Fortran: improve error recovery for invalid coarray function declarations

gcc/fortran/ChangeLog:

	PR fortran/104210
	* arith.cc (eval_intrinsic): Avoid NULL pointer dereference.
	(gfc_zero_size_array): Likewise.

gcc/testsuite/ChangeLog:

	PR fortran/104210
	* gfortran.dg/pr104210.f90: New test.

gcc/fortran/arith.cc

@@ -1489,6 +1489,9 @@ eval_intrinsic (gfc_intrinsic_op op,
   int unary;
   arith rc;
 
+  if (!op1)
+    return NULL;
+
   gfc_clear_ts (&temp.ts);
 
   switch (op)
@@ -1703,11 +1706,11 @@ eval_type_intrinsic0 (gfc_intrinsic_op iop, gfc_expr *op)
 
 /* Return nonzero if the expression is a zero size array.  */
 
-static int
+static bool
 gfc_zero_size_array (gfc_expr *e)
 {
-  if (e->expr_type != EXPR_ARRAY)
-    return 0;
+  if (e == NULL || e->expr_type != EXPR_ARRAY)
+    return false;
 
   return e->value.constructor == NULL;
 }

gcc/testsuite/gfortran.dg/pr104210.f90

@@ -0,0 +1,15 @@
+! { dg-do compile }
+! { dg-options "-fcoarray=single" }
+! PR fortran/104210
+! Contributed by G.Steinmetz
+
+function f()      ! { dg-error "shall not be a coarray" }
+  integer :: f[*]
+end
+program p
+  interface
+     function f() ! { dg-error "shall not be a coarray" }
+       integer :: f[*]
+     end
+  end interface
+end