Add GitHub workflow to ensure formatting is not broken on a set of pilot projects

[ahoppen]

To understand whether a PR breaks the formatting behavior of real-world code, add a GitHub action that formats a small set of real world projects and ensures that swift-format lint does not produce any errors.

Run that shows how this workflow looks like if it discovers a failure: https://github.com/ahoppen/swift-format/actions/runs/19324836211/job/55273496880?pr=13

Since this job currently doesn’t pick up related PRs when checking out the projects to format, I would not mark it as a required check right now. Rather, I’d like to just run this to provide some signal to the author of a PR and to be able to decide if the formatting change is acceptable or not.

[allevato]

Very nice!

Is there a way we could get the diff of the code before and after running the just-built swift-format? That would be even more helpful to see in the logs than just the lint warnings about spaces and such.

[bnbarham]

Is there a way we could get the diff of the code before and after running the just-built swift-format?

Could do a format + git diff instead? I can update after if you'd prefer to just get this in @ahoppen

[ahoppen]

I was thinking the same but we also need to run swift-format lint because there are some issues that will be discovered during linting, like having lowercase types.

Since we need to run the linting step anyway, I’d suggest getting this in as-is and doing the git diff approach in a follow-up PR.

[allevato]

Since we need to run the linting step anyway, I’d suggest getting this in as-is and doing the git diff approach in a follow-up PR.

Works for me!