objtuple: Go out of the way to support comparison of subclasses.

Two things are handled here: allow to compare native subtypes of tuple,
e.g. namedtuple (TODO: should compare type too, currently compared
duck-typedly by content). Secondly, allow user sunclasses of tuples
(and its subtypes) be compared either. "Magic" I did previously in
objtype.c covers only one argument (lhs is many), so we're in trouble
when lhs is native type - there's no other option besides handling
rhs in special manner. Fortunately, this patch outlines approach with
fast path for native types.

py/obj.h

@@ -401,6 +401,7 @@ mp_obj_t mp_obj_new_module(qstr module_name);
 mp_obj_type_t *mp_obj_get_type(mp_const_obj_t o_in);
 const char *mp_obj_get_type_str(mp_const_obj_t o_in);
 bool mp_obj_is_subclass_fast(mp_const_obj_t object, mp_const_obj_t classinfo); // arguments should be type objects
+mp_obj_t mp_instance_cast_to_native_base(mp_const_obj_t self_in, mp_const_obj_t native_type);
 
 void mp_obj_print_helper(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind);
 void mp_obj_print(mp_obj_t o, mp_print_kind_t kind);

py/objtuple.c

@@ -99,12 +99,20 @@ mp_obj_t mp_obj_tuple_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const m
 
 // Don't pass MP_BINARY_OP_NOT_EQUAL here
 STATIC bool tuple_cmp_helper(int op, mp_obj_t self_in, mp_obj_t another_in) {
-    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_tuple));
-    if (!MP_OBJ_IS_TYPE(another_in, &mp_type_tuple)) {
-        return false;
+    mp_obj_type_t *self_type = mp_obj_get_type(self_in);
+    if (self_type->getiter != tuple_getiter) {
+        assert(0);
     }
+    mp_obj_type_t *another_type = mp_obj_get_type(another_in);
     mp_obj_tuple_t *self = self_in;
     mp_obj_tuple_t *another = another_in;
+    if (another_type->getiter != tuple_getiter) {
+        // Slow path for user subclasses
+        another = mp_instance_cast_to_native_base(another, &mp_type_tuple);
+        if (another == MP_OBJ_NULL) {
+            return false;
+        }
+    }
 
     return mp_seq_cmp_objs(op, self->items, self->len, another->items, another->len);
 }

py/objtype.c

@@ -845,6 +845,15 @@ STATIC mp_obj_t mp_builtin_isinstance(mp_obj_t object, mp_obj_t classinfo) {
 
 MP_DEFINE_CONST_FUN_OBJ_2(mp_builtin_isinstance_obj, mp_builtin_isinstance);
 
+mp_obj_t mp_instance_cast_to_native_base(mp_const_obj_t self_in, mp_const_obj_t native_type) {
+    mp_obj_type_t *self_type = mp_obj_get_type(self_in);
+    if (!mp_obj_is_subclass_fast(self_type, native_type)) {
+        return MP_OBJ_NULL;
+    }
+    mp_obj_instance_t *self = (mp_obj_instance_t*)self_in;
+    return self->subobj[0];
+}
+
 /******************************************************************************/
 // staticmethod and classmethod types (probably should go in a different file)
 

tests/basics/subclass_native_cmp.py

@@ -0,0 +1,9 @@
+# Test calling non-special method inherited from native type
+
+class mytuple(tuple):
+    pass
+
+t = mytuple((1, 2, 3))
+print(t)
+print(t == (1, 2, 3))
+print((1, 2, 3) == t)