Improve type constraint checking in semantic_sub(), i.e. binary -.

[r21009]

diff --git a/parser.c b/parser.c
index 3b7e50f..287af0c 100644 (file)
--- a/parser.c
+++ b/parser.c
@@ -6455,14 +6455,25 @@ static void semantic_sub(binary_expression_t *expression)
                                         type_left, orig_type_left);
                expression->base.type = type_left;
        } else if(is_type_pointer(type_left) && is_type_pointer(type_right)) {
-               if(!pointers_compatible(type_left, type_right)) {
-                       errorf(HERE,
-                              "pointers to incompatible objects to binary '-' ('%T', '%T')",
+               type_t *const unqual_left  = get_unqualified_type(skip_typeref(type_left->pointer.points_to));
+               type_t *const unqual_right = get_unqualified_type(skip_typeref(type_right->pointer.points_to));
+               if (!types_compatible(unqual_left, unqual_right)) {
+                       errorf(&expression->base.source_position,
+                              "subtracting pointers to incompatible types '%T' and '%T'",
                               orig_type_left, orig_type_right);
+               } else if (!is_type_object(unqual_left)) {
+                       if (is_type_atomic(unqual_left, ATOMIC_TYPE_VOID)) {
+                               warningf(&expression->base.source_position,
+                                        "subtracting pointers to void");
+                       } else {
+                               errorf(&expression->base.source_position,
+                                      "subtracting pointers to non-object types '%T'",
+                                      orig_type_left);
+                       }
                }
                expression->base.type = type_ptrdiff_t;
        } else if (is_type_valid(type_left) && is_type_valid(type_right)) {
-               errorf(HERE, "invalid operands to binary '-' ('%T', '%T')",
+               errorf(HERE, "invalid operands of types '%T' and '%T' to binary '-'",
                       orig_type_left, orig_type_right);
        }
 }