Support tsc to check actions/github-script steps

[nomeata]

This suggest is a sibling of #55. I see more an more actions migrating from simple bash to actions/github-script, but thus losing any actionlint guardrails. It would be great if actionlint could somehow check actions/github-script scripts.

In #55 eslint was suggested, but there are good reasons why supporting that is not easy.

I wonder if using the typescript compiler to check the JavaScript snippts (given that JavaScript is a subset of typescript) would work? Maybe it is already preinstalled?

One hurdle is of course that the snipptes passed to actions/github-script probably has to be wrapped in a type-annotated function declaration that matches what actions/github-script is doing; I don’t know how hard and how reliable that is.

[rhysd]

It would be nice to have. Thanks for your suggestion.

Though it is hard to check the script when ${{ }} is used in it, I think we can skip checking such script.

Things unclear for me:

• Some non-standard global objects are defined. They need separate type definitions which typically sit in types directories of npm packages. How can we pass the type definitions to tsc on checking scripts?
  • github A pre-authenticated octokit/rest.js client with pagination plugins
  • context An object containing the context of the workflow run
  • core A reference to the @actions/core package
  • glob A reference to the @actions/glob package
  • io A reference to the @actions/io package
  • exec A reference to the @actions/exec package
• How is TypeScript's --checkJs useful? I don't have experience to use the option.
• Scripts can be a single return statement like script: return "hello". How can we handle this?