[Bug fortran/126968] ICE on invalid use of ASSOCIATE

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126968

Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2026-08-20

--- Comment #1 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
Possible fix, still testing. This is touching areas Paul is working so I will
hold for a while after I finish testing here.

diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index 5a7b0a7acb3..71ac7782beb 100644
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -6935,7 +6935,7 @@ void
 gfc_fixup_inferred_type_refs (gfc_expr *e)
 {
   gfc_ref *ref, *new_ref;
-  gfc_symbol *sym, *derived;
+  gfc_symbol *sym, *derived, *dt;
   gfc_expr *target;
   sym = e->symtree->n.sym;

@@ -7036,17 +7036,47 @@ gfc_fixup_inferred_type_refs (gfc_expr *e)
        }
     }

-  /* Proceed as far as the first component reference and ensure that the
-     correct derived type is being used.  */
+  /* The type used to build the component references at parse time was only
+     a guess, so they can point into a different derived type that happens
+     to have a component of the same name.  Bind each one by name to the
+     corrected type.  */
+  dt = derived;
   for (ref = e->ref; ref; ref = ref->next)
-    if (ref->type == REF_COMPONENT)
-      {
-       if (ref->u.c.component->name[0] != '_')
-         ref->u.c.sym = derived;
-       else
+    {
+      gfc_component *c;
+
+      if (ref->type != REF_COMPONENT)
+       continue;
+
+      /* The '_data', '_vptr' and '_len' fields belong to the class
+        container, and 'derived' already is the type that follows '_data'.  */
+      if (ref->u.c.component->name[0] == '_')
+       {
          ref->u.c.sym = sym->ts.u.derived;
+         continue;
+       }
+
+      if (!dt)
        break;
-      }
+
+      c = gfc_find_component (dt, ref->u.c.component->name, true, true, NULL);
+      if (!c)
+       {
+         gfc_error ("%qs at %L is not a member of the %qs structure",
+                    ref->u.c.component->name, &e->where, dt->name);
+         return;
+       }
+
+      ref->u.c.sym = dt;
+      ref->u.c.component = c;
+
+      if (c->ts.type == BT_DERIVED)
+       dt = c->ts.u.derived;
+      else if (c->ts.type == BT_CLASS && CLASS_DATA (c))
+       dt = CLASS_DATA (c)->ts.u.derived;
+      else
+       dt = NULL;
+    }

   /* Verify that the type inference mechanism has not introduced a spurious
      array reference.  This can happen with an associate name, whose selector