mirror of https://github.com/astral-sh/ruff.git synced 2025-09-28 21:05:08 +00:00

Douglas Creager f301931159

[ty] Induct into instances and subclasses when finding and applying generics (#18052 )

We were not inducting into instance types and subclass-of types when
looking for legacy typevars, nor when apply specializations.

This addresses
https://github.com/astral-sh/ruff/pull/17832#discussion_r2081502056

```py
from __future__ import annotations
from typing import TypeVar, Any, reveal_type

S = TypeVar("S")

class Foo[T]:
    def method(self, other: Foo[S]) -> Foo[T | S]: ...  # type: ignore[invalid-return-type]

def f(x: Foo[Any], y: Foo[Any]):
    reveal_type(x.method(y))  # revealed: `Foo[Any | S]`, but should be `Foo[Any]`
```

We were not detecting that `S` made `method` generic, since we were not
finding it when searching the function signature for legacy typevars.

2025-05-12 21:53:11 -04:00

4.1 KiB

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Self

Self is treated as if it were a TypeVar bound to the class it's being used on.

typing.Self is only available in Python 3.11 and later.

Methods

[environment]
python-version = "3.11"

from typing import Self

class Shape:
    def set_scale(self: Self, scale: float) -> Self:
        reveal_type(self)  # revealed: Self
        return self

    def nested_type(self: Self) -> list[Self]:
        return [self]

    def nested_func(self: Self) -> Self:
        def inner() -> Self:
            reveal_type(self)  # revealed: Self
            return self
        return inner()

    def implicit_self(self) -> Self:
        # TODO: first argument in a method should be considered as "typing.Self"
        reveal_type(self)  # revealed: Unknown
        return self

reveal_type(Shape().nested_type())  # revealed: list[Shape]
reveal_type(Shape().nested_func())  # revealed: Shape

class Circle(Shape):
    def set_scale(self: Self, scale: float) -> Self:
        reveal_type(self)  # revealed: Self
        return self

class Outer:
    class Inner:
        def foo(self: Self) -> Self:
            reveal_type(self)  # revealed: Self
            return self

typing_extensions

[environment]
python-version = "3.10"

from typing_extensions import Self

class C:
    def method(self: Self) -> Self:
        return self

reveal_type(C().method())  # revealed: C

Class Methods

[environment]
python-version = "3.11"

from typing import Self, TypeVar

class Shape:
    def foo(self: Self) -> Self:
        return self

    @classmethod
    def bar(cls: type[Self]) -> Self:
        # TODO: type[Shape]
        reveal_type(cls)  # revealed: @Todo(unsupported type[X] special form)
        return cls()

class Circle(Shape): ...

reveal_type(Shape().foo())  # revealed: Shape
# TODO: Shape
reveal_type(Shape.bar())  # revealed: Unknown

Attributes

[environment]
python-version = "3.11"

from typing import Self

class LinkedList:
    value: int
    next_node: Self

    def next(self: Self) -> Self:
        reveal_type(self.value)  # revealed: int
        return self.next_node

reveal_type(LinkedList().next())  # revealed: LinkedList

Generic Classes

[environment]
python-version = "3.11"

from typing import Self, Generic, TypeVar

T = TypeVar("T")

class Container(Generic[T]):
    value: T
    def set_value(self: Self, value: T) -> Self:
        return self

int_container: Container[int] = Container[int]()
reveal_type(int_container)  # revealed: Container[int]
reveal_type(int_container.set_value(1))  # revealed: Container[int]

Protocols

TODO: https://typing.python.org/en/latest/spec/generics.html#use-in-protocols

Annotations

[environment]
python-version = "3.11"

from typing import Self

class Shape:
    def union(self: Self, other: Self | None):
        reveal_type(other)  # revealed: Self | None
        return self

Invalid Usage

Self cannot be used in the signature of a function or variable.

[environment]
python-version = "3.11"

from typing import Self, Generic, TypeVar

T = TypeVar("T")

# error: [invalid-type-form]
def x(s: Self): ...

# error: [invalid-type-form]
b: Self

# TODO: "Self" cannot be used in a function with a `self` or `cls` parameter that has a type annotation other than "Self"
class Foo:
    # TODO: rejected Self because self has a different type
    def has_existing_self_annotation(self: T) -> Self:
        return self  # error: [invalid-return-type]

    def return_concrete_type(self) -> Self:
        # TODO: tell user to use "Foo" instead of "Self"
        # error: [invalid-return-type]
        return Foo()

    @staticmethod
    # TODO: reject because of staticmethod
    def make() -> Self:
        # error: [invalid-return-type]
        return Foo()

class Bar(Generic[T]):
    foo: T
    def bar(self) -> T:
        return self.foo

# error: [invalid-type-form]
class Baz(Bar[Self]): ...

class MyMetaclass(type):
    # TODO: rejected
    def __new__(cls) -> Self:
        return super().__new__(cls)

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