[Bug fortran/109512] New: accepts implicit dummy procedure even with "implicit none (external)"

[Bug fortran/109512] New: accepts implicit dummy procedure even with "implicit none (external)"

[sebastien at debian dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109512

            Bug ID: 109512
           Summary: accepts implicit dummy procedure even with "implicit
                    none (external)"
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sebastien at debian dot org
  Target Milestone: ---

gfortran compiles the following source without error:

subroutine foo(bar)
  implicit none (external)
  call bar(1)
end subroutine foo

However my understanding is that it should reject it, because "bar" is an
implicit dummy procedure, which is forbidden by "implicit none (external)".

Note that this is not the same issue as Bug 100972, which was not about dummy
procedures.

[Bug fortran/109512] accepts implicit dummy procedure even with "implicit none (external)"

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109512

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |kargl at gcc dot gnu.org
   Last reconfirmed|                            |2023-04-14

--- Comment #1 from kargl at gcc dot gnu.org ---
Confirmed.

8.7 IMPLICIT statement
...
An IMPLICIT NONE statement can indicate ..., or that external and
dummy procedures need to be explicitly given the EXTERNAL attribute.

'bar' is clearly a dummy procedure, so 'externa bar' is required.

[Bug fortran/109512] accepts implicit dummy procedure even with "implicit none (external)"

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109512

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4

[Bug fortran/109512] accepts implicit dummy procedure even with "implicit none (external)"

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109512

--- Comment #2 from kargl at gcc dot gnu.org ---
This patch catches the need for an external attribute.

diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index 6e42397c2ea..1e19712b413 100644
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -3818,6 +3818,16 @@ resolve_call (gfc_code *c)
   /* Resume assumed_size checking.  */
   need_full_assumed_size--;

+  /* If 'implicit none (external)' and the symbol is a dummy argument,
+     check for an 'external' attribute.  */
+  if (csym->ns->has_implicit_none_export
+      && csym->attr.external == 0 && csym->attr.dummy == 1)
+    {
+      gfc_error ("Dummy procedure %qs at %C requires an EXTERNAL attribute",
+                csym->name);
+      return false;
+    }
+
   /* If external, check for usage.  */
   if (csym && is_external_proc (csym))
     resolve_global_procedure (csym, &c->loc, 1);

A dejagnu-ified testcase.

! { dg-do compile }
subroutine foo(bar)
  implicit none (external)
  call bar(1)        ! { dg-error "requires an EXTERNAL attribute" }
end subroutine foo