[Flask-Cors] Update type annotation for origins to also allow Pattern

[wvanbergen]

Small fix: this updates the type annotation for the origins argument for CORS() and CORS.init_app to also accept Patterns. Also, use Iterable rather than list to not cause compatibility issues.

• This reflects the typing of the origins argument of the cross_origin decorator.
• This matches the documentation: https://corydolphin.github.io/flask-cors/extension/
• This reflects what we have been running in production for many years.

[github-actions]

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

[brianschubert]

Thanks! See remarks below. This change looks good, but I'm noticing some inconsistencies with the previous annotations that we should fix while we're here.

[brianschubert]

Unless I'm missing something, it appears that these function assume that the options have already been processed with serialize_options, which wraps a single string or pattern object in a list to ensure that origins is iterable. They'll raise a TypeError if you attempt to use a plain pattern object.

It also doesn't appear that None (or [None]) is a valid value (will also raise a TypeError). I'm guessing that that was added since the options are accessed with options.get(...), which suggests that None could be returned. But in actuality the options dict is pre-populated with the values from DEFAULT_OPTIONS, which sets non-None defaults, so I don't think a None value is ever valid?

A few examples of what I'm talking about:

# Non-iterable origins wrapped in list
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; print(c.serialize_options({"origins": "foo"}))'
{'origins': ['foo'], 'allow_headers': [None]}

# Raise on plain pattern object for origins
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; import re; print(c.get_cors_origins({"origins": re.compile("foo")}, "foo"))'
TypeError: argument of type 're.Pattern' is not a container or iterable

# Raise on None for origins
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; import re; print(c.get_cors_origins({"origins": None}, "foo"))'
TypeError: argument of type 'NoneType' is not a container or iterable

# Raise on [None] for origins
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; import re; print(c.get_cors_origins({"origins": [None]}, "foo"))'
TypeError: argument of type 'NoneType' is not a container or iterable

Does that match your experience?

The same appears to be true for allow_headers, so I'd suggest using the same type for it. It also appears that some of the other options can't be None in practice -- up to you if you want to try to fix those while we're here.

Suggested change

	origins: str | Pattern[str] | Iterable[str | Pattern[str]] | None
	methods: str | list[str] | None
	expose_headers: str | list[str] | None
	allow_headers: str | list[str] | None
	origins: Iterable[str | Pattern[str]]
	methods: str | list[str] | None
	expose_headers: str | list[str] | None
	allow_headers: Iterable[str | Pattern[str]]

[brianschubert]

Per above, it doesn't appear that passing None is valid.

Suggested change

	origins: str | Pattern[str] | Iterable[str | Pattern[str]] | None = ...,
	origins: str | Pattern[str] | Iterable[str | Pattern[str]] = ...,