Add ros2 pkg depends verb

[Miko997]

Description

Add ros2 pkg depends <package_name> to print the package's direct declared dependencies.

The verb reads the installed package.xml, evaluates dependency conditions against the current environment, and prints unique dependency names in sorted order. Recursive lookup and dependency-type filters are outside this PR.

Addresses #44

Is this user-facing behavior change?

Yes. ros2 pkg now provides a depends verb for installed packages.

Additional Information

Validation:

• focused unit and CLI tests: 2 passed
• ros2pkg tests excluding unavailable xmllint: 6 passed, 1 deselected
• copyright, flake8, and pep257: 3 passed
• git diff --check

xmllint was not available in the test environment. This PR does not change XML files.

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[fujitatomoya]

what is the difference between this and ros2 pkg xml | grep? for maintainability, we do not want to maintain the overlapped features for sure.

besides, #44 is originally created almost 10 years ago. i am not sure if there are any requests from community... at least, it's been 10 years...

[Timple]

Would the outcome be different than

colcon list --names-only --packages-up-to <package_name>

?

[fujitatomoya]

@Miko997 a couple of questions here before starting review, please have them checked out.

[Miko997]

The outcome is different. ros2 pkg xml | grep returns raw XML lines, so it can include duplicates and dependencies whose conditions are false. colcon list --packages-up-to returns the recursive build set from a source workspace, including the target package.

This verb reads an installed package from the ament index and prints its unique direct dependencies after evaluating conditions. It does not require a source workspace or colcon.

I have not found newer demand beyond #44. If that installed-package use case does not justify another verb, I am happy to close the PR.

[Timple]

Thanks for the clarification!