https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109162
--- Comment #11 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Tomasz Kaminski <tkami...@gcc.gnu.org>: https://gcc.gnu.org/g:f62e5d720de829cf346b799f3463fee53728ba6c commit r15-9490-gf62e5d720de829cf346b799f3463fee53728ba6c Author: Tomasz KamiÅski <tkami...@redhat.com> Date: Fri Mar 28 09:30:22 2025 +0100 libstdc++: Implement formatter for ranges and range_formatter [PR109162] This patch implements formatter specialization for input_ranges and range_formatter class from P2286R8, as adjusted by P2585R1. The formatter for pair/tuple is not yet provided, making maps not formattable. This introduces an new _M_format_range member to internal __formatter_str, that formats range as _CharT as string, according to the format spec. This function transform any contiguous range into basic_string_view directly, by computing size if necessary. Otherwise, for ranges for which size can be computed (forward_range or sized_range) we use a stack buffer, if they are sufficiently small. Finally, we create a basic_string<_CharT> from the range, and format its content. In case when padding is specified, this is handled by firstly formatting the content of the range to the temporary string object. However, this can be only implemented if the iterator of the basic_format_context is internal type-erased iterator used by implementation. Otherwise a new basic_format_context would need to be created, which would require rebinding of handles stored in the arguments: note that format spec for element type could retrieve any format argument from format context, visit and use handle to format it. As basic_format_context provide no user-facing constructor, the user are not able to construct object of that type with arbitrary iterators. The signatures of the user-facing parse and format methods of the provided formatters deviate from the standard by constraining types of params: * _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. These types are later passed to possibly user-provided formatter specializations, that are required via formattable concept to only accept above types. Finally, the formatter<input_range, _CharT> specialization is implemented without using specialization of range-default-formatter exposition only template as base class, while providing same functionality. PR libstdc++/109162 libstdc++-v3/ChangeLog: * include/std/format (__format::__has_debug_format, _Pres_type::_Pres_seq) (_Pres_type::_Pres_str, __format::__Stackbuf_size): Define. (_Separators::_S_squares, _Separators::_S_parens, _Separators::_S_comma) (_Separators::_S_colon): Define additional constants. (_Spec::_M_parse_fill_and_align): Define overload accepting list of excluded characters for fill, and forward existing overload. (__formatter_str::_M_format_range): Define. (__format::_Buf_sink) Use __Stackbuf_size for size of array. (__format::__is_map_formattable, std::range_formatter) (std::formatter<_Rg, _CharT>): Define. * src/c++23/std.cc.in (std::format_kind, std::range_format) (std::range_formatter): Export. * testsuite/std/format/formatter/lwg3944.cc: Guarded tests with __glibcxx_format_ranges. * testsuite/std/format/formatter/requirements.cc: Adjusted for standard behavior. * testsuite/23_containers/vector/bool/format.cc: Test vector<bool> formatting. * testsuite/std/format/ranges/format_kind.cc: New test. * testsuite/std/format/ranges/formatter.cc: New test. * testsuite/std/format/ranges/sequence.cc: New test. * testsuite/std/format/ranges/string.cc: New test. Reviewed-by: Jonathan Wakely <jwak...@redhat.com> Signed-off-by: Tomasz KamiÅski <tkami...@redhat.com>
