Do not push partial types to binder

Author: sterliakov

mypy/checker.py

@@ -3311,6 +3311,7 @@ def check_assignment(
                                 # Partial type can't be final, so strip any literal values.
                                 rvalue_type = remove_instance_last_known_values(rvalue_type)
                                 inferred_type = make_simplified_union([rvalue_type, NoneType()])
+                                self.binder.put(lvalue, inferred_type)
                                 self.set_inferred_type(var, lvalue, inferred_type)
                             else:
                                 var.type = None
@@ -3373,6 +3374,7 @@ def check_assignment(
                                 break
                         if has_if_ancestor:
                             lvalue_type = make_optional_type(lvalue_type)
+                            self.binder.put(lvalue, lvalue_type)
                             self.set_inferred_type(lvalue.node, lvalue, lvalue_type)
 
                     rvalue_type, lvalue_type = self.check_simple_assignment(
@@ -3413,7 +3415,11 @@ def check_assignment(
                             and lvalue_type is not None
                         ):
                             lvalue.node.type = remove_instance_last_known_values(lvalue_type)
-                elif self.options.allow_redefinition_new and lvalue_type is not None:
+                elif (
+                    self.options.allow_redefinition_new
+                    and lvalue_type is not None
+                    and not isinstance(lvalue_type, PartialType)
+                ):
                     # TODO: Can we use put() here?
                     self.binder.assign_type(lvalue, lvalue_type, lvalue_type)
 

test-data/unit/check-redefine2.test

@@ -369,6 +369,16 @@ class C4:
         reveal_type(self.x) # N: Revealed type is "builtins.list[builtins.str]"
 
 reveal_type(C4().x) # N: Revealed type is "builtins.list[builtins.str]"
+
+class C5:
+    def __init__(self) -> None:
+        if int():
+            self.x = None
+            return
+        self.x = [""]
+        reveal_type(self.x) # N: Revealed type is "builtins.list[builtins.str]"
+
+reveal_type(C5().x) # N: Revealed type is "Union[builtins.list[builtins.str], None]"
 [builtins fixtures/list.pyi]
 
 [case testNewRedefinePartialGenericTypes]