ruff/crates/red_knot_python_semantic/resources/mdtest/annotations/deferred.md

Deferred annotations

Deferred annotations in stubs always resolve

mod.pyi:

def get_foo() -> Foo: ...
class Foo: ...

from mod import get_foo

reveal_type(get_foo())  # revealed: Foo

Deferred annotations in regular code fail

In (regular) source files, annotations are not deferred. This also tests that imports from __future__ that are not annotations are ignored.

from __future__ import with_statement as annotations

# error: [unresolved-reference]
def get_foo() -> Foo: ...

class Foo: ...

reveal_type(get_foo())  # revealed: Unknown

Deferred annotations in regular code with __future__.annotations

If __future__.annotations is imported, annotations are deferred.

from __future__ import annotations

def get_foo() -> Foo: ...

class Foo: ...

reveal_type(get_foo())  # revealed: Foo