[libc++][format] Fixes escaping string literals.

[Mordante]

Summary

D140653 has the same fix, without the extra tests.

Fixes PR59763

[Mordante]

Trigger CI to validate merge conflict resolution.

libcxx/include/__format/formatter_string.h

 struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<const _CharT*, _CharT>
     : public __formatter_string<_CharT> {
   using _Base = __formatter_string<_CharT>;
 
   _LIBCPP_HIDE_FROM_ABI auto format(const _CharT* __str, auto& __ctx) const -> decltype(__ctx.out()) {
     _LIBCPP_ASSERT(__str, "The basic_format_arg constructor should have "
                           "prevented an invalid pointer.");
 
+    __format_spec::__parsed_specifications<_CharT> __specs = _Base::__parser_.__get_parsed_std_specifications(__ctx);
+#  if _LIBCPP_STD_VER > 20
+    if (_Base::__parser_.__type_ == __format_spec::__type::__debug)
+      return __formatter::__format_escaped_string(basic_string_view<_CharT>{__str}, __ctx.out(), __specs);
+#  endif
+
     // When using a center or right alignment and the width option the length
     // of __str must be known to add the padding upfront. This case is handled
     // by the base class by converting the argument to a basic_string_view.
     //
     // When using left alignment and the width option the padding is added
     // after outputting __str so the length can be determined while outputting
     // __str. The same holds true for the precision, during outputting __str it
     // can be validated whether the precision threshold has been reached. For
     // now these optimizations aren't implemented. Instead the base class
     // handles these options.
     // TODO FMT Implement these improvements.
-    __format_spec::__parsed_specifications<_CharT> __specs = _Base::__parser_.__get_parsed_std_specifications(__ctx);
     if (__specs.__has_width() || __specs.__has_precision())
       return __formatter::__write_string(basic_string_view<_CharT>{__str}, __ctx.out(), __specs);
 
     // No formatting required, copy the string to the output.
     auto __out_it = __ctx.out();
     while (*__str)
       *__out_it++ = *__str++;
     return __out_it;

libcxx/test/std/utilities/format/format.tuple/format.functions.tests.h

 template <class CharT, class TestFunction, class ExceptionTest>
 void test_pair_int_int(TestFunction check, ExceptionTest check_exception) {
   test_tuple_or_pair_int_int<CharT>(check, check_exception, std::make_pair(42, 99));
 }
 
 template <class CharT, class TestFunction, class ExceptionTest>
 void test_pair_int_string(TestFunction check, ExceptionTest check_exception) {
   test_tuple_or_pair_int_string<CharT>(check, check_exception, std::make_pair(42, SV("hello")));
+  test_tuple_or_pair_int_string<CharT>(check, check_exception, std::make_pair(42, STR("hello")));
+  test_tuple_or_pair_int_string<CharT>(check, check_exception, std::make_pair(42, CSTR("hello")));
 }
 
 //
 // tuple tests
 //
 
 template <class CharT, class TestFunction, class ExceptionTest>
 void test_tuple_int(TestFunction check, ExceptionTest check_exception) {

 template <class CharT, class TestFunction, class ExceptionTest>
 void test_tuple_int_int(TestFunction check, ExceptionTest check_exception) {
   test_tuple_or_pair_int_int<CharT>(check, check_exception, std::make_tuple(42, 99));
 }
 
 template <class CharT, class TestFunction, class ExceptionTest>
 void test_tuple_int_string(TestFunction check, ExceptionTest check_exception) {
   test_tuple_or_pair_int_string<CharT>(check, check_exception, std::make_tuple(42, SV("hello")));
+  test_tuple_or_pair_int_string<CharT>(check, check_exception, std::make_tuple(42, STR("hello")));
+  test_tuple_or_pair_int_string<CharT>(check, check_exception, std::make_tuple(42, CSTR("hello")));
 }
 
 //
 // nested tests
 //
 
 template <class CharT, class TestFunction, class ExceptionTest, class Nested>
 void test_nested(TestFunction check, ExceptionTest check_exception, Nested&& input) {