don't consider self

Author: dcreager

crates/ty_python_semantic/resources/mdtest/type_properties/is_subtype_of.md

@@ -1963,6 +1963,10 @@ static_assert(not is_subtype_of(type[A], Callable[[int], A]))
 
 ### Bound methods
 
+The bound `self` or `cls` parameter of a bound method has been curried away, and is no longer
+available as a parameter when calling it. It therefore is not considered when checking subtyping
+involving the bound method.
+
 ```py
 from typing import Callable
 from ty_extensions import TypeOf, static_assert, is_subtype_of
@@ -1981,12 +1985,131 @@ static_assert(is_subtype_of(TypeOf[a.f], Callable[[int], int]))
 static_assert(is_subtype_of(TypeOf[a.g], Callable[[int], int]))
 static_assert(is_subtype_of(TypeOf[A.g], Callable[[int], int]))
 
-static_assert(not is_subtype_of(TypeOf[a.f], Callable[[float], int]))
 static_assert(not is_subtype_of(TypeOf[A.g], Callable[[], int]))
 
 static_assert(is_subtype_of(TypeOf[A.f], Callable[[A, int], int]))
 ```
 
+Return types are in covariant position:
+
+```py
+static_assert(is_subtype_of(TypeOf[a.f], Callable[[int], object]))
+static_assert(is_subtype_of(TypeOf[a.g], Callable[[int], object]))
+static_assert(is_subtype_of(TypeOf[A.g], Callable[[int], object]))
+
+static_assert(not is_subtype_of(TypeOf[a.f], Callable[[int], bool]))
+static_assert(not is_subtype_of(TypeOf[a.g], Callable[[int], bool]))
+static_assert(not is_subtype_of(TypeOf[A.g], Callable[[int], bool]))
+```
+
+Parameter types are in contravariant position:
+
+```py
+static_assert(not is_subtype_of(TypeOf[a.f], Callable[[object], int]))
+static_assert(not is_subtype_of(TypeOf[a.g], Callable[[object], int]))
+static_assert(not is_subtype_of(TypeOf[A.g], Callable[[object], int]))
+
+static_assert(is_subtype_of(TypeOf[a.f], Callable[[bool], int]))
+static_assert(is_subtype_of(TypeOf[a.g], Callable[[bool], int]))
+static_assert(is_subtype_of(TypeOf[A.g], Callable[[bool], int]))
+```
+
+We should get the same results when comparing with a bound method of a different class.
+
+```py
+class B:
+    def returns_int(self, a: int) -> int:
+        return 0
+
+    def returns_object(self, a: int) -> object:
+        return a
+
+    def returns_bool(self, a: int) -> bool:
+        return True
+
+    def takes_object(self, a: object) -> int:
+        return 0
+
+    def takes_bool(self, a: bool) -> int:
+        return 0
+
+    @classmethod
+    def class_returns_int(cls, a: int) -> int:
+        return 0
+
+    @classmethod
+    def class_returns_object(cls, a: int) -> object:
+        return a
+
+    @classmethod
+    def class_returns_bool(cls, a: int) -> bool:
+        return True
+
+    @classmethod
+    def class_takes_object(cls, a: object) -> int:
+        return 0
+
+    @classmethod
+    def class_takes_bool(cls, a: bool) -> int:
+        return 0
+
+b = B()
+
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[b.returns_object]))
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[b.returns_int]))
+static_assert(not is_subtype_of(TypeOf[a.f], TypeOf[b.returns_bool]))
+static_assert(not is_subtype_of(TypeOf[a.f], TypeOf[b.takes_object]))
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[b.takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[b.class_returns_object]))
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[b.class_returns_int]))
+static_assert(not is_subtype_of(TypeOf[a.f], TypeOf[b.class_returns_bool]))
+static_assert(not is_subtype_of(TypeOf[a.f], TypeOf[b.class_takes_object]))
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[b.class_takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[B.class_returns_object]))
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[B.class_returns_int]))
+static_assert(not is_subtype_of(TypeOf[a.f], TypeOf[B.class_returns_bool]))
+static_assert(not is_subtype_of(TypeOf[a.f], TypeOf[B.class_takes_object]))
+static_assert(is_subtype_of(TypeOf[a.f], TypeOf[B.class_takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[b.returns_object]))
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[b.returns_int]))
+static_assert(not is_subtype_of(TypeOf[a.g], TypeOf[b.returns_bool]))
+static_assert(not is_subtype_of(TypeOf[a.g], TypeOf[b.takes_object]))
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[b.takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[b.class_returns_object]))
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[b.class_returns_int]))
+static_assert(not is_subtype_of(TypeOf[a.g], TypeOf[b.class_returns_bool]))
+static_assert(not is_subtype_of(TypeOf[a.g], TypeOf[b.class_takes_object]))
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[b.class_takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[B.class_returns_object]))
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[B.class_returns_int]))
+static_assert(not is_subtype_of(TypeOf[a.g], TypeOf[B.class_returns_bool]))
+static_assert(not is_subtype_of(TypeOf[a.g], TypeOf[B.class_takes_object]))
+static_assert(is_subtype_of(TypeOf[a.g], TypeOf[B.class_takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[b.returns_object]))
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[b.returns_int]))
+static_assert(not is_subtype_of(TypeOf[A.g], TypeOf[b.returns_bool]))
+static_assert(not is_subtype_of(TypeOf[A.g], TypeOf[b.takes_object]))
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[b.takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[b.class_returns_object]))
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[b.class_returns_int]))
+static_assert(not is_subtype_of(TypeOf[A.g], TypeOf[b.class_returns_bool]))
+static_assert(not is_subtype_of(TypeOf[A.g], TypeOf[b.class_takes_object]))
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[b.class_takes_bool]))
+
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[B.class_returns_object]))
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[B.class_returns_int]))
+static_assert(not is_subtype_of(TypeOf[A.g], TypeOf[B.class_returns_bool]))
+static_assert(not is_subtype_of(TypeOf[A.g], TypeOf[B.class_takes_object]))
+static_assert(is_subtype_of(TypeOf[A.g], TypeOf[B.class_takes_bool]))
+```
+
 ### Overloads
 
 #### Subtype overloaded

crates/ty_python_semantic/src/types.rs

@@ -9165,20 +9165,16 @@ impl<'db> BoundMethodType<'db> {
         relation: TypeRelation,
         visitor: &HasRelationToVisitor<'db>,
     ) -> ConstraintSet<'db> {
-        // A bound method is a typically a subtype of itself. However, we must explicitly verify
-        // the subtyping of the underlying function signatures (since they might be specialized
-        // differently), and of the bound self parameter (taking care that parameters, including a
-        // bound self parameter, are contravariant.)
-        self.function(db)
-            .has_relation_to_impl(db, other.function(db), relation, visitor)
-            .and(db, || {
-                other.self_instance(db).has_relation_to_impl(
-                    db,
-                    self.self_instance(db),
-                    relation,
-                    visitor,
-                )
-            })
+        // Note that we do not consider `self_instance`, and we use `into_callable_type` to compare
+        // the signatures of the bound methods _after_ the `self` parameter has been bound. The
+        // bound `self` is no longer available as a parameter to callers, and should therefore not
+        // influence the result of the check.
+        self.into_callable_type(db).has_relation_to_impl(
+            db,
+            other.into_callable_type(db),
+            relation,
+            visitor,
+        )
     }
 
     fn is_equivalent_to_impl(
@@ -9187,13 +9183,12 @@ impl<'db> BoundMethodType<'db> {
         other: Self,
         visitor: &IsEquivalentVisitor<'db>,
     ) -> ConstraintSet<'db> {
-        self.function(db)
-            .is_equivalent_to_impl(db, other.function(db), visitor)
-            .and(db, || {
-                other
-                    .self_instance(db)
-                    .is_equivalent_to_impl(db, self.self_instance(db), visitor)
-            })
+        // Note that we do not consider `self_instance`, and we use `into_callable_type` to compare
+        // the signatures of the bound methods _after_ the `self` parameter has been bound. The
+        // bound `self` is no longer available as a parameter to callers, and should therefore not
+        // influence the result of the check.
+        self.into_callable_type(db)
+            .is_equivalent_to_impl(db, other.into_callable_type(db), visitor)
     }
 }