Fix #2998: correctly handle MemberExpr in infer_partial_type (#3064)

Fix #2998

Author: kirbyfan64

mypy/checker.py

@@ -1617,7 +1617,7 @@ def infer_partial_type(self, name: Var, lvalue: Lvalue, init_type: Type) -> bool
             partial_type = PartialType(None, name, [init_type])
         elif isinstance(init_type, Instance):
             fullname = init_type.type.fullname()
-            if (isinstance(lvalue, NameExpr) and
+            if (isinstance(lvalue, (NameExpr, MemberExpr)) and
                     (fullname == 'builtins.list' or
                      fullname == 'builtins.set' or
                      fullname == 'builtins.dict') and

test-data/unit/check-inference.test

@@ -1267,8 +1267,22 @@ class A:
     def f(self) -> None:
         # Attributes aren't supported right now.
         self.a = [] # E: Need type annotation for variable
-        self.a.append(1) # E: Cannot determine type of 'a'
-        self.a.append('') # E: Cannot determine type of 'a'
+        self.a.append(1)
+        self.a.append('')
+[builtins fixtures/list.pyi]
+[out]
+
+[case testInferListInitializedToEmptyInClassBodyAndOverriden]
+from typing import List
+
+class A:
+    def __init__(self) -> None:
+        self.x = [] # E: Need type annotation for variable
+
+class B(A):
+    @property
+    def x(self) -> List[int]:
+        return [123]
 [builtins fixtures/list.pyi]
 [out]
 

test-data/unit/fixtures/list.pyi

@@ -28,3 +28,5 @@ class function: pass
 class int: pass
 class str: pass
 class bool: pass
+
+property = object() # Dummy definition.