Fix assigning-non-slot false positive with setattr (#5457)

* Fix assigning-non-slot false positive with setattr

Previously, if a class was slotted and overrode `__setattr__`,
`assigning-non-slot` would be issued when assigning to attributes.  With
`__setattr__` defined, we cannot infer if it is an error to assign to an
attribute, so we suppress the error.

Fix #3793

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/functional/a/assign/assigning_non_slot.py b/tests/functional/a/assign/assigning_non_slot.py
index cf673692f..2cd1483e0 100644
--- a/tests/functional/a/assign/assigning_non_slot.py
+++ b/tests/functional/a/assign/assigning_non_slot.py
@@ -173,3 +173,30 @@ class Cls(Generic[TYPE]):
 
     def __init__(self, value):
         self.value = value
+
+
+class ClassDefiningSetattr(object):
+    __slots__ = ["foobar"]
+
+    def __init__(self):
+        self.foobar = {}
+
+    def __setattr__(self, name, value):
+        if name == "foobar":
+            super().__setattr__(name, value)
+        else:
+            self.foobar[name] = value
+
+
+class ClassWithParentDefiningSetattr(ClassDefiningSetattr):
+    __slots__ = []
+
+
+def dont_emit_for_defined_setattr():
+    inst = ClassDefiningSetattr()
+    # This should not emit because we can't reason about what happens with
+    # classes defining __setattr__
+    inst.non_existent = "non-existent"
+
+    child = ClassWithParentDefiningSetattr()
+    child.non_existent = "non-existent"