Incorrect use of Any in second occurrence of type in signature

[wilcoxjay]

Consider the following code.

from __future__ import annotations
from typing import Optional

class C1(object):
    def foo(self, a: C, b: C) -> None:
        reveal_type(a)  # Optional[C1]
        reveal_type(b)  # Any

    def bar(self, a: C) -> C:
        reveal_type(a)  # Optional[C1]
        return a

    def baz(self) -> C:
        return C()

C = Optional[C1]
        
def main() -> None:
    reveal_type(C1().foo)  # def (a: Optional[C1], b: Any)
    reveal_type(C1().bar)  # def (a: Optional[C1]) -> Any
    reveal_type(C1().baz)  # def () -> Optional[C1]

Note that C is defined after the class body of C1, but C is used in several type annotations in the body of C1 (taking advantage of from __future__ import annotations).

In each method of C1, the first occurrence of C is correctly used by mypy, but subsequent occurrences (in later parameter types or the return type) are incorrectly interpreted as Any.

If I move the alias definition C = Optional[C1] above the class body (and fix the resulting forward reference using a string), then everything works.

If this is the expected behavior, then consider this issue a request for a better error message than silently inferring Any.

I observe this behavior both on mypy version 0.650 and on the most recent master (01c268644).

[ilevkivskyi]

Thanks for reporting! This is definitely a bug.

Note there is a similar issue #5842. Maybe this problem is somehow related to deferred nodes?

[ilevkivskyi]

This now works correctly, I get:

tstdefer.py:6: note: Revealed type is "Union[tstdefer.C1, None]"
tstdefer.py:7: note: Revealed type is "Union[tstdefer.C1, None]"
tstdefer.py:10: note: Revealed type is "Union[tstdefer.C1, None]"
tstdefer.py:14: error: "<typing special form>" not callable  [operator]
tstdefer.py:19: note: Revealed type is "def (a: Union[tstdefer.C1, None], b: Union[tstdefer.C1, None])"
tstdefer.py:20: note: Revealed type is "def (a: Union[tstdefer.C1, None]) -> Union[tstdefer.C1, None]"
tstdefer.py:21: note: Revealed type is "def () -> Union[tstdefer.C1, None]"