Add mypy to CI

[haacked]

A recent issue #187 noted that a recent PR (#182) introduced new errors when running mypy .. Shout out to @rafaeelaudibert for jumping on a fix (#188).

In the issue, @rafaeelaudibert asked (emphasis mine):

Agh, great catch, let me fix this. I don't understand why CI didn't catch this

Well I found the reason. CI doesn't run mypy. 😆

And for good reason, it would produce almost 700 errors. However, we can try to be good citizens moving forward by not allowing new mypy errors and fix existing ones over time.

So this PR does the following:

1. Adds additional dev dependencies related to running mypy.
2. Adds a baseline filter file created with mypy-baseline
3. Adds mypy . | mypy-baseline filter to the CI. This should only warn on new errors.
4. Adds a mypy.ini so we can configure the mypy errors we care about.

When someone fixes old mypy errors, they'll need to run mypy . | mypy-baseline sync to generate a new baseline.

Open Question for Reviewers

• Do we care about all of the mypy warnings? Right now I have them all set to True.
• I ignored all errors in tests. Seems good for now, but maybe we want some checking in the future?

[greptile-apps]

PR Summary

This PR adds mypy type checking to the CI pipeline to prevent future type-related issues, addressing a gap where type errors weren't being caught during continuous integration.

• Added mypy.ini with strict type checking configuration, ignoring test files and third-party imports
• Created mypy-baseline.txt to track ~700 existing type errors while preventing new ones
• Added mypy and related type stub packages to dev dependencies in setup.py
• Integrated mypy . | mypy-baseline filter command in CI workflow to catch only new type errors

_{4 file(s) reviewed, 7 comment(s)
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[rafaeelaudibert]

Thank you!

I don't have any suggestions on what the setup should look like. We should try to make it look the closest possible to our posthog/posthog project, but I'm fine to just use a separate subset of checks

[haacked]

I don't have any suggestions on what the setup should look like. We should try to make it look the closest possible to our posthog/posthog project, but I'm fine to just use a separate subset of checks

Good idea! I updated the mypy.ini here to look like https://github.com/PostHog/posthog/blob/master/mypy.ini.