Correct workflow .yml to add format check to block unformatted PRs

[vtjeng]

I'd like to add a check to ensure that JuliaFormatter has been run on PRs submitted to my repo so that contributors (mostly myself) can't merge code that isn't properly formatted.

• Is the version at JuliaFormatter or the version in this repo the preferred version?
• In addition, is the failure on this PR in JuliaFormatter to do with the PR or an issue with the workflow specified in that repo?

[domluna]

1. the latest version is ideal, that example just shows how to pick a different version.
2. it's the PR, that workflow checks the PR is formatted. The workflow file in JuliaFormatter.jl is a little different because it's checking the JuliaFormatter.jl repo itself so it's a bit more involved. That being said that workflow was created a while ago so it may be overkill at this point.

[vtjeng]

Thanks! I ended up implementing a modified version of the .yml that pins a different version so that I could ensure that the commands run on CI and locally (when users are trying to fix their issues) would be the same.

Here's the PR and a sample error message.

[domluna]

@vtjeng the latest version of JuliaFormatter now returns a bool from format or format_file that is true if the files are already formatted correctly, false otherwise. This should makes this check easier.

[vtjeng]

Thanks! I like the check as written

      - name: 'Check that running `format` is a no-op.'
        run: |
          julia -e '
          out = Cmd(`git diff --name-only`) |> read |> String
          if out == ""
              exit(0)
          else
              @error "Some files did not meet the formatting guidelines. Run ./scripts/format.sh to fix."
              write(stdout, "\nFiles not meeting formatting guidelines:\n")
              write(stdout, out)
              write(stdout, "\nRun ./scripts/format.sh to fix.")
              exit(1)
          end'

because it helps users identify which files aren't formatted properly, but I'll make sure to use that in other scripts I'm writing.