Fix hasattr(settings) AssertionError with mypy 0.990 (#1239)

Fixes #1235. It seems this was caused by a new feature in mypy 0.990 involving `hasattr()`.

Author: intgr

mypy_django_plugin/transformers/settings.py

@@ -21,7 +21,9 @@ def get_user_model_hook(ctx: FunctionContext, django_context: DjangoContext) ->
 
 
 def get_type_of_settings_attribute(ctx: AttributeContext, django_context: DjangoContext) -> MypyType:
-    assert isinstance(ctx.context, MemberExpr)
+    if not isinstance(ctx.context, MemberExpr):
+        return ctx.default_attr_type
+
     setting_name = ctx.context.name
 
     typechecker_api = helpers.get_typechecker_api(ctx)

tests/typecheck/test_settings.yml

@@ -45,3 +45,16 @@
             content: |
                 from pathlib import Path
                 MEDIA_ROOT = Path()
+
+-   case: settings_hasattr
+    main: |
+      from django.conf import settings
+      if hasattr(settings, 'AUTH_USER_MODEL') and settings.AUTH_USER_MODEL:
+          reveal_type(settings.AUTH_USER_MODEL)
+      if hasattr(settings, 'NON_EXISTANT_SETTING') and settings.NON_EXISTANT_SETTING:
+          reveal_type(settings.NON_EXISTANT_SETTING)
+    out: |
+      main:3: note: Revealed type is "builtins.str"
+      main:4: error: 'Settings' object has no attribute 'NON_EXISTANT_SETTING'
+      main:5: error: 'Settings' object has no attribute 'NON_EXISTANT_SETTING'
+      main:5: note: Revealed type is "Any"