Fix type inference regression

python · JukkaL · Dec 6, 2019 · Dec 5, 2019 · Dec 5, 2019 · Dec 6, 2019
commit 268092fa4b6c2a110b968277ce66e9003709b1a8
diff --git a/mypy/checker.py b/mypy/checker.py
@@ -2174,7 +2174,7 @@ def try_infer_partial_generic_type_from_assignment(self,
             rvalue_type = get_proper_type(rvalue_type)
             if isinstance(rvalue_type, Instance):
                 if rvalue_type.type == typ.type:
-                    var.type = rvalue_type
+                    self.infer_variable_type(var, lvalue, rvalue_type, rvalue)
                     del partial_types[var]
             elif isinstance(rvalue_type, AnyType):
                 var.type = fill_typevars_with_any(typ.type)

diff --git a/test-data/unit/check-inference.test b/test-data/unit/check-inference.test
@@ -1585,6 +1585,17 @@ oo.update(d)
 reveal_type(oo) # N: Revealed type is 'collections.OrderedDict[builtins.int*, builtins.str*]'
 [builtins fixtures/dict.pyi]
 
+[case testEmptyCollectionAssignedToVariableTwice]
+x = [] # E: Need type annotation for 'x' (hint: "x: List[<type>] = ...")
+y = x
+x = []
+reveal_type(x) # N: Revealed type is 'builtins.list[Any]'
+d = {} # E: Need type annotation for 'd' (hint: "d: Dict[<type>, <type>] = ...")
+z = d
+d = {}
+reveal_type(d) # N: Revealed type is 'builtins.dict[Any, Any]'
+[builtins fixtures/dict.pyi]
+
 [case testInferAttributeInitializedToEmptyAndAssigned]
 class C:
     def __init__(self) -> None: