When building relatively recent gcc ports (with C++ in them) against
libc++ 17, you get errors similar to:
In file included from /wrkdirs/usr/ports/lang/gcc12/work/gcc-12.2.0/gcc/cp/module.cc:208:
In file included from /wrkdirs/usr/ports/lang/gcc12/work/gcc-12.2.0/gcc/system.h:239:
In file included from /usr/include/c++/v1/vector:321:
In file included from /usr/include/c++/v1/__format/formatter_bool.h:20:
In file included from /usr/include/c++/v1/__format/formatter_integral.h:32:
In file included from /usr/include/c++/v1/locale:202:
/usr/include/c++/v1/__locale:546:5: error: '__abi_tag__' attribute only applies to structs, variables, functions, and namespaces
546 | _LIBCPP_INLINE_VISIBILITY
| ^
/usr/include/c++/v1/__config:813:37: note: expanded from macro '_LIBCPP_INLINE_VISIBILITY'
813 | # define _LIBCPP_INLINE_VISIBILITY _LIBCPP_HIDE_FROM_ABI
| ^
/usr/include/c++/v1/__config:792:26: note: expanded from macro '_LIBCPP_HIDE_FROM_ABI'
792 | __attribute__((__abi_tag__(_LIBCPP_TOSTRING(_LIBCPP_VERSIONED_IDENTIFIER))))
| ^
In file included from /wrkdirs/usr/ports/lang/gcc12/work/gcc-12.2.0/gcc/cp/module.cc:208:
In file included from /wrkdirs/usr/ports/lang/gcc12/work/gcc-12.2.0/gcc/system.h:239:
In file included from /usr/include/c++/v1/vector:321:
In file included from /usr/include/c++/v1/__format/formatter_bool.h:20:
In file included from /usr/include/c++/v1/__format/formatter_integral.h:32:
In file included from /usr/include/c++/v1/locale:202:
/usr/include/c++/v1/__locale:547:37: error: expected ';' at end of declaration list
547 | char_type toupper(char_type __c) const
| ^
/usr/include/c++/v1/__locale:553:48: error: too many arguments provided to function-like macro invocation
553 | const char_type* toupper(char_type* __low, const char_type* __high) const
| ^
/wrkdirs/usr/ports/lang/gcc12/work/gcc-12.2.0/gcc/../include/safe-ctype.h:146:9: note: macro 'toupper' defined here
146 | #define toupper(c) do_not_use_toupper_with_safe_ctype
| ^
This is because gcc/system.h includes safe-ctype.h which redefines ctype
macros such as toupper, tolower, etc to "poison" them.
However, it should only include the safe-ctype.h header *after* any C++
headers, such as <list>, <map>, <string>, etc, otherwise these might
transitively include internal ctype headers (such as with libc++ 17),
causing the above conflicts.
Fix it by moving the safe-ctype.h inclusion to later in gcc/system.h,
which solves this issue, and makes it possible to build against libc++
17.
See also: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111632
PR: 274041
Approved by: salvadore (maintainer)
MFH: 2023Q4
b7833e78f7