[gcc r14-3323] libstdc++: Replace non-type-dependent uses of wchar_t in <format> and <chrono>

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

https://gcc.gnu.org/g:6fabf8f25772bf7a7ff68a31a315cd91b86a186e

commit r14-3323-g6fabf8f25772bf7a7ff68a31a315cd91b86a186e
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Aug 18 11:28:32 2023 +0100

    libstdc++: Replace non-type-dependent uses of wchar_t in <format> and <chrono>
    
    This is one more piece of the rework to make wchar_t support in
    std::format depend on _GLIBCXX_USE_WCHAR_T.
    
    In <format> the __to_wstring_numeric function is called with arguments
    that aren't type-dependent, so a declaration needs to be available, or
    the calls need to be guarded by _GLIBCXX_USE_WCHAR_T.
    
    In <chrono> there is a similarly non-type-dependent call to std::format
    with a wchar_t format string, which is ill-formed when the wchar_t
    overloads of std::format are not declared. Use _GLIBCXX_WIDEN to make it
    type-dependent.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/chrono_io.h (operator<<): Make uses of wide
            strings with streams and std::format type-dependent on _CharT.
            * include/std/format [!_GLIBCXX_USE_WCHAR_T] Do not use
            __to_wstring_numeric.

Diff:
---
 libstdc++-v3/include/bits/chrono_io.h | 17 ++++++-----------
 libstdc++-v3/include/std/format       | 10 ++++++++--
 2 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index e16302baf848..d558802e7d86 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -2390,15 +2390,14 @@ namespace __detail
       __os2.imbue(__os.getloc());
       __os2 << __wdi.weekday();
       const auto __i = __wdi.index();
-      if constexpr (is_same_v<_CharT, char>)
-	__os2 << std::format("[{}", __i);
-      else
-	__os2 << std::format(L"[{}", __i);
-      basic_string_view<_CharT> __s = _GLIBCXX_WIDEN(" is not a valid index]");
+      basic_string_view<_CharT> __s
+	= _GLIBCXX_WIDEN("[ is not a valid index]");
+      __os2 << __s[0];
+      __os2 << std::format(_GLIBCXX_WIDEN("{}"), __i);
       if (__i >= 1 && __i <= 5)
 	__os2 << __s.back();
       else
-	__os2 << __s;
+	__os2 << __s.substr(1);
       __os << __os2.view();
       return __os;
     }
@@ -2457,11 +2456,7 @@ namespace __detail
       // As above, just write straight to a stringstream, as if by "{:L}/last"
       basic_stringstream<_CharT> __os2;
       __os2.imbue(__os.getloc());
-      __os2 << __mdl.month();
-      if constexpr (is_same_v<_CharT, char>)
-	__os2 << "/last";
-      else
-	__os2 << L"/last";
+      __os2 << __mdl.month() << _GLIBCXX_WIDEN("/last");
       __os << __os2.view();
       return __os;
     }
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 0b1ae8201af4..648f847ad969 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -1142,13 +1142,15 @@ namespace __format
 	  basic_string_view<_CharT> __str;
 	  if constexpr (is_same_v<char, _CharT>)
 	    __str = __narrow_str;
+#ifdef _GLIBCXX_USE_WCHAR_T
 	  else
 	    {
 	      size_t __n = __narrow_str.size();
 	      auto __p = (_CharT*)__builtin_alloca(__n * sizeof(_CharT));
-	      __to_wstring_numeric(__narrow_str.data(), __n, __p);
+	      std::__to_wstring_numeric(__narrow_str.data(), __n, __p);
 	      __str = {__p, __n};
 	    }
+#endif
 
 	  if (_M_spec._M_localized)
 	    {
@@ -1624,11 +1626,13 @@ namespace __format
 	  basic_string_view<_CharT> __str;
 	  if constexpr (is_same_v<_CharT, char>)
 	    __str = __narrow_str;
+#ifdef _GLIBCXX_USE_WCHAR_T
 	  else
 	    {
 	      __wstr = std::__to_wstring_numeric(__narrow_str);
 	      __str = __wstr;
 	    }
+#endif
 
 	  if (_M_spec._M_localized)
 	    {
@@ -2290,12 +2294,14 @@ namespace __format
 	  basic_string_view<_CharT> __str;
 	  if constexpr (is_same_v<_CharT, char>)
 	    __str = string_view(__buf, __n);
+#ifdef _GLIBCXX_USE_WCHAR_T
 	  else
 	    {
 	      auto __p = (_CharT*)__builtin_alloca(__n * sizeof(_CharT));
-	      __to_wstring_numeric(__buf, __n, __p);
+	      std::__to_wstring_numeric(__buf, __n, __p);
 	      __str = wstring_view(__p, __n);
 	    }
+#endif
 
 #if _GLIBCXX_P2518R3
 	  if (_M_spec._M_zero_fill)