Handle another edge case

Author: ilevkivskyi

mypy/binder.py

@@ -318,7 +318,10 @@ def update_from_options(self, frames: list[Frame]) -> bool:
             # variable types to be widened using subsequent assignments. This is
             # tricky to support for instance attributes (primarily due to deferrals),
             # so we don't use it for them.
-            old_semantics = not self.bind_all or extract_var_from_literal_hash(key) is None
+            var = extract_var_from_literal_hash(key)
+            old_semantics = (
+                not self.bind_all or var is None or not var.is_inferred and not var.is_argument
+            )
             if old_semantics and any(x is None for x in resulting_values):
                 # We didn't know anything about key before
                 # (current_value must be None), and we still don't

mypy/checker.py

@@ -3427,6 +3427,9 @@ def check_assignment(
                     self.options.allow_redefinition_new
                     and lvalue_type is not None
                     and not isinstance(lvalue_type, PartialType)
+                    and isinstance(lvalue, NameExpr)
+                    and isinstance(lvalue.node, Var)
+                    and lvalue.node.is_inferred
                 ):
                     # TODO: Can we use put() here?
                     self.binder.assign_type(lvalue, lvalue_type, lvalue_type)

test-data/unit/check-redefine2.test

@@ -69,7 +69,7 @@ def f1() -> None:
         x: Union[int, str] = 0
         reveal_type(x) # N: Revealed type is "builtins.int | builtins.str"
         x = ""
-    reveal_type(x) # N: Revealed type is "builtins.str"
+    reveal_type(x) # N: Revealed type is "builtins.int | builtins.str"
 
 [case testNewRedefineUninitializedCodePath3]
 # flags: --allow-redefinition-new --local-partial-types
@@ -1378,3 +1378,20 @@ async def test(x: Optional[str]) -> None:
     if x is None:
         x = await gen("foo")
     reveal_type(x)  # N: Revealed type is "builtins.str"
+
+[case testNewRedefineNarrowingOnFirstAssignment]
+# flags: --allow-redefinition-new --local-partial-types
+from typing import Any
+
+li: list[int]
+
+def test() -> None:
+    x: list[Any] = li
+    reveal_type(x)  # N: Revealed type is "builtins.list[Any]"
+
+    if bool():
+        y: list[Any] = li
+    else:
+        y = li
+    reveal_type(y)  # N: Revealed type is "builtins.list[Any]"
+[builtins fixtures/primitives.pyi]