FEATURE: `-l`/`--files-with-updates` option for `swift format`.

[jglogan]

As a swift-format user, I can run my formatting rules with a dry-run option that only outputs the pathnames of files that would be formatted, so that I can easily implement user friendly check scripts or git hooks that can operate on my projects non-destructively.

See also gofmt -l: https://pkg.go.dev/cmd/gofmt

I thought I might take a crack at this feature but wanted to throw it up as an issue in case this feature exists in some form now and I just missed it, or in case it's considered not a good fit for the tool.

Searched through all the issues and couldn't find duplicates.

[allevato]

Running swift-format in lint mode gets you basically this, does it not? It would report any findings where it would have made changes in format mode. If all you care about is the filenames, it's easy enough to scrape that from the output with shell tools.

I suppose one distinction is that this would also flag violations from lint-only rules (rules that can't be auto-corrected in format mode), and maybe you don't want those for some reason? If that's the case, you could use a configuration that disables all of the lint-only rules, leaving behind only the formatting rules and the pretty printer.

Is there something else missing?

[jglogan]

Right now we aren't running the linter in our CI workflow, so I was just looking at what swift-format format did.

I can see if we can make that work.