libstdc++: Implement formatters for pair and tuple [PR109162]

This patch implements formatter specializations for pair and tuple form
P2286R8. In addition using 'm` and range_format::map (from P2585R1) for
ranges are now supported.

The formatters for pairs and tuples whose corresponding elements are the same
(after applying remove_cvref_t) derive from the same __tuple_formatter class.
This reduce the code duplication, as most of the parsing and formatting is the
same in such cases. We use a custom reduced implementation of the tuple
(__formatters_storage) to store the elements formatters.

Handling of the padding (width and fill) options, is extracted to
__format::__format_padded function, that is used both by __tuple_formatter and
range_formatter. To reduce number of instantations range_formatter::format
triggers, we cast incoming range to __format::__maybe_const_range<_Rg, _CharT>&,
before formatting it.

As in the case of previous commits, the signatures of the user-facing parse
and format methods of the provided formatters deviate from the standard by
constraining types of parameters:
* _CharT is constrained __formatter::__char
* basic_format_parse_context<_CharT> for parse argument
* basic_format_context<_Out, _CharT> for format second argument
The standard specifies last three of above as unconstrained types.

Finally, test for tuple-like std::array and std::ranges::subrange,
that illustrate that they remain formatted as ranges.

	PR libstdc++/109162

libstdc++-v3/ChangeLog:

	* include/std/format (__formatter_int::_M_format_character_escaped)
	(__formatter_str::format): Use __sink.out() to produce _Sink_iter.
	(__format::__const_formattable_range): Moved closer to range_formatter.
	(__format::__maybe_const_range): Use `__conditional_t` and moved closer
	to range_formatter.
	(__format::__format_padded, __format::maybe_const)
	(__format::__indexed_formatter_storage, __format::__tuple_formatter)
	(std::formatter<pair<_Fp, _Sp>, _CharT>>)
	(std::formatter<tuple<_Tps...>, _CharT): Define.
	(std::formatter<_Rg, _CharT>::format): Cast incoming range to
	__format::__maybe_const_range<_Rg, _CharT>&.
	(std::formatter<_Rg, _CharT>::_M_format): Extracted from format,
	and use __format_padded.
	(std::formatter<_Rg, _CharT>::_M_format_no_padding): Rename...
	(std::formatter<_Rg, _CharT>::_M_format_elems): ...to this.
	(std::formatter<_Rg, _CharT>::_M_format_with_padding): Extracted as
	__format_padded.
	* testsuite/util/testsuite_iterators.h (test_input_range_nocopy):
	Define.
	* testsuite/std/format/ranges/formatter.cc: Tests for `m` specifier.
	* testsuite/std/format/ranges/sequence.cc: Tests for array and subrange.
	* testsuite/std/format/ranges/map.cc: New test.
	* testsuite/std/format/tuple.cc: New test.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>

0 files changed, 0 insertions, 0 deletions