Recipe - Apply actionlint & shellcheck suggestions

[aalmiray]

actionlint is a static checker for GH Actions. Many of the problems identified by it could be solved by OpenRewrite rules. actionlint can also report problems identifiable by shellcheck.

Shellcheck rules could by provided independently from GH actions.

[sambsnyd]

Good idea. I don't know when we would prioritize creating something like this ourselves, but would be happy to accept it as a contribution.

[timtebeek]

Adding some links that might be helpful for anyone picking this up.

Integrating with ShellCheck shows us there are currently a number of machine readable output formats: JSON, XML, GCC and diff. Perhaps the diff would be easiest to get started; recipes should not assume there's a readily available filesystem, but perhaps one can be emulated in memory from the resources we have.

Separately there's a differential shellcheck page and implementation we can use as inspiration when we run on PRs rather than full projects. That's out of scope, but thought to mention it as a cool find for future work.

Action lint also has various output formats and current integrations. It does not immediately result in a diff to apply though, so harder for automated changes. We could add markers that are then displayed or inserted as comments, but it's not an immediate fix for some of the feedback that I've seen it produce.