[committed,1/2] libstdc++: Implement P2905R2 "Runtime format strings" for C++20

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index c30451651ea..ec2ae9d53cc 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -2273,7 +2273,8 @@  namespace __detail
       _Str __s = _GLIBCXX_WIDEN("{:02d} is not a valid day");
       if (__d.ok())
 	__s = __s.substr(0, 6);
-      __os << std::vformat(__s, make_format_args<_Ctx>((unsigned)__d));
+      auto __u = (unsigned)__d;
+      __os << std::vformat(__s, make_format_args<_Ctx>(__u));
       return __os;
     }
 
@@ -2302,8 +2303,10 @@  namespace __detail
 	__os << std::vformat(__os.getloc(), __s.substr(0, 6),
 			     make_format_args<_Ctx>(__m));
       else
-	__os << std::vformat(__s.substr(6),
-			     make_format_args<_Ctx>((unsigned)__m));
+	{
+	  auto __u = (unsigned)__m;
+	  __os << std::vformat(__s.substr(6), make_format_args<_Ctx>(__u));
+	}
       return __os;
     }
 
@@ -2364,8 +2367,10 @@  namespace __detail
 	__os << std::vformat(__os.getloc(), __s.substr(0, 6),
 			     make_format_args<_Ctx>(__wd));
       else
-	__os << std::vformat(__s.substr(6),
-			     make_format_args<_Ctx>(__wd.c_encoding()));
+	{
+	  auto __c = __wd.c_encoding();
+	  __os << std::vformat(__s.substr(6), make_format_args<_Ctx>(__c));
+	}
       return __os;
     }
 
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 0d9f70ee555..160efa5155c 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -3413,7 +3413,7 @@  namespace __format
 
       template<typename _Ctx, typename... _Argz>
 	friend auto
-	make_format_args(_Argz&&...) noexcept;
+	make_format_args(_Argz&...) noexcept;
 
       template<typename _Visitor, typename _Ctx>
 	friend decltype(auto)
@@ -3583,7 +3583,7 @@  namespace __format
 
       template<typename _Ctx, typename... _Args>
 	friend auto
-	make_format_args(_Args&&...) noexcept;
+	make_format_args(_Args&...) noexcept;
 
       // An array of _Arg_t enums corresponding to _Args...
       template<typename... _Args>
@@ -3621,7 +3621,7 @@  namespace __format
 
   template<typename _Context, typename... _Args>
     auto
-    make_format_args(_Args&&... __fmt_args) noexcept;
+    make_format_args(_Args&... __fmt_args) noexcept;
 
   // An array of type-erased formatting arguments.
   template<typename _Context, typename... _Args>
@@ -3637,7 +3637,7 @@  namespace __format
 #else
 	std::
 #endif
-	make_format_args(_Argz&&...) noexcept;
+	make_format_args(_Argz&...) noexcept;
 
       // For a sufficiently small number of arguments we only store values.
       // basic_format_args can get the types from the _Args pack.
@@ -3711,11 +3711,11 @@  namespace __format
   template<typename _Context = format_context, typename... _Args>
     [[nodiscard,__gnu__::__always_inline__]]
     inline auto
-    make_format_args(_Args&&... __fmt_args) noexcept
+    make_format_args(_Args&... __fmt_args) noexcept
     {
       using _Fmt_arg = basic_format_arg<_Context>;
       using _Store = __format::_Arg_store<_Context, typename _Fmt_arg::template
-		     _Normalize<remove_reference_t<_Args>>...>;
+		     _Normalize<_Args>...>;
       return _Store(__fmt_args...);
     }
 
@@ -3724,7 +3724,7 @@  namespace __format
   template<typename... _Args>
     [[nodiscard,__gnu__::__always_inline__]]
     inline auto
-    make_wformat_args(_Args&&... __args) noexcept
+    make_wformat_args(_Args&... __args) noexcept
     { return std::make_format_args<wformat_context>(__args...); }
 #endif
 
@@ -4240,7 +4240,7 @@  namespace __format
     format_to(_Out __out, format_string<_Args...> __fmt, _Args&&... __args)
     {
       return std::vformat_to(std::move(__out), __fmt.get(),
-			     std::make_format_args(std::forward<_Args>(__args)...));
+			     std::make_format_args(__args...));
     }
 
 #ifdef _GLIBCXX_USE_WCHAR_T
@@ -4250,7 +4250,7 @@  namespace __format
     format_to(_Out __out, wformat_string<_Args...> __fmt, _Args&&... __args)
     {
       return std::vformat_to(std::move(__out), __fmt.get(),
-			     std::make_wformat_args(std::forward<_Args>(__args)...));
+			     std::make_wformat_args(__args...));
     }
 #endif
 
@@ -4261,7 +4261,7 @@  namespace __format
 	      _Args&&... __args)
     {
       return std::vformat_to(std::move(__out), __loc, __fmt.get(),
-			     std::make_format_args(std::forward<_Args>(__args)...));
+			     std::make_format_args(__args...));
     }
 
 #ifdef _GLIBCXX_USE_WCHAR_T
@@ -4272,7 +4272,7 @@  namespace __format
 	      _Args&&... __args)
     {
       return std::vformat_to(std::move(__out), __loc, __fmt.get(),
-			     std::make_wformat_args(std::forward<_Args>(__args)...));
+			     std::make_wformat_args(__args...));
     }
 #endif
 
@@ -4379,7 +4379,7 @@  namespace __format
     {
       __format::_Counting_sink<char> __buf;
       std::vformat_to(__buf.out(), __fmt.get(),
-		      std::make_format_args(std::forward<_Args>(__args)...));
+		      std::make_format_args(__args...));
       return __buf.count();
     }
 
@@ -4391,7 +4391,7 @@  namespace __format
     {
       __format::_Counting_sink<wchar_t> __buf;
       std::vformat_to(__buf.out(), __fmt.get(),
-		      std::make_wformat_args(std::forward<_Args>(__args)...));
+		      std::make_wformat_args(__args...));
       return __buf.count();
     }
 #endif
@@ -4404,7 +4404,7 @@  namespace __format
     {
       __format::_Counting_sink<char> __buf;
       std::vformat_to(__buf.out(), __loc, __fmt.get(),
-		      std::make_format_args(std::forward<_Args>(__args)...));
+		      std::make_format_args(__args...));
       return __buf.count();
     }
 
@@ -4417,7 +4417,7 @@  namespace __format
     {
       __format::_Counting_sink<wchar_t> __buf;
       std::vformat_to(__buf.out(), __loc, __fmt.get(),
-		      std::make_wformat_args(std::forward<_Args>(__args)...));
+		      std::make_wformat_args(__args...));
       return __buf.count();
     }
 #endif
diff --git a/libstdc++-v3/include/std/ostream b/libstdc++-v3/include/std/ostream
index 4dff0cf645d..7d501d67489 100644
--- a/libstdc++-v3/include/std/ostream
+++ b/libstdc++-v3/include/std/ostream
@@ -981,7 +981,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline void
     print(ostream& __os, format_string<_Args...> __fmt, _Args&&... __args)
     {
-      auto __fmtargs = std::make_format_args(std::forward<_Args>(__args)...);
+      auto __fmtargs = std::make_format_args(__args...);
       if constexpr (__unicode::__literal_encoding_is_utf8())
 	std::vprint_unicode(__os, __fmt.get(), __fmtargs);
       else
diff --git a/libstdc++-v3/include/std/print b/libstdc++-v3/include/std/print
index f44256c5dca..492f333dfa6 100644
--- a/libstdc++-v3/include/std/print
+++ b/libstdc++-v3/include/std/print
@@ -103,7 +103,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline void
     print(FILE* __stream, format_string<_Args...> __fmt, _Args&&... __args)
     {
-      auto __fmtargs = std::make_format_args(std::forward<_Args>(__args)...);
+      auto __fmtargs = std::make_format_args(__args...);
       if constexpr (__unicode::__literal_encoding_is_utf8())
 	std::vprint_unicode(__stream, __fmt.get(), __fmtargs);
       else
diff --git a/libstdc++-v3/testsuite/20_util/duration/io.cc b/libstdc++-v3/testsuite/20_util/duration/io.cc
index 0582c0075a5..e141baf42dc 100644
--- a/libstdc++-v3/testsuite/20_util/duration/io.cc
+++ b/libstdc++-v3/testsuite/20_util/duration/io.cc
@@ -82,7 +82,8 @@  test_format()
     char fmt[] = { '{', ':', '%', c, '}' };
     try
     {
-      (void) std::vformat(std::string_view(fmt, 5), std::make_format_args(1s));
+      auto s = 1s;
+      (void) std::vformat(std::string_view(fmt, 5), std::make_format_args(s));
       // The call above should throw for any conversion-spec not in my_specs:
       VERIFY(my_specs.find(c) != my_specs.npos);
     }
diff --git a/libstdc++-v3/testsuite/std/format/arguments/args.cc b/libstdc++-v3/testsuite/std/format/arguments/args.cc
index a45f3fb24df..eba129ff894 100644
--- a/libstdc++-v3/testsuite/std/format/arguments/args.cc
+++ b/libstdc++-v3/testsuite/std/format/arguments/args.cc
@@ -46,7 +46,12 @@  struct std::formatter<E> : std::formatter<int>
 void
 test_args()
 {
-  auto store = std::make_format_args(false, 1, '2', 3.4);
+  bool b = false;
+  int i = 1;
+  char c = '2';
+  double d = 3.4;
+
+  auto store = std::make_format_args(b, i, c, d);
   std::format_args args = store;
   VERIFY(equals(args.get(0), false));
   VERIFY(equals(args.get(1), 1));
@@ -54,7 +59,11 @@  test_args()
   VERIFY(equals(args.get(3), 3.4));
   VERIFY(!args.get(4));
 
-  auto cstore = std::make_format_args<std::format_context>(5L, 6ULL, 7.8f);
+  long l = 5L;
+  unsigned long long ull = 6ULL;
+  float f = 7.8f;
+
+  auto cstore = std::make_format_args<std::format_context>(l, ull, f);
   std::format_args cargs = cstore;
   if constexpr (sizeof(long) == sizeof(int))
     VERIFY(equals(cargs.get(0), 5));
@@ -64,14 +73,17 @@  test_args()
   VERIFY(equals(cargs.get(2), 7.8f));
   VERIFY(!cargs.get(3));
 
-  VERIFY(equals(std::format_args(std::make_format_args(std::string("tenfour"))).get(0), std::string_view("tenfour")));
+  std::string s = "tenfour";
+  VERIFY(equals(std::format_args(std::make_format_args(s)).get(0), std::string_view("tenfour")));
 
+  char nine = '9';
+  wchar_t ten = L'X';
   // This needs to be on the stack so that testing pointer equality works.
   wchar_t eleven[] = L"eleven";
-  // This needs to be on the stack so that the wstring_view doesn't dangle.
+  long double twelve13 = 12.13L;
   std::wstring tenfour = L"tenfour";
 
-  auto wstore = std::make_wformat_args('9', L'X', eleven, 12.13L, tenfour);
+  auto wstore = std::make_wformat_args(nine, ten, eleven, twelve13, tenfour);
   std::wformat_args wargs = wstore;
   VERIFY(equals(wargs.get(0), static_cast<wchar_t>('9')));
   VERIFY(equals(wargs.get(1), L'X'));
@@ -80,7 +92,9 @@  test_args()
   VERIFY(equals(wargs.get(4), std::wstring_view(tenfour)));
   VERIFY(!wargs.get(5));
 
-  auto another_store = std::make_format_args(nullptr, E::ByGum);
+  std::nullptr_t null;
+  E eebygum = E::ByGum;
+  auto another_store = std::make_format_args(null, eebygum);
   args = another_store;
   VERIFY(equals(args.get(0), static_cast<const void*>(nullptr)));
   using handle = std::basic_format_arg<std::format_context>::handle;
diff --git a/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc
new file mode 100644
index 00000000000..16ac3040146
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc
@@ -0,0 +1,12 @@ 
+// { dg-do compile { target c++20 } }
+
+// P2905R2 Runtime format strings
+
+#include <format>
+
+std::string rval() { return "path/etic/experience"; }
+
+void f()
+{
+  (void)std::make_format_args(rval()); // { dg-error "cannot bind non-const lvalue reference" }
+}
diff --git a/libstdc++-v3/testsuite/std/format/arguments/lwg3810.cc b/libstdc++-v3/testsuite/std/format/arguments/lwg3810.cc
index f89f40203cb..8a9f9edd578 100644
--- a/libstdc++-v3/testsuite/std/format/arguments/lwg3810.cc
+++ b/libstdc++-v3/testsuite/std/format/arguments/lwg3810.cc
@@ -4,7 +4,11 @@ 
 
 #include <format>
 
-auto args_store = std::make_format_args(1,2,3);
+int x = 1;
+long y = 2;
+short z = 3;
+
+auto args_store = std::make_format_args(x, y, z);
 std::basic_format_args args = args_store;
 static_assert(std::is_same_v<decltype(args), std::format_args>);
 
@@ -20,5 +24,5 @@  test_ctad()
   using SomeContext = std::wformat_context;
 
   // foo(make_format_args<SomeContext>(...)); // won't work
-  foo(basic_format_args(make_format_args<SomeContext>(1, 2, 3))); // should work
+  foo(basic_format_args(make_format_args<SomeContext>(x, y, z))); // should work
 }
diff --git a/libstdc++-v3/testsuite/std/format/functions/format.cc b/libstdc++-v3/testsuite/std/format/functions/format.cc
index 6320e20170c..63702edbd42 100644
--- a/libstdc++-v3/testsuite/std/format/functions/format.cc
+++ b/libstdc++-v3/testsuite/std/format/functions/format.cc
@@ -267,14 +267,16 @@  test_width()
   }
 
   try {
-    auto args = std::make_format_args(false, true);
+    bool no = false, yes = true;
+    auto args = std::make_format_args(no, yes);
     s = std::vformat("DR 3720: restrict type of width arg-id {0:{1}}", args);
     VERIFY(false);
   } catch (const std::format_error&) {
   }
 
   try {
-    auto args = std::make_format_args('?', '!');
+    char wat = '?', bang = '!';
+    auto args = std::make_format_args(wat, bang);
     s = std::vformat("DR 3720: restrict type of width arg-id {0:{1}}", args);
     VERIFY(false);
   } catch (const std::format_error&) {
diff --git a/libstdc++-v3/testsuite/std/format/functions/vformat_to.cc b/libstdc++-v3/testsuite/std/format/functions/vformat_to.cc
index fe0367f7496..2be3d6f6761 100644
--- a/libstdc++-v3/testsuite/std/format/functions/vformat_to.cc
+++ b/libstdc++-v3/testsuite/std/format/functions/vformat_to.cc
@@ -29,17 +29,22 @@  private:
 void
 test_move_only()
 {
+  const char arg1[] = "matte";
+  int arg2 = '!';
+
   std::string str;
   move_only_iterator<char> mo(std::back_inserter(str));
   auto res = std::vformat_to(std::move(mo), "for{:.3} that{:c}",
-			     std::make_format_args("matte", (int)'!'));
+			     std::make_format_args(arg1, arg2));
   static_assert(std::is_same_v<decltype(res), decltype(mo)>);
   VERIFY( str == "format that!" );
 
+  const wchar_t warg1[] = L"matte";
+  long warg2 = L'!';
   std::wstring wstr;
   move_only_iterator<wchar_t> wmo(std::back_inserter(wstr));
   auto wres = std::vformat_to(std::move(wmo), L"for{:.3} that{:c}",
-			      std::make_wformat_args(L"matte", (long)L'!'));
+			      std::make_wformat_args(warg1, warg2));
   static_assert(std::is_same_v<decltype(wres), decltype(wmo)>);
   VERIFY( wstr == L"format that!" );
 }
diff --git a/libstdc++-v3/testsuite/std/format/string.cc b/libstdc++-v3/testsuite/std/format/string.cc
index 40aaebae04e..ddb3c5625cd 100644
--- a/libstdc++-v3/testsuite/std/format/string.cc
+++ b/libstdc++-v3/testsuite/std/format/string.cc
@@ -149,8 +149,9 @@  void
 test_pr110862()
 {
   try {
+    int i = 1;
     // PR libstdc++/110862 out-of-bounds read on invalid format string
-    (void) std::vformat("{0:{0}", std::make_format_args(1));
+    (void) std::vformat("{0:{0}", std::make_format_args(i));
     VERIFY( false );
   } catch (const std::format_error& e) {
     std::string_view what = e.what();
@@ -162,9 +163,11 @@  void
 test_pr110974()
 {
   try {
+    double d = 1.0;
+    int i = 1;
     // PR libstdc++/110974 out of bounds read on invalid format string "{:{}."
     std::string_view fmt{"{:{}.0", 5}; // "0" is not part of the format string.
-    (void) std::vformat(fmt, std::make_format_args(1.0, 1));
+    (void) std::vformat(fmt, std::make_format_args(d, i));
     VERIFY( false );
   } catch (const std::format_error& e) {
     std::string_view what = e.what();
diff --git a/libstdc++-v3/testsuite/std/time/day/io.cc b/libstdc++-v3/testsuite/std/time/day/io.cc
index 3454657f69f..36ce7ec7d17 100644
--- a/libstdc++-v3/testsuite/std/time/day/io.cc
+++ b/libstdc++-v3/testsuite/std/time/day/io.cc
@@ -51,8 +51,8 @@  test_format()
     char fmt[] = { '{', ':', '%', c, '}' };
     try
     {
-      (void) std::vformat(std::string_view(fmt, 5),
-			  std::make_format_args(day(1)));
+      day d(1);
+      (void) std::vformat(std::string_view(fmt, 5), std::make_format_args(d));
       // The call above should throw for any conversion-spec not in my_specs:
       VERIFY(my_specs.find(c) != my_specs.npos);
     }
diff --git a/libstdc++-v3/testsuite/std/time/month/io.cc b/libstdc++-v3/testsuite/std/time/month/io.cc
index 7e80a53bbb6..99ec0737305 100644
--- a/libstdc++-v3/testsuite/std/time/month/io.cc
+++ b/libstdc++-v3/testsuite/std/time/month/io.cc
@@ -74,8 +74,8 @@  test_format()
     char fmt[] = { '{', ':', '%', c, '}' };
     try
     {
-      (void) std::vformat(std::string_view(fmt, 5),
-			  std::make_format_args(month(1)));
+      month m(1);
+      (void) std::vformat(std::string_view(fmt, 5), std::make_format_args(m));
       // The call above should throw for any conversion-spec not in my_specs:
       VERIFY(my_specs.find(c) != my_specs.npos);
     }
diff --git a/libstdc++-v3/testsuite/std/time/weekday/io.cc b/libstdc++-v3/testsuite/std/time/weekday/io.cc
index 5ed90282f95..a56cdaef88c 100644
--- a/libstdc++-v3/testsuite/std/time/weekday/io.cc
+++ b/libstdc++-v3/testsuite/std/time/weekday/io.cc
@@ -77,8 +77,8 @@  test_format()
     char fmt[] = { '{', ':', '%', c, '}' };
     try
     {
-      (void) std::vformat(std::string_view(fmt, 5),
-			  std::make_format_args(weekday(1)));
+      weekday wd(1);
+      (void) std::vformat(std::string_view(fmt, 5), std::make_format_args(wd));
       // The call above should throw for any conversion-spec not in my_specs:
       VERIFY(my_specs.find(c) != my_specs.npos);
     }
diff --git a/libstdc++-v3/testsuite/std/time/year/io.cc b/libstdc++-v3/testsuite/std/time/year/io.cc
index a6683ae20df..bcaa57faeb7 100644
--- a/libstdc++-v3/testsuite/std/time/year/io.cc
+++ b/libstdc++-v3/testsuite/std/time/year/io.cc
@@ -68,8 +68,8 @@  test_format()
     char fmt[] = { '{', ':', '%', c, '}' };
     try
     {
-      (void) std::vformat(std::string_view(fmt, 5),
-			  std::make_format_args(year(2022)));
+      year y = 2022y;
+      (void) std::vformat(std::string_view(fmt, 5), std::make_format_args(y));
       // The call above should throw for any conversion-spec not in my_specs:
       VERIFY(my_specs.find(c) != my_specs.npos);
     }
diff --git a/libstdc++-v3/testsuite/std/time/year_month_day/io.cc b/libstdc++-v3/testsuite/std/time/year_month_day/io.cc
index 15c5a9f77be..cb82ef3b612 100644
--- a/libstdc++-v3/testsuite/std/time/year_month_day/io.cc
+++ b/libstdc++-v3/testsuite/std/time/year_month_day/io.cc
@@ -97,8 +97,8 @@  test_format()
     char fmt[] = { '{', ':', '%', c, '}' };
     try
     {
-      (void) std::vformat(std::string_view(fmt, 5),
-			  std::make_format_args(2022y/December/19));
+      year_month_day ymd = 2022y/December/19;
+      (void) std::vformat(std::string_view(fmt, 5), std::make_format_args(ymd));
       // The call above should throw for any conversion-spec not in my_specs:
       VERIFY(my_specs.find(c) != my_specs.npos);
     }