https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105131
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:7da9a089608b0ca09683332ce014fb6184842724 commit r13-627-g7da9a089608b0ca09683332ce014fb6184842724 Author: Marek Polacek <pola...@redhat.com> Date: Fri Apr 1 16:55:58 2022 -0400 c: Implement new -Wenum-int-mismatch warning [PR105131] In C, an enumerated type is compatible with char, a signed integer type, or an unsigned integer type (6.7.2.2/5). Therefore this code compiles: enum E { l = -1, z = 0, g = 1 }; int foo(void); enum E foo(void) { return z; } if the underlying type of 'enum E' is 'int' (if not, we emit an error). This is different for typedefs, where C11 permits typedefs to be redeclared to the same type, but not to compatible types. In C++, the code above is invalid. It seems desirable to emit a warning in the C case, because it is probably a mistake and definitely a portability error, given that the choice of the underlying type is implementation-defined. To that end, this patch implements a new -Wenum-int-mismatch warning. Conveniently, we already have comptypes_check_enum_int to detect such mismatches. This warning is enabled by either -Wall or -Wc++-compat. PR c/105131 gcc/c-family/ChangeLog: * c.opt (Wenum-int-mismatch): New. gcc/c/ChangeLog: * c-decl.cc (diagnose_mismatched_decls): Warn about enum/integer type mismatches. * c-tree.h (comptypes_check_enum_int): Declare. * c-typeck.cc (comptypes): No longer static. gcc/ChangeLog: * doc/invoke.texi: Document -Wenum-int-mismatch. gcc/testsuite/ChangeLog: * gcc.dg/Wenum-int-mismatch-1.c: New test. * gcc.dg/Wenum-int-mismatch-2.c: New test. * gcc.dg/Wenum-int-mismatch-3.c: New test. * gcc.dg/Wenum-int-mismatch-4.c: New test. * gcc.dg/Wenum-int-mismatch-5.c: New test.
