Typecheck xmllint with ament_mypy

[InvincibleRMC]

Add ament_mypy type checking to ament_xmllint.

[InvincibleRMC]

Hmm it seems colcon cannot resolve a build tree since ament_mypy and ament_xmllint are test_depends of each other. Looking at colcon there seems to be an open issue covering a very similar situation except here it is a little more narrow in scope focused only on test_depend and that issue includes exec_depend. Looking at the other linters it seems we just lint in a tree where flake8 only lints itself to avoid this circular build limitation. I guess type checking the other linters with ament_mypy will have to wait.

[cottsay]

I don't think we should be importing from a private module.

Suggested change

	from _pytest.config import Config
	from pytest import Config

[cottsay]

Following the pattern in other files, only a single newline between copyright and imports.

Suggested change

[cottsay]

This will effectively become a new dependency for all of ROS 2. Is there any way to avoid it?

[InvincibleRMC]

@cottsay Thanks for the feedback unfortunately due to this linters can't lint other linters.

[cottsay]

Thanks for the feedback unfortunately ... linters can't lint other linters.

I see. While I think there's an acute risk of this issue manifesting with linters-on-linters, I don't think this statement is universally true. That said, this change would create a cyclic dependency under the current interpretation of dependency scopes.

How would you like to move forward with this PR?

[InvincibleRMC]

I think leaving in draft is probably best since this would be a good feature if the definition of cyclic dependencies ever gets updated. If you would prefer closing and possible future re-opening is better I would be fine with that.