Correctly handle empty tuple index when unpacked

mypy/typeanal.py

@@ -884,7 +884,10 @@ def analyze_type_with_type_info(
             return AnyType(TypeOfAny.from_error)
 
         # Check type argument count.
+        old_args = instance.args
         instance.args = tuple(flatten_nested_tuples(instance.args))
+        if old_args and not instance.args:
+            empty_tuple_index = True
         if not (self.defining_alias and self.nesting_level == 0) and not validate_instance(
             instance, self.fail, empty_tuple_index
         ):
@@ -2192,7 +2195,10 @@ def instantiate_type_alias(
     # Type aliases are special, since they can be expanded during semantic analysis,
     # so we need to normalize them as soon as possible.
     # TODO: can this cause an infinite recursion?
+    old_args = args
     args = flatten_nested_tuples(args)
+    if old_args and not args:
+        empty_tuple_index = True
     if any(unknown_unpack(a) for a in args):
         # This type is not ready to be validated, because of unknown total count.
         # Note that we keep the kind of Any for consistency.

test-data/unit/check-python313.test

@@ -451,3 +451,32 @@ reveal_type(a)  # N: Revealed type is "builtins.list[builtins.list[Any]]"
 type A[T = A] = int
 a: A
 reveal_type(a)  # N: Revealed type is "builtins.int"
+
+[case testPEP695VariadicGenericClassEmptyTupleUnpackIndex]
+class Blah[*Ts]:
+    pass
+
+x: Blah[()]
+y: Blah[*tuple[()]]
+
+type Empty = tuple[()]
+z: Blah[*Empty]
+
+reveal_type(x)  # N: Revealed type is "__main__.Blah[()]"
+reveal_type(y)  # N: Revealed type is "__main__.Blah[()]"
+reveal_type(z)  # N: Revealed type is "__main__.Blah[()]"
+[builtins fixtures/tuple.pyi]
+
+[case testPEP695VariadicGenericAliasEmptyTupleUnpackIndex]
+type Blah[*Ts] = list[tuple[*Ts]]
+
+x: Blah[()]
+y: Blah[*tuple[()]]
+
+type Empty = tuple[()]
+z: Blah[*Empty]
+
+reveal_type(x)  # N: Revealed type is "builtins.list[tuple[()]]"
+reveal_type(y)  # N: Revealed type is "builtins.list[tuple[()]]"
+reveal_type(z)  # N: Revealed type is "builtins.list[tuple[()]]"
+[builtins fixtures/tuple.pyi]

test-data/unit/check-typevar-tuple.test

@@ -2838,3 +2838,38 @@ def test(t: tuple[int, ...]) -> None: ...
 test(x)
 test(y)
 [builtins fixtures/tuple.pyi]
+
+[case testVariadicGenericClassEmptyTupleUnpackIndex]
+from typing import Generic, TypeVarTuple, Unpack
+
+Ts = TypeVarTuple("Ts")
+class Blah(Generic[Unpack[Ts]]):
+    pass
+
+x: Blah[()]
+y: Blah[Unpack[tuple[()]]]
+
+Empty = tuple[()]
+z: Blah[Unpack[Empty]]
+
+reveal_type(x)  # N: Revealed type is "__main__.Blah[()]"
+reveal_type(y)  # N: Revealed type is "__main__.Blah[()]"
+reveal_type(z)  # N: Revealed type is "__main__.Blah[()]"
+[builtins fixtures/tuple.pyi]
+
+[case testVariadicGenericAliasEmptyTupleUnpackIndex]
+from typing import Generic, TypeVarTuple, Unpack
+
+Ts = TypeVarTuple("Ts")
+Blah = list[tuple[Unpack[Ts]]]
+
+x: Blah[()]
+y: Blah[Unpack[tuple[()]]]
+
+Empty = tuple[()]
+z: Blah[Unpack[Empty]]
+
+reveal_type(x)  # N: Revealed type is "builtins.list[tuple[()]]"
+reveal_type(y)  # N: Revealed type is "builtins.list[tuple[()]]"
+reveal_type(z)  # N: Revealed type is "builtins.list[tuple[()]]"
+[builtins fixtures/tuple.pyi]