[libc++][format] Fixes invalid usage of m type.

[Mordante]

Summary

The m type in a range formatter may only be used when a pair or a tuple
with two elements is used. This was not correctly validated as reported
in llvm.org/PR60995.

[ldionne]

Let's cherry-pick this one too.

[Mordante]

Thanks for the review!

In D145309#4175441, @ldionne wrote:

Let's cherry-pick this one too.

Agreed with both of them, that's why I marked them as a bug ;-)

libcxx/include/__format/concepts.h

 concept formattable = __formattable<_Tp, _CharT>;
 
 // [tuple.like] defines a tuple-like exposition only concept. This concept is
 // not related to that. Therefore it uses a different name for the concept.
 //
 // TODO FMT Add a test to validate we fail when using that concept after P2165
 // has been implemented.
 template <class _Tp>
-concept __fmt_pair_like = __is_specialization_v<_Tp, pair> ||
-                          // Use a requires since tuple_size_v may fail to instantiate,
-                          (__is_specialization_v<_Tp, tuple> && requires { tuple_size_v<_Tp> == 2; });
+concept __fmt_pair_like =
+    __is_specialization_v<_Tp, pair> || (__is_specialization_v<_Tp, tuple> && tuple_size_v<_Tp> == 2);
 
 #  endif //_LIBCPP_STD_VER >= 23
 #endif //_LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FORMAT_CONCEPTS_H

libcxx/test/std/utilities/format/format.range/format.range.fmtset/format.functions.tests.h

void test_tuple_int(TestFunction check, ExceptionTest check_exception) {
 
   // *** locale-specific form ***
   check_exception("The format-spec should consume the input or end with a '}'", SV("{:L}"), input);
 
   // *** n
   check(SV("__(42), (99)___"), SV("{:_^15n}"), input);
 
   // *** type ***
-  check(SV("__{(42), (99)}___"), SV("{:_^17m}"), input);
+  check_exception("The range-format-spec type m requires two elements for a pair or tuple", SV("{:m}"), input);
   check_exception("The range-format-spec type s requires formatting a character type", SV("{:s}"), input);
   check_exception("The range-format-spec type ?s requires formatting a character type", SV("{:?s}"), input);
 
   for (std::basic_string_view<CharT> fmt : fmt_invalid_types<CharT>("s"))
     check_exception("The format-spec should consume the input or end with a '}'", fmt, input);
 
   // ***** Only underlying has a format-spec
   check(SV("{(42)   , (99)   }"), SV("{::7}"), input);
void test_tuple_int_int_int(TestFunction check, ExceptionTest check_exception) {
 
   // *** locale-specific form ***
   check_exception("The format-spec should consume the input or end with a '}'", SV("{:L}"), input);
 
   // *** n
   check(SV("__(1, 10, 100), (42, 99, 0)___"), SV("{:_^30n}"), input);
 
   // *** type ***
-  check(SV("__{(1, 10, 100), (42, 99, 0)}___"), SV("{:_^32m}"), input);
+  check_exception("The range-format-spec type m requires two elements for a pair or tuple", SV("{:m}"), input);
   check_exception("The range-format-spec type s requires formatting a character type", SV("{:s}"), input);
   check_exception("The range-format-spec type ?s requires formatting a character type", SV("{:?s}"), input);
 
   for (std::basic_string_view<CharT> fmt : fmt_invalid_types<CharT>("s"))
     check_exception("The format-spec should consume the input or end with a '}'", fmt, input);
 
   // ***** Only underlying has a format-spec
   check(SV("{(1, 10, 100)  , (42, 99, 0)   }"), SV("{::14}"), input);

libcxx/test/std/utilities/format/format.range/format.range.formatter/format.functions.tests.h

void test_tuple_int(TestFunction check, ExceptionTest check_exception) {
 
   // *** locale-specific form ***
   check_exception("The format-spec should consume the input or end with a '}'", SV("{:L}"), input);
 
   // *** n
   check(SV("__(42), (99)___"), SV("{:_^15n}"), input);
 
   // *** type ***
-  check(SV("__{(42), (99)}___"), SV("{:_^17m}"), input);
+  check_exception("The range-format-spec type m requires two elements for a pair or tuple", SV("{:m}"), input);
   check_exception("The range-format-spec type s requires formatting a character type", SV("{:s}"), input);
   check_exception("The range-format-spec type ?s requires formatting a character type", SV("{:?s}"), input);
   for (std::basic_string_view<CharT> fmt : fmt_invalid_types<CharT>("s"))
     check_exception("The format-spec should consume the input or end with a '}'", fmt, input);
 
   // ***** Only underlying has a format-spec
   check(SV("[(42)   , (99)   ]"), SV("{::7}"), input);
   check(SV("[(42)***, (99)***]"), SV("{::*<7}"), input);
void test_tuple_int_int_int(TestFunction check, ExceptionTest check_exception) {
 
   // *** locale-specific form ***
   check_exception("The format-spec should consume the input or end with a '}'", SV("{:L}"), input);
 
   // *** n
   check(SV("__(42, 99, 0), (1, 10, 100)___"), SV("{:_^30n}"), input);
 
   // *** type ***
-  check(SV("__{(42, 99, 0), (1, 10, 100)}___"), SV("{:_^32m}"), input);
+  check_exception("The range-format-spec type m requires two elements for a pair or tuple", SV("{:m}"), input);
   check_exception("The range-format-spec type s requires formatting a character type", SV("{:s}"), input);
   check_exception("The range-format-spec type ?s requires formatting a character type", SV("{:?s}"), input);
   for (std::basic_string_view<CharT> fmt : fmt_invalid_types<CharT>("s"))
     check_exception("The format-spec should consume the input or end with a '}'", fmt, input);
 
   // ***** Only underlying has a format-spec
   check(SV("[(42, 99, 0)   , (1, 10, 100)  ]"), SV("{::14}"), input);
   check(SV("[(42, 99, 0)***, (1, 10, 100)**]"), SV("{::*<14}"), input);