Make Actionlint Directly Invokable as an Action Itself

[norwd]

Currently, there are two ways of running actionlint in a GitHub Action workflow:

1. Running the download script to install actionlint and execute it from a run: step:

   - name: Check workflow files
     shell: bash
     run: |
       bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
       ./actionlint -color

2. Running actionlint from a docker container

   - name: Check workflow files
     uses: docker://rhysd/actionlint:latest
     with:
       args: -color

Both of these two options have some drawbacks. Option 1 requires either always running the download script from the main branch (which may be unstable), or specifying a stable tag (which needs to be manually updated when new versions are released as Dependabot won't suggest updates). Option 2 has the benefit of being tied to a stable version, e.g. docker://rhysd/actionlint:v<TAG>, however, it can only be configured by passing in the args: property as a monolithic string, instead of separate inputs with clear defaults and descriptions.

This pull request solves this by adding an action.yml file to the root that defines inputs: and executes actionlint internally. Essentially wrapping a run actionlint from a workflow. The key benefits here are clearly defined inputs and enabling Dependabot updates.

This resolves #262

[rhysd]

Adding an action to this repository is confusing because tags of this repository are for actionlint command line tool. For example, adding a new feature to the action causes a minor version bump even if the actionlint command has no new features.

Currently actionlint can be used with only two steps; download it and just run it.

https://github.com/rhysd/actionlint/blob/main/docs/usage.md#use-actionlint-on-github-actions

I don't feel the benefit of just converting the two steps into one is a compelling argument against the problem I explained above.

[norwd]

Adding an action to this repository is confusing because tags of this repository are for actionlint command line tool. For example, adding a new feature to the action causes a minor version bump even if the actionlint command has no new features.

Currently actionlint can be used with only two steps; download it and just run it.

https://github.com/rhysd/actionlint/blob/main/docs/usage.md#use-actionlint-on-github-actions

I don't feel the benefit of just converting the two steps into one is a compelling argument against the problem I explained above.

That's fair 🙂, I just thought since I had a fork lying around I might as well offer to merge it. Feel free to close this and the linked issue.

[rhysd]

Keeping the fork or creating a separate repository for it sounds much better than merging this. Thank you for making the action 👍. Then closing.