Use swift-format for Swift file formatting

[jasikpark]

Try 3 of #254, #256

This adds a script called swift-format.sh that ignores the files listed in .swiftformatignore while that feature is being added into swiftlang/swift-format.

swift-format is shipped with XCode 16 and is included in the Github macos runners. There's a menuitem in XCode that allows formatting the file you're viewing. A good blog post is at: https://calebhearth.com/swift-format-github-action

Under Editor -> Structure -> Format with swift-format:

This script has been vendored from swiftlang/github-workflows and adds a comment mentioning where it was vendored from and which edits have been made to it differing from the original source.

A quirk is that this script relies on the ignore file being at the top level, so it's a bit brittle. We could honestly just hardcode the ignore value in the script, but 🤷

#263 will enable the format check and format all swift code, then a PR after that will git blame ignore the formatting PR.

Testing

To test, you can run ./swift-format.sh from the root of the repo and see that swift code is formatted. To test the "check" run ./swift-format.sh check and see that there is a git diff outputted and that the exit code was unsuccessful.

You may also see a failed run at https://github.com/DefinedNet/mobile_nebula/actions/runs/13444683597/job/37567211304?pr=261 while it still exists.

Refs:

• Ability To Turn Off Formatting For Subdirectory swiftlang/swift-format#870
• https://github.com/swiftlang/github-workflows/blob/main/.github/workflows/scripts/check-swift-format.sh
• Ability To Turn Off Formatting For Subdirectory swiftlang/swift-format#873 is the stalled PR that would add directory ignores.