Note that assert_type always matches against any in untyped function

[rsokl]

Description

reveal_type provides a useful note to users that it will always reveal Any within an unchecked function. Similarly, assert_type always checks against Any, but does not notify the user about its behavior.

This PR adds said note, which is displayed when assert_type raises an error in an unchecked function

Test Plan

I added a test to test-data/unit/check-expressions.test that is comparable to the corresponding test case for reveal_type in an unchecked scope.

[JelleZijlstra]

I don't think this is quite right; assert_type() doesn't output anything.

[rsokl]

Ah, you mean in terms of wording? Would this be better? "assert_type(x, y) always evaluates x as Any in unchecked functions"

[rsokl]

Oh, I see now.. if doesn't actually output a message in the test.

When I actually run it from my branch I saw

$ mypy func_scope.py 
func_scope.py:5: error: Expression is of type "Any", not "Literal[42]"
func_scope.py:5: note: 'assert_type' always outputs 'Any' in unchecked functions
Found 1 error in 1 file (checked 1 source file)

so it had looked like my fix worked

[JelleZijlstra]

Yes, your code looks correct in the sense that the note gets output, but I don't think the wording is good. I like @hauntsaninja's suggestion below.

[rsokl]

Gotchya!

I am not sure why my test is failing. It looks like it has the same form as the other test cases, but no message is emitted: https://github.com/python/mypy/runs/8241823231?check_suite_focus=true#step:8:295

[hauntsaninja]

You need to make sure [builtins fixtures/tuple.pyi] follows the body of the test (this is why your change regresses the previous test). I believe you also need to import assert_type from typing; mypy doesn't pretend it exists in builtins like with reveal_type

[rsokl]

You need to make sure [builtins fixtures/tuple.pyi]

Got it! I updated the note and fixed the test according to your feedback

[rsokl]

Thanks @sobolevn I addressed your comments in d25a8e1

[rsokl]

I think that this can be affected by https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-check-untyped-defs

@sobolevn you are right: including --check-untyped-defs` does affect this behavior. The test case that you recommended demonstrates this: https://github.com/python/mypy/runs/8254912870?check_suite_focus=true

I am beyond my depth with working with mypy's internals here, and am afraid that I am wasting mypy dev time by stumbling my way through this. I am happy to close this if it is easier for someone else to take care of this.

[sobolevn]

@rsokl no worries, I am happy to help :)
The first PR is the most important one!

My understanding is that self.chk.in_checked_function() takes --check-untyped-defs into account. So, the test with this option should not raise this warning.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[sobolevn]

LGMT, any other comments? :)

[hauntsaninja]

Thank you!

[rsokl]

Thank you, all of you, for your help! I really appreciate it