[Bug fortran/99922] Bind(C) with assumed length character should work

["kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99922

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-04-06
             Status|UNCONFIRMED                 |NEW
                 CC|                            |kargl at gcc dot gnu.org
           Priority|P3                          |P4
     Ever confirmed|0                           |1

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Brad Richardson from comment #0)
> 
> So this is supposed to be allowed, and I can confirm that I can compile and
> execute the above example and obtain the expected result with Intel (ifort
> and icc).
> 

What result did Intel produce?

This patch suppresses the error message, which allows the code
to compile.  gfortran may produces wrong code.  Someone else can
investigate that issue

diff --git a/gcc/fortran/decl.c b/gcc/fortran/decl.c
index 9039c9dca2a..b10a92ca234 100644
--- a/gcc/fortran/decl.c
+++ b/gcc/fortran/decl.c
@@ -1549,19 +1549,21 @@ gfc_verify_c_interop_param (gfc_symbol *sym)
                             sym->ns->proc_name->name);
            }

-          /* Character strings are only C interoperable if they have a
-             length of 1.  */
-          if (sym->ts.type == BT_CHARACTER && !sym->attr.dimension)
+          /* In F2008 (and earlier?) a character string is only C
+            interoperable if it has a length of 1.  With F2018, if the
+            string is a dummy argument, it can have an assumed length if
+            the formal argument is CFI_cdesc_t.  */
+          if (sym->ts.type == BT_CHARACTER && !sym->attr.dimension
+             && !((gfc_option.allow_std & GFC_STD_F2018) && sym->attr.dummy))
            {
              gfc_charlen *cl = sym->ts.u.cl;
+
              if (!cl || !cl->length || cl->length->expr_type != EXPR_CONSTANT
                   || mpz_cmp_si (cl->length->value.integer, 1) != 0)
                {
-                 gfc_error ("Character argument %qs at %L "
-                            "must be length 1 because "
-                            "procedure %qs is BIND(C)",
-                            sym->name, &sym->declared_at,
-                            sym->ns->proc_name->name);
+                 gfc_error ("Character argument %qs at %L must be length 1 "
+                            "because procedure %qs is BIND(C)", sym->name, 
+                            &sym->declared_at, sym->ns->proc_name->name);
                  retval = false;
                }
            }