Untyped functions content show up in mypy output

[rogalski]

Bug Report

For default configuration, violations can be reported in untyped (shouldn't be checked) functions.

To Reproduce

def f():
    return UNDEFINED


def g():
    return lambda x: UNDEFINED in x

https://mypy-play.net/?mypy=latest&python=3.10&gist=c49b86bc9067f234a038a71598d2b3b7

Expected Behavior

Both f() and g() are untyped - violations shouldn't be reported in any of those.

Actual Behavior

main.py:6: error: Name "UNDEFINED" is not defined

Your Environment

mypy-play, as linked above.

[sobolevn]

Good question!

We don't check unannotated functions without --check-untyped-defs option.
But, lambda is not considered to be unannotated, because it cannot be annotated due to Python syntax limitations.
So, lambda x: UNDEFINED in x is considered to be typed. That's why it is checked.

I also agree with its conclusion, UNDEFINED is not defined.
I guess I can update docs to mention this special case.

Related #10895 and #3948

[sobolevn]

@hauntsaninja any ideas about the best place for such docs?

[sobolevn]

I think that adding a new section here might be a good idea.

[sobolevn]

Another option for lambda is to inherit "annotated" status from its context:

• Not a function (module, class body) -> lambda is annotated
• Annotated function / method -> lambda is annotated
• Unannotated function / method -> lambda is not unnotated

[rogalski]

+1 for inheriting annotated status from enclosing scope.