rubocop: The pyyaml resource requires depends_on "libyaml"

[issyl0]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

• The "pyyaml" resource requires depends_on "libyaml", so make the FormulaAudit/ResourceRequiresDependencies handle both uses_from_macos and depends_on.
• Fail nicely when a formula has no resources.

[timsutton]

Maybe this is a good place to discuss whether libyaml should be also added if ruamel.yaml is a dependency? (As an alternative to PyYAML)

It seems like it might drop back to a pure-python version but use libyaml if it's available?

[p-linnane]

Now that we have this Rubocop we can easily extend it as we identify more situations like this. I'm thinking of the formulae that can't use our python-cryptography formula or the bcrypt resource which both need Rust to build. These are just the most pressing ones for our Python vendoring project.

[MikeMcQuaid]

Thanks @issyl0!