Support properties with generic setters (#19298)

This is yet another followup for `checkmember` work.

This handles a niche use case, but it is still used in the wild, and
this restores parity between logic for descriptors with `__set__()` and
properties with custom setters.

Author: ilevkivskyi

mypy/checkmember.py

@@ -968,7 +968,13 @@ def expand_and_bind_callable(
     # TODO: a decorated property can result in Overloaded here.
     assert isinstance(expanded, CallableType)
     if var.is_settable_property and mx.is_lvalue and var.setter_type is not None:
-        # TODO: use check_call() to infer better type, same as for __set__().
+        if expanded.variables:
+            type_ctx = mx.rvalue or TempNode(AnyType(TypeOfAny.special_form), context=mx.context)
+            _, inferred_expanded = mx.chk.expr_checker.check_call(
+                expanded, [type_ctx], [ARG_POS], mx.context
+            )
+            expanded = get_proper_type(inferred_expanded)
+            assert isinstance(expanded, CallableType)
         if not expanded.arg_types:
             # This can happen when accessing invalid property from its own body,
             # error will be reported elsewhere.

test-data/unit/check-generics.test

@@ -3628,3 +3628,32 @@ def draw_none(
         takes_int_str_none(c2)
         takes_int_str_none(c3)
 [builtins fixtures/tuple.pyi]
+
+[case testPropertyWithGenericSetter]
+from typing import TypeVar
+
+class B: ...
+class C(B): ...
+T = TypeVar("T", bound=B)
+
+class Test:
+    @property
+    def foo(self) -> list[C]: ...
+    @foo.setter
+    def foo(self, val: list[T]) -> None: ...
+
+t1: Test
+t2: Test
+
+lb: list[B]
+lc: list[C]
+li: list[int]
+
+t1.foo = lb
+t1.foo = lc
+t1.foo = li  # E: Value of type variable "T" of "foo" of "Test" cannot be "int"
+
+t2.foo = [B()]
+t2.foo = [C()]
+t2.foo = [1]  # E: Value of type variable "T" of "foo" of "Test" cannot be "int"
+[builtins fixtures/property.pyi]