Check native object in case of early access

If a native displayio object is accessed before it's super().__init__()
has been called, then a placeholder is given that will cause a crash if
accessed. This is tricky to get right so we detect this case and raise
a NotInplementedError instead of crashing.

Fixes #1881

2 files changed, 12 insertions, 0 deletions

diff --git a/py/objtype.c b/py/objtype.c
index 88e918827..5133d849f 100644
--- a/py/objtype.c
+++ b/py/objtype.c
@@ -117,6 +117,16 @@ mp_obj_instance_t *mp_obj_new_instance(const mp_obj_type_t *class, const mp_obj_
     return o;
 }
 
+// When instances are first created they have the base_init wrapper as their native parent's
+// instance because make_new combines __new__ and __init__. This object is invalid for the native
+// code so it must call this method to ensure that the given object has been __init__'d and is
+// valid.
+void mp_obj_assert_native_inited(mp_obj_t native_object) {
+    if (native_object == MP_OBJ_FROM_PTR(&native_base_init_wrapper_obj)) {
+        mp_raise_NotImplementedError(translate("Call super().__init__() before accessing native object."));
+    }
+}
+
 // TODO
 // This implements depth-first left-to-right MRO, which is not compliant with Python3 MRO
 // http://python-history.blogspot.com/2010/06/method-resolution-order.html
diff --git a/py/objtype.h b/py/objtype.h
index 13613f01f..a32c87496 100644
--- a/py/objtype.h
+++ b/py/objtype.h
@@ -37,6 +37,8 @@ typedef struct _mp_obj_instance_t {
     // TODO maybe cache __getattr__ and __setattr__ for efficient lookup of them
 } mp_obj_instance_t;
 
+void mp_obj_assert_native_inited(mp_obj_t native_object);
+
 #if MICROPY_CPYTHON_COMPAT
 // this is needed for object.__new__
 mp_obj_instance_t *mp_obj_new_instance(const mp_obj_type_t *cls, const mp_obj_type_t **native_base);