[libc++][format] Fixes default string alignment.

[Mordante]

Summary

Fixes https://llvm.org/PR58315

[Mordante]

CI fixes.

libcxx/include/__format/formatter_string.h

#  endif
 
     return __formatter::__write_string(__str, __ctx.out(), __parser_.__get_parsed_std_specifications(__ctx));
   }
 
 #  if _LIBCPP_STD_VER > 20
   _LIBCPP_HIDE_FROM_ABI constexpr void set_debug_format() { __parser_.__type_ = __format_spec::__type::__debug; }
 #  endif
 
-  __format_spec::__parser<_CharT> __parser_;
+  __format_spec::__parser<_CharT> __parser_{.__alignment_ = __format_spec::__alignment::__left};
 };
 
 // Formatter const char*.
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<const _CharT*, _CharT>
     : public __formatter_string<_CharT> {
   using _Base = __formatter_string<_CharT>;
 

libcxx/test/std/utilities/format/format.functions/format_tests.h

void format_test_string(const W& world, const U& universe, TestFunction check, ExceptionTest check_exception) {
   // Unused argument is ignored. TODO FMT what does the Standard mandate?
   check(SV("hello world"), SV("hello {}"), world, universe);
   check(SV("hello world and universe"), SV("hello {} and {}"), world, universe);
   check(SV("hello world"), SV("hello {0}"), world, universe);
   check(SV("hello universe"), SV("hello {1}"), world, universe);
   check(SV("hello universe and world"), SV("hello {1} and {0}"), world, universe);
 
   check(SV("hello world"), SV("hello {:_>}"), world);
+  check(SV("hello world   "), SV("hello {:8}"), world);
   check(SV("hello    world"), SV("hello {:>8}"), world);
   check(SV("hello ___world"), SV("hello {:_>8}"), world);
   check(SV("hello _world__"), SV("hello {:_^8}"), world);
   check(SV("hello world___"), SV("hello {:_<8}"), world);
 
   check(SV("hello >>>world"), SV("hello {:>>8}"), world);
   check(SV("hello <<<world"), SV("hello {:<>8}"), world);
   check(SV("hello ^^^world"), SV("hello {:^>8}"), world);

 }
 
 template <class CharT, class TestFunction, class ExceptionTest>
 void format_test_char(TestFunction check, ExceptionTest check_exception) {
 
   // ***** Char type *****
   // *** align-fill & width ***
   check(SV("answer is '*     '"), SV("answer is '{:6}'"), CharT('*'));
-
   check(SV("answer is '     *'"), SV("answer is '{:>6}'"), CharT('*'));
   check(SV("answer is '*     '"), SV("answer is '{:<6}'"), CharT('*'));
   check(SV("answer is '  *   '"), SV("answer is '{:^6}'"), CharT('*'));
 
   check(SV("answer is '*     '"), SV("answer is '{:6c}'"), CharT('*'));
   check(SV("answer is '     *'"), SV("answer is '{:>6c}'"), CharT('*'));
   check(SV("answer is '*     '"), SV("answer is '{:<6c}'"), CharT('*'));
   check(SV("answer is '  *   '"), SV("answer is '{:^6c}'"), CharT('*'));