[Regression: 0.470->0.501] Lots of new errors relating to "uninhabited" in Django-based app code

[inducer]

git clone https://github.com/inducer/relate
cd relate
./run-mypy.sh

used to work with no warnings in 0.470. Now, it spews this:

course/content.py:877: error: <uninhabited> has no attribute "id"
course/content.py:1445: error: <uninhabited> has no attribute "preview_git_commit_sha"
course/content.py:1446: error: <uninhabited> has no attribute "preview_git_commit_sha"
course/utils.py:179: error: <uninhabited> has no attribute "exam"
course/utils.py:533: error: <uninhabited> has no attribute "preview_git_commit_sha"
course/utils.py:534: error: <uninhabited> has no attribute "preview_git_commit_sha"
course/utils.py:583: error: <uninhabited> has no attribute "permissions"
course/enrollment.py:129: error: <uninhabited> has no attribute "roles"
course/enrollment.py:143: error: <uninhabited> has no attribute "permissions"
course/views.py:156: error: <uninhabited> has no attribute "has_permission"
course/flow.py:416: error: <uninhabited> has no attribute "user"
course/flow.py:633: error: <uninhabited> has no attribute "answer"
course/flow.py:830: error: <uninhabited> has no attribute "get_most_recent_grade"
course/flow.py:848: error: Unsupported left operand type for + (some union)
course/flow.py:855: error: Unsupported left operand type for + (some union)
course/flow.py:862: error: Unsupported left operand type for + (some union)
course/flow.py:923: error: <uninhabited> has no attribute "is_submitted_answer"
course/flow.py:924: error: <uninhabited> has no attribute "save"
course/flow.py:1264: error: <uninhabited> has no attribute "get_most_recent_grade"

Focusing on the first error:

https://github.com/inducer/relate/blob/fed97182f4e8940bb032a224c5cbcd007a8bd722/course/content.py#L877

it should be clear that course is an instance of Course (i.e. not None).

[gvanrossum]

Yeah, I can repro this. @ddfisher The script uses --strict-optional.

I experimented with that one location a bit, and found:

• If you replace if course is not None ... with if course ... the error goes away.
• Without that change, reveal_type(course) inside the if shows <uninhabited>; with that change it shows Course.
• Either way, before the if, reveal_type(course) shows Optional[Course].

Definitely sounds like a binder issue...

[gvanrossum]

@inducer If you want to help, maybe you can use git bisect to track down the exact mypy commit that caused this?

[inducer]

Would love to, but paper deadline and 12 proposals to review over the next 7 days... Sorry!

[refi64]

Under mypy 0.47, I still get:

course/flow.py:1884: error: Call to untyped function "make_form" in typed context
course/flow.py:1943: error: Call to untyped function "form_to_html" in typed context
course/grading.py:189: error: Call to untyped function "make_form" in typed context
course/grading.py:206: error: Call to untyped function "form_to_html" in typed context
course/grading.py:229: error: Call to untyped function "update_grade_data_from_grading_form_v2" in typed context

[refi64]

Looks like some of the errors were caused by 9496d6f; I'm still trying to locate the others.

[refi64]

Oof, this one's a mess...more of the errors were from 9406886, but there are still some that haven't come up yet...

[refi64]

Around half of the errors were from, bizarrely enough, 3cc5201.

So, to sum it up:

• 9496d6f started the trouble:

  course/content.py:1445: error: object has no attribute "preview_git_commit_sha"
  course/content.py:1446: error: object has no attribute "preview_git_commit_sha"
  course/utils.py:533: error: object has no attribute "preview_git_commit_sha"
  course/utils.py:534: error: object has no attribute "preview_git_commit_sha"
  course/utils.py:583: error: object has no attribute "permissions"
  course/enrollment.py:129: error: object has no attribute "roles"
  course/views.py:156: error: object has no attribute "has_permission"
  course/flow.py:1264: error: object has no attribute "get_most_recent_grade"
  

• 9406886 changed the objects to <uninhabited>:

  course/content.py:1445: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/content.py:1446: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/utils.py:533: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/utils.py:534: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/utils.py:583: error: <uninhabited> has no attribute "permissions"
  course/enrollment.py:129: error: <uninhabited> has no attribute "roles"
  course/views.py:156: error: <uninhabited> has no attribute "has_permission"
  course/flow.py:1264: error: <uninhabited> has no attribute "get_most_recent_grade"
  

• 3cc5201 somehow just made it all worse:

  course/content.py:877: error: <uninhabited> has no attribute "id"
  course/content.py:1445: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/content.py:1446: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/utils.py:179: error: <uninhabited> has no attribute "exam"
  course/utils.py:533: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/utils.py:534: error: <uninhabited> has no attribute "preview_git_commit_sha"
  course/utils.py:583: error: <uninhabited> has no attribute "permissions"
  course/enrollment.py:129: error: <uninhabited> has no attribute "roles"
  course/enrollment.py:143: error: <uninhabited> has no attribute "permissions"
  course/views.py:156: error: <uninhabited> has no attribute "has_permission"
  course/flow.py:416: error: <uninhabited> has no attribute "user"
  course/flow.py:633: error: <uninhabited> has no attribute "answer"
  course/flow.py:830: error: <uninhabited> has no attribute "get_most_recent_grade"
  course/flow.py:848: error: Unsupported left operand type for + (some union)
  course/flow.py:855: error: Unsupported left operand type for + (some union)
  course/flow.py:862: error: Unsupported left operand type for + (some union)
  course/flow.py:923: error: <uninhabited> has no attribute "is_submitted_answer"
  course/flow.py:924: error: <uninhabited> has no attribute "save"
  course/flow.py:1264: error: <uninhabited> has no attribute "get_most_recent_grade"
  

[refi64]

Also, I can confirm that 9496d6f was the root cause; temporarily reverting it made the errors go away.

[gvanrossum]

Thanks for the great investigation! Hopefully Jukka knows how to fix it.

[refi64]

Reduced test case:

# Run mypy with --strict-optional
from typing import Any, Optional

class A(Any): pass

def f(a: Optional[A]):
    if a is not None:
        reveal_type(a)

(The Any stemmed from a class inside of a non-existent import, since --ignore-missing-imports was passed).

Ironically enough, the bad commit's message says:

In particular, this helps with classes that have Any base classes.

:/

[refi64]

Also, this was caused by the same commit:

from typing import Any, Union

class A(Any): pass
class B: pass

def f(a: Union[A, B]):
    if not isinstance(a, B):
        reveal_type(a)  # Union[<ERROR>, <ERROR>]

[JukkaL]

Oh well, I knew that the bad commit was only a partial fix, but I didn't foresee these problems. A more complete fix that I was working on caused many problems with internal Dropbox code. The bad commit fixed other urgent issues so just reverting it is not a good option. I'll look at finishing up the more complete fix.