https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119049
--- Comment #1 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Thomas Koenig <tkoe...@gcc.gnu.org>: https://gcc.gnu.org/g:21ca9153ebe525b077ac96811cfd48be6b259e7e commit r15-7817-g21ca9153ebe525b077ac96811cfd48be6b259e7e Author: Thomas Koenig <tkoe...@gcc.gnu.org> Date: Tue Mar 4 20:13:19 2025 +0100 C prototypes for external arguments; add warning for mismatch. The problem was that we were not handling external dummy arguments with -fc-prototypes-external. In looking at this, I found that we were not warning about external procedures with different argument lists. This can actually be legal (see the two test cases) but creates a problem for the C prototypes: If we have something like subroutine foo(a,n) external a if (n == 1) call a(1) if (n == 2) call a(2,3) end subroutine foo then, pre-C23, we could just have written out the prototype as void foo_ (void (*a) (), int *n); but this is illegal in C23. What to do? I finally chose to warn about the argument mismatch, with a new option. Warn only because the code above is legal, but include in -Wall because such code seems highly suspect. This option is also implied in -fc-prototypes-external. I also put a warning in the generated header file in that case, so users have a chance to see what is going on (especially since gcc now defaults to C23). gcc/fortran/ChangeLog: PR fortran/119049 PR fortran/119074 * dump-parse-tree.cc (seen_conflict): New static varaible. (gfc_dump_external_c_prototypes): Initialize it. If it was set, write out a warning that -std=c23 will not work. (write_proc): Move the work of actually writing out the formal arglist to... (write_formal_arglist): New function. Handle external dummy parameters and their argument lists. If there were mismatched arguments, output an empty argument list in pre-C23 style. * gfortran.h (struct gfc_symbol): Add ext_dummy_arglist_mismatch flag and formal_at. * invoke.texi: Document -Wexternal-argument-mismatch. * lang.opt: Put it in. * resolve.cc (resolve_function): If warning about external argument mismatches, build a formal from actual arglist the first time around, and later compare and warn. (resolve_call): Likewise gcc/testsuite/ChangeLog: PR fortran/119049 PR fortran/119074 * gfortran.dg/interface_55.f90: New test. * gfortran.dg/interface_56.f90: New test.
