Support self-types containing ParamSpec (#15903)

Fixes #14968
Fixes #13911

The fix is simple, as I predicted on Discord, we simply should use
`get_all_type_vars()` instead of `get_type_vars()` (that specifically
returns only `TypeVarType`). I also use this opportunity to tidy-up code
in `bind_self()`, it should be now more readable, and much faster
(especially when compiled with mypyc).

cc @A5rocks

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Author: ilevkivskyi

mypy/typeops.py

@@ -303,7 +303,7 @@ class B(A): pass
         return cast(F, func)
     self_param_type = get_proper_type(func.arg_types[0])
 
-    variables: Sequence[TypeVarLikeType] = []
+    variables: Sequence[TypeVarLikeType]
     if func.variables and supported_self_type(self_param_type):
         from mypy.infer import infer_type_arguments
 
@@ -312,46 +312,40 @@ class B(A): pass
             original_type = erase_to_bound(self_param_type)
         original_type = get_proper_type(original_type)
 
-        all_ids = func.type_var_ids()
+        # Find which of method type variables appear in the type of "self".
+        self_ids = {tv.id for tv in get_all_type_vars(self_param_type)}
+        self_vars = [tv for tv in func.variables if tv.id in self_ids]
+
+        # Solve for these type arguments using the actual class or instance type.
         typeargs = infer_type_arguments(
-            func.variables, self_param_type, original_type, is_supertype=True
+            self_vars, self_param_type, original_type, is_supertype=True
         )
         if (
             is_classmethod
-            # TODO: why do we need the extra guards here?
             and any(isinstance(get_proper_type(t), UninhabitedType) for t in typeargs)
             and isinstance(original_type, (Instance, TypeVarType, TupleType))
         ):
-            # In case we call a classmethod through an instance x, fallback to type(x)
+            # In case we call a classmethod through an instance x, fallback to type(x).
             typeargs = infer_type_arguments(
-                func.variables, self_param_type, TypeType(original_type), is_supertype=True
+                self_vars, self_param_type, TypeType(original_type), is_supertype=True
             )
 
-        ids = [tid for tid in all_ids if any(tid == t.id for t in get_type_vars(self_param_type))]
-
-        # Technically, some constrains might be unsolvable, make them <nothing>.
+        # Update the method signature with the solutions found.
+        # Technically, some constraints might be unsolvable, make them <nothing>.
         to_apply = [t if t is not None else UninhabitedType() for t in typeargs]
-
-        def expand(target: Type) -> Type:
-            return expand_type(target, {id: to_apply[all_ids.index(id)] for id in ids})
-
-        arg_types = [expand(x) for x in func.arg_types[1:]]
-        ret_type = expand(func.ret_type)
-        variables = [v for v in func.variables if v.id not in ids]
+        func = expand_type(func, {tv.id: arg for tv, arg in zip(self_vars, to_apply)})
+        variables = [v for v in func.variables if v not in self_vars]
     else:
-        arg_types = func.arg_types[1:]
-        ret_type = func.ret_type
         variables = func.variables
 
     original_type = get_proper_type(original_type)
     if isinstance(original_type, CallableType) and original_type.is_type_obj():
         original_type = TypeType.make_normalized(original_type.ret_type)
     res = func.copy_modified(
-        arg_types=arg_types,
+        arg_types=func.arg_types[1:],
         arg_kinds=func.arg_kinds[1:],
         arg_names=func.arg_names[1:],
         variables=variables,
-        ret_type=ret_type,
         bound_args=[original_type],
     )
     return cast(F, res)

test-data/unit/check-selftype.test

@@ -1973,3 +1973,45 @@ class B(A):
         reveal_type(self.x.extra)  # N: Revealed type is "builtins.int"
         reveal_type(self.xs[0].extra)  # N: Revealed type is "builtins.int"
 [builtins fixtures/list.pyi]
+
+[case testSelfTypesWithParamSpecExtract]
+from typing import Any, Callable, Generic, TypeVar
+from typing_extensions import ParamSpec
+
+P = ParamSpec("P")
+F = TypeVar("F", bound=Callable[..., Any])
+class Example(Generic[F]):
+    def __init__(self, fn: F) -> None:
+        ...
+    def __call__(self: Example[Callable[P, Any]], *args: P.args, **kwargs: P.kwargs) -> None:
+        ...
+
+def test_fn(a: int, b: str) -> None:
+    ...
+
+example = Example(test_fn)
+example()  # E: Missing positional arguments "a", "b" in call to "__call__" of "Example"
+example(1, "b")  # OK
+[builtins fixtures/list.pyi]
+
+[case testSelfTypesWithParamSpecInfer]
+from typing import TypeVar, Protocol, Type, Callable
+from typing_extensions import ParamSpec
+
+R = TypeVar("R", covariant=True)
+P = ParamSpec("P")
+class AsyncP(Protocol[P]):
+    def meth(self, *args: P.args, **kwargs: P.kwargs) -> None:
+        ...
+
+class Async:
+    @classmethod
+    def async_func(cls: Type[AsyncP[P]]) -> Callable[P, int]:
+        ...
+
+class Add(Async):
+    def meth(self, x: int, y: int) -> None: ...
+
+reveal_type(Add.async_func())  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+reveal_type(Add().async_func())  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+[builtins fixtures/classmethod.pyi]