test typing

[davidism]

Add a typing_examples.py file that has examples of different uses of Flask with type annotations. For example, show examples of views that return each valid return type for a view. We can run mypy against this to check that using Flask passes typing, not just the internal type checking.

[davidism]

See structlog for an example: https://github.com/hynek/structlog/blob/main/typing_examples.py

[lecovi]

Ok, I think I can handle this. Let me get this straight first:
You want a typing_examples.py, let's say inside the examples directory, that shows a Flask App with differents View types for help users to understand how to type their applications. Am I correct?

[davidism]

Yes, and probably other things like registering error handlers, before_request functions, etc. The application itself doesn't have to make much sense, it just has to be something we can run mypy against.

cc @hynek

[hynek]

Yeah to be clear: that code doesn't have to be executable at all. Use nonsense values! They just have to have correct types.

[lecovi]

Awesome! I will give it a shot If you let me 😉

[davidism]

We've now merged in some initial tests for @app.route and @app.errorhandler. I'll close this now, although I welcome anyone to add more typing tests for other parts of the code.