Propagate aspect to generating rules by default

[ulfjack]

This should make the aspect more reliably collect licenses from included files.

• Tests pass
• Tests and examples for any new features.
• Appropriate changes to README are included in PR

[ulfjack]

Maybe setup GitHub Actions?

[aiuto]

I'll take this PR for now, but without great test cases (we have some, just not ready for public) it's not clear if it will stick.

[ulfjack]

Hi @aiuto!

We aren't using this code at all. I wrote an aspect for our own use that works with our current license definitions and I've been diffing the result against our previous license collection implementation to check if we're missing anything. That said, I was hoping that we could eventually migrate to a common implementation but it doesn't currently look like it.

This implementation has several shortcomings that make it unusable for us:

• it didn't collect through output file dependencies (fixed in this PR)
• we have a custom license type that also has attached file references to license and notice files as well as URLs pointing at the original source (this information is required for some cloud marketplace deployments)
• the list of attributes it traverses is too narrow; it's actually hard to come up with a complete list, but here's what we're using for a Java application: "deps", "exports", "jars", "resources", "runtime_deps", "srcs"; for other languages, we may need to collect from even more attributes (e.g., hdrs for C++)
• it doesn't enforce our repo-specific annotation rules: we're enforcing license annotations for all rules under our third_party directory and a subset of external workspaces; some of that is specific to our use case

I primarily sent you a patch for this to help prevent other people going down the rabbit hole of figuring out how to collect licenses through output file dependencies.

Thanks!

-- Ulf