It seems prudent to add C++26 now that the first C++26 papers have been
approved. I followed commit r11-6920 as well as r8-3237.
Since C++23 is essentially finished and its __cplusplus value has
settled to 202302L, I've updated cpp_init_builtins and marked
-std=c++2b Undocumented and made -std=c++23 no longer Undocumented.
I've verified the patch with a simple test, exercising the new
directives. Don't forget to update your GXX_TESTSUITE_STDS!
This patch does not add -Wc++26-extensions.
gcc/c-family/ChangeLog:
* c-common.h (cxx_dialect): Add cxx26 as a dialect.
* c-opts.cc (set_std_cxx26): New.
(c_common_handle_option): Set options when -std={c,gnu}++2{c,6} is
enabled.
(c_common_post_options): Adjust comments.
* c.opt: Add options for -std=c++26, std=c++2c, -std=gnu++26,
and -std=gnu++2c.
(std=c++2b): Mark as Undocumented.
(std=c++23): No longer Undocumented.
gcc/ChangeLog:
* doc/cpp.texi (__cplusplus): Document value for -std=c++26 and
-std=gnu++26. Document that for C++23, its value is 202302L.
* doc/invoke.texi: Document -std=c++26 and -std=gnu++26.
* dwarf2out.cc (highest_c_language): Handle GNU C++26.
(gen_compile_unit_die): Likewise.
libcpp/ChangeLog:
* include/cpplib.h (c_lang): Add CXX26 and GNUCXX26.
* init.cc (lang_defaults): Add rows for CXX26 and GNUCXX26.
(cpp_init_builtins): Set __cplusplus to 202400L for C++26.
Set __cplusplus to 202302L for C++23.
gcc/testsuite/ChangeLog:
* lib/target-supports.exp (check_effective_target_c++23): Return
1 also if check_effective_target_c++26.
(check_effective_target_c++23_down): New.
(check_effective_target_c++26_only): New.
(check_effective_target_c++26): New.
* g++.dg/cpp23/cplusplus.C: Adjust expected value.
* g++.dg/cpp26/cplusplus.C: New test.