Re: Fortran patches

[Steve Kargl <sgk@troutmask.apl.washington.edu>]

On Thu, Dec 06, 2018 at 02:08:54PM -0500, Fritz Reese wrote:
> On Wed, Dec 5, 2018 at 7:03 PM Steve Kargl
> >
> > > RE:
> > > >        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.
> >
> > 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'm disinclined to let a patch fester in bugzilla to only attain
> > the same fate as my patch to PR68544.
> 
> According to F2008 §15.3.7.2(5):
> 
> > any dummy argument without the VALUE attribute [...] is interoperable with an entity of the
> > referenced type (ISO/IEC 9899:1999, 6.2.5, 7.17, and 7.18.1) of the formal parameter
> 
> Regardless of whether or not we accept alternate returns in BIND(C)
> procedures, the compiler must be at least consistent: if we accept
> them (which gfortran currently does), then we should be able to dump
> the C prototype (with -fc-prototypes), providing a formal parameter
> interoperable with the type of the alternate return dummy argument; if
> we reject them, then we should issue the error in parsing (before
> handling by -fc-prototypes). In either case, the error message should
> not be obscure or meaningless. Even so, the patch here is inconsistent
> since we accept the code, but issue an error when attempting to dump
> the C prototype.

Here's an alternative patch that would reject a subroutine
with an alternate return dummy argument with the bind(c)
attributes.  I'm still trying to determine if the code 
should be legal.  The c.l.f thread I started isn't helping :(

Index: decl.c
===================================================================
--- decl.c	(revision 266766)
+++ decl.c	(working copy)
@@ -7467,6 +7467,7 @@ gfc_match_subroutine (void)
   match is_bind_c;
   char peek_char;
   bool allow_binding_name;
+  locus loc;
 
   if (gfc_current_state () != COMP_NONE
       && gfc_current_state () != COMP_INTERFACE
@@ -7532,6 +7533,8 @@ gfc_match_subroutine (void)
   /* Here, we are just checking if it has the bind(c) attribute, and if
      so, then we need to make sure it's all correct.  If it doesn't,
      we still need to continue matching the rest of the subroutine line.  */
+  gfc_gobble_whitespace ();
+  loc = gfc_current_locus;
   is_bind_c = gfc_match_bind_c (sym, allow_binding_name);
   if (is_bind_c == MATCH_ERROR)
     {
@@ -7543,6 +7546,8 @@ gfc_match_subroutine (void)
 
   if (is_bind_c == MATCH_YES)
     {
+      gfc_formal_arglist *arg;
+
       /* The following is allowed in the Fortran 2008 draft.  */
       if (gfc_current_state () == COMP_CONTAINS
 	  && sym->ns->proc_name->attr.flavor != FL_MODULE
@@ -7556,8 +7561,17 @@ gfc_match_subroutine (void)
           gfc_error ("Missing required parentheses before BIND(C) at %C");
           return MATCH_ERROR;
         }
-      if (!gfc_add_is_bind_c (&(sym->attr), sym->name,
-			      &(sym->declared_at), 1))
+
+      /* Scan the dummy arguments for an alternate return.  */
+      for (arg = sym->formal; arg; arg = arg->next)
+	if (!arg->sym)
+	  {
+	    gfc_error ("Alternate return dummy argument cannot appear in a "
+		       "SUBROUTINE with the BIND(C) attribute at %L", &loc);
+	    return MATCH_ERROR;
+	  }
+
+      if (!gfc_add_is_bind_c (&(sym->attr), sym->name, &(sym->declared_at), 1))
         return MATCH_ERROR;
     }

-- 
steve