On Thu, Dec 06, 2018 at 08:02:43PM +0100, Thomas Koenig wrote:
> Hi Steve,
>
> >>> PR fortran/88139
> >>> * dump-parse-tree.c (write_proc): Alternate return.
> >> I dissent with this patch. The introduced error is meaningless and, as
> >> mentioned by comment #3 in the PR, avoiding the ICE in dump-parse-tree
> >> is not directly the issue. The code should be rejected in parsing. In
> >> gcc-8.1 the invalid code is accepted (without an ICE) even without the
> >> -fc-prototypes flag: I haven't finished building the compiler with
> >> your changes yet to see whether that is still true afterwards, but at
> >> least the test case doesn't try this, so I strongly suspect the patch
> >> is incomplete to fix the PR.
> >
> > Comment #3 does not contain a patch to fix the problem elsewhere.
>
> I know :-)
>
> > In F2003, 15.2.6 "Interoperability of procedures and procedure interfaces",
> > I cannot find a prohibition on an alternate return in a subroutine
> > interface with BIND(C).
>
> I also does not allow this, and does not offer a valid interpretation
> of what it should mean.
>
> If it has a meaning, it should be translatable into something prescribed
> by the standard with -fc-prototypes.
>
> I have assigned the error to myself, so I will not forget to fix
> it before the gcc 9 release.
I think it comes down to F2018, 18.3.7, where one has
A Fortran procedure interface is interoperable with a C functioni
prototype if
(1) ...
(2) ...
(3) ...
(4) ...
(5) any dummy argument without the VALUE attribute corresponds to
a formal parameter of the prototype that is of a pointer type,
and either (4 bullets which cannot be satisfied).
I suppose we should check what other compilers do on the
testcase, but I only have access to gfortran.
BTW, write_proc() starts to write out the prototype before the
argument list is checked. If the current gfc_error
is trigger, you get
void foo (Error: Cannot convert %qs to interoperable type...
I think you want to scan the formal argument list for errors
before writing out "void foo (".
--
Steve
