From bfc7a88ee6fdc45cf2f948636a484e632d9a4c00 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Mon, 10 Mar 2025 23:12:13 +0000
Subject: [PATCH] Fix crash for callable with *args and suffix against Any

---
 mypy/constraints.py                     |  5 ++++-
 mypy/types.py                           |  2 +-
 test-data/unit/check-typevar-tuple.test | 12 ++++++++++++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/mypy/constraints.py b/mypy/constraints.py
index d88b722aa1ce..e76f6cd639ad 100644
--- a/mypy/constraints.py
+++ b/mypy/constraints.py
@@ -53,6 +53,7 @@
     UnionType,
     UnpackType,
     find_unpack_in_list,
+    flatten_nested_tuples,
     get_proper_type,
     has_recursive_types,
     has_type_vars,
@@ -1347,7 +1348,9 @@ def visit_type_alias_type(self, template: TypeAliasType) -> list[Constraint]:
 
     def infer_against_any(self, types: Iterable[Type], any_type: AnyType) -> list[Constraint]:
         res: list[Constraint] = []
-        for t in types:
+        # Some items may be things like `*Tuple[*Ts, T]` for example from callable types with
+        # suffix after *arg, so flatten them.
+        for t in flatten_nested_tuples(types):
             if isinstance(t, UnpackType):
                 if isinstance(t.type, TypeVarTupleType):
                     res.append(Constraint(t.type, self.direction, any_type))
diff --git a/mypy/types.py b/mypy/types.py
index f9749945d9e9..9dd0ef8552b9 100644
--- a/mypy/types.py
+++ b/mypy/types.py
@@ -3726,7 +3726,7 @@ def find_unpack_in_list(items: Sequence[Type]) -> int | None:
     return unpack_index
 
 
-def flatten_nested_tuples(types: Sequence[Type]) -> list[Type]:
+def flatten_nested_tuples(types: Iterable[Type]) -> list[Type]:
     """Recursively flatten TupleTypes nested with Unpack.
 
     For example this will transform
diff --git a/test-data/unit/check-typevar-tuple.test b/test-data/unit/check-typevar-tuple.test
index 2cc84c8e6b15..57a96291b04a 100644
--- a/test-data/unit/check-typevar-tuple.test
+++ b/test-data/unit/check-typevar-tuple.test
@@ -2606,3 +2606,15 @@ def test(xs: tuple[Unpack[Ts]], xsi: tuple[int, Unpack[Ts]]) -> None:
     reveal_type(join(xsi, ai))  # N: Revealed type is "Tuple[builtins.int, Unpack[builtins.tuple[Any, ...]]]"
     reveal_type(join(ai, xsi))  # N: Revealed type is "Tuple[builtins.int, Unpack[builtins.tuple[Any, ...]]]"
 [builtins fixtures/tuple.pyi]
+
+[case testTypeVarTupleInferAgainstAnyCallableSuffix]
+from typing import Any, Callable, TypeVar, TypeVarTuple
+
+Ts = TypeVarTuple("Ts")
+R = TypeVar("R")
+def deco(func: Callable[[*Ts, int], R]) -> Callable[[*Ts], R]:
+    ...
+
+untyped: Any
+reveal_type(deco(untyped))  # N: Revealed type is "def (*Any) -> Any"
+[builtins fixtures/tuple.pyi]