format(__rg, __fc);
        }
 
     private:
-- 
2.49.0