Mypy 0.710 broke support for inline weak import comments

[AdiRishi]

Are you reporting a bug, or opening a feature request?
I'm reporting a breaking change in mypy 0.710

Please insert below the code you are checking with mypy
The following import at the top of a file no longer works

# mypy: weak=import

What is the actual behavior/output?
<path_to_file>:1: error: Unrecognized option: weak = import

What is the behavior/output you expect?
It is expected that mypy allows weak imports in the file, or at the very least doesn't raise an error.

What are the versions of mypy and Python you are using?
Python version: 3.7
mypy version: 0.710
mypy-extensions version: 0.4.1
typed-ast version: 1.4.0

What are the mypy flags you are using? (For example --strict-optional)
The exact command we are running is
mypy --ignore-missing-imports --disallow-untyped-defs --strict-optional

I have yet to find which exact version of mypy had this breaking change.
I just thought I'd make this issue, and see if you are aware/have a recommended fix for this.

I appreciate any help you provide and I'm happy to provide further details if necessary.

[msullivan]

What does # mypy: weak=import mean in this context? It doesn't mean anything to mypy and I don't think it ever has. Is there some other tool that cares about it?

Starting with version 0.710, # mypy: comments at the toplevel are understood by mypy to be configuration options.

If there is a particularly well established use of # mypy: comments already, then we might need to rethink this, but otherwise we're probably not fixing this.

[JelleZijlstra]

Apparently this used to do something before mypy 0.4.5: http://mypy-lang.blogspot.com/2016/10/mypy-045-released.html (see under "Deprecations and Removals"). Mypy has been ignoring these comments for years though.

[AdiRishi]

As far as I can tell, # mypy: weak=import has been a comment that did things in the past.
You can see other people recommending it in past comments - #971 (comment)

Your explanation on why this is now an error makes sense, weak=import is indeed not a configuration option in mypy.

Unfortunately I couldn't tell you what weak=import does, it's part of some old code we have.
I'm happy if you don't support it going forward, just through I'd bring this up in an issue since this will cause existing builds to fail which use the option

[AdiRishi]

Happy to close this issue with the resolution that this is a won't fix

[msullivan]

Today I learn!