Fix recursive type alias crash in make_simplified_union (#15216)

This is a recent regression
python · May 10, 2023 · fe7007f · fe7007f
1 parent 35acb1b
commit fe7007f
Show file tree

Hide file tree

Showing 2 changed files with 15 additions and 1 deletion.
diff --git a/mypy/typeops.py b/mypy/typeops.py
@@ -528,7 +528,7 @@ def _remove_redundant_union_items(items: list[Type], keep_erased: bool) -> list[
                         continue
 
                     if is_proper_subtype(
-                        proper_ti, tj, keep_erased_types=keep_erased, ignore_promotions=True
+                        ti, tj, keep_erased_types=keep_erased, ignore_promotions=True
                     ):
                         duplicate_index = j
                         break

diff --git a/test-data/unit/check-recursive-types.test b/test-data/unit/check-recursive-types.test
@@ -923,3 +923,17 @@ def dummy() -> None:
         pass
     reveal_type(bar)  # N: Revealed type is "def [T <: builtins.dict[builtins.str, builtins.dict[builtins.str, builtins.str]]] (x: T`-1) -> T`-1"
 [builtins fixtures/dict.pyi]
+
+[case testAliasRecursiveUnpackMultiple]
+from typing import Tuple, TypeVar, Optional
+
+T = TypeVar("T")
+S = TypeVar("S")
+
+A = Tuple[T, S, Optional[A[T, S]]]
+x: A[int, str]
+
+*_, last = x
+if last is not None:
+    reveal_type(last)  # N: Revealed type is "Tuple[builtins.int, builtins.str, Union[Tuple[builtins.int, builtins.str, Union[..., None]], None]]"
+[builtins fixtures/tuple.pyi]