Consider TypeVarTuple to be invariant (#16759)

The TypeVarTuple equality checks mentioned in PEP 646 assume
TypeVarTuple to be `invariant`.
https://peps.python.org/pep-0646/#type-variable-tuple-equality

Fixes: #16739

Author: cdce8p

mypy/constraints.py

@@ -894,8 +894,9 @@ def visit_instance(self, template: Instance) -> list[Constraint]:
                             res.append(Constraint(template_arg, SUBTYPE_OF, suffix))
                             res.append(Constraint(template_arg, SUPERTYPE_OF, suffix))
                     elif isinstance(tvar, TypeVarTupleType):
-                        # Handle variadic type variables covariantly for consistency.
-                        res.extend(infer_constraints(template_arg, mapped_arg, self.direction))
+                        # Consider variadic type variables to be invariant.
+                        res.extend(infer_constraints(template_arg, mapped_arg, SUBTYPE_OF))
+                        res.extend(infer_constraints(template_arg, mapped_arg, SUPERTYPE_OF))
                 return res
             if (
                 template.type.is_protocol

mypy/test/testconstraints.py

@@ -30,13 +30,18 @@ def test_basic_type_var_tuple_subtype(self) -> None:
 
     def test_basic_type_var_tuple(self) -> None:
         fx = self.fx
-        assert infer_constraints(
-            Instance(fx.gvi, [UnpackType(fx.ts)]), Instance(fx.gvi, [fx.a, fx.b]), SUPERTYPE_OF
-        ) == [
+        assert set(
+            infer_constraints(
+                Instance(fx.gvi, [UnpackType(fx.ts)]), Instance(fx.gvi, [fx.a, fx.b]), SUPERTYPE_OF
+            )
+        ) == {
             Constraint(
                 type_var=fx.ts, op=SUPERTYPE_OF, target=TupleType([fx.a, fx.b], fx.std_tuple)
-            )
-        ]
+            ),
+            Constraint(
+                type_var=fx.ts, op=SUBTYPE_OF, target=TupleType([fx.a, fx.b], fx.std_tuple)
+            ),
+        }
 
     def test_type_var_tuple_with_prefix_and_suffix(self) -> None:
         fx = self.fx
@@ -51,6 +56,9 @@ def test_type_var_tuple_with_prefix_and_suffix(self) -> None:
             Constraint(
                 type_var=fx.ts, op=SUPERTYPE_OF, target=TupleType([fx.b, fx.c], fx.std_tuple)
             ),
+            Constraint(
+                type_var=fx.ts, op=SUBTYPE_OF, target=TupleType([fx.b, fx.c], fx.std_tuple)
+            ),
             Constraint(type_var=fx.s, op=SUPERTYPE_OF, target=fx.d),
         }
 
@@ -64,7 +72,9 @@ def test_unpack_homogenous_tuple(self) -> None:
             )
         ) == {
             Constraint(type_var=fx.t, op=SUPERTYPE_OF, target=fx.a),
+            Constraint(type_var=fx.t, op=SUBTYPE_OF, target=fx.a),
             Constraint(type_var=fx.t, op=SUPERTYPE_OF, target=fx.b),
+            Constraint(type_var=fx.t, op=SUBTYPE_OF, target=fx.b),
         }
 
     def test_unpack_homogenous_tuple_with_prefix_and_suffix(self) -> None:
@@ -78,7 +88,9 @@ def test_unpack_homogenous_tuple_with_prefix_and_suffix(self) -> None:
         ) == {
             Constraint(type_var=fx.t, op=SUPERTYPE_OF, target=fx.a),
             Constraint(type_var=fx.s, op=SUPERTYPE_OF, target=fx.b),
+            Constraint(type_var=fx.s, op=SUBTYPE_OF, target=fx.b),
             Constraint(type_var=fx.s, op=SUPERTYPE_OF, target=fx.c),
+            Constraint(type_var=fx.s, op=SUBTYPE_OF, target=fx.c),
             Constraint(type_var=fx.u, op=SUPERTYPE_OF, target=fx.d),
         }
 
@@ -93,7 +105,9 @@ def test_unpack_with_prefix_and_suffix(self) -> None:
         ) == {
             Constraint(type_var=fx.u, op=SUPERTYPE_OF, target=fx.a),
             Constraint(type_var=fx.t, op=SUPERTYPE_OF, target=fx.b),
+            Constraint(type_var=fx.t, op=SUBTYPE_OF, target=fx.b),
             Constraint(type_var=fx.s, op=SUPERTYPE_OF, target=fx.c),
+            Constraint(type_var=fx.s, op=SUBTYPE_OF, target=fx.c),
             Constraint(type_var=fx.u, op=SUPERTYPE_OF, target=fx.d),
         }
 

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

@@ -2277,3 +2277,30 @@ higher_order(bad2)  # E: Argument 1 to "higher_order" has incompatible type "Cal
 higher_order(bad3)  # E: Argument 1 to "higher_order" has incompatible type "Callable[[NamedArg(str, 'd')], int]"; expected "Callable[[int, str, VarArg(Unpack[Tuple[Unpack[Tuple[Any, ...]], int]])], Any]"
 higher_order(bad4)  # E: Argument 1 to "higher_order" has incompatible type "Callable[[KwArg(None)], None]"; expected "Callable[[int, str, VarArg(Unpack[Tuple[Unpack[Tuple[Any, ...]], int]])], Any]"
 [builtins fixtures/tuple.pyi]
+
+[case testTypeVarTupleInvariant]
+from typing import Generic, Tuple
+from typing_extensions import Unpack, TypeVarTuple
+Ts = TypeVarTuple("Ts")
+
+class Array(Generic[Unpack[Ts]]): ...
+
+def pointwise_multiply(x: Array[Unpack[Ts]], y: Array[Unpack[Ts]]) -> Array[Unpack[Ts]]: ...
+
+def a1(x: Array[int], y: Array[str], z: Array[int, str]) -> None:
+    reveal_type(pointwise_multiply(x, x))  # N: Revealed type is "__main__.Array[builtins.int]"
+    reveal_type(pointwise_multiply(x, y))  # E: Cannot infer type argument 1 of "pointwise_multiply" \
+                                           # N: Revealed type is "__main__.Array[Unpack[builtins.tuple[Any, ...]]]"
+    reveal_type(pointwise_multiply(x, z))  # E: Cannot infer type argument 1 of "pointwise_multiply" \
+                                           # N: Revealed type is "__main__.Array[Unpack[builtins.tuple[Any, ...]]]"
+
+def func(x: Array[Unpack[Ts]], *args: Unpack[Ts]) -> Tuple[Unpack[Ts]]:
+    ...
+
+def a2(x: Array[int, str]) -> None:
+    reveal_type(func(x, 2, "Hello"))  # N: Revealed type is "Tuple[builtins.int, builtins.str]"
+    reveal_type(func(x, 2))           # E: Cannot infer type argument 1 of "func" \
+                                      # N: Revealed type is "builtins.tuple[Any, ...]"
+    reveal_type(func(x, 2, "Hello", True))   # E: Cannot infer type argument 1 of "func" \
+                                             # N: Revealed type is "builtins.tuple[Any, ...]"
+[builtins fixtures/tuple.pyi]