Fix #2998: correctly handle MemberExpr in infer_partial_type

Author: refi64

mypy/checker.py

@@ -1608,7 +1608,7 @@ 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

@@ -1272,6 +1272,20 @@ class A:
 [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]
+
 [case testInferSetInitializedToEmpty]
 a = set()
 a.add(1)

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.