Sparse checkouts broken by spotless lint

[LetianLi]

Describe why this should be added

PR #13170 added spotless to linting, which I believe broke builds in sparse checkouts. Specifically, the ratcheting seems to be causing the issue. This means contributors need to clone the entire repo which slows development.

If spotless ratcheting is to be used only in CI, it might be better to gate the ratchetFrom inside keiyoshi.lint.gradle.kts with

if (System.getenv("CI") == "true") {
    ratchetFrom = "68ed874a42038f4efd001c555cba9bf7de8474d7"
}

Other details

I'm getting the following error for the tasks spotlessGradle, spotlessKotlin, spotlessXml whenever I try to build an extension.

> org.eclipse.jgit.errors.CorruptObjectException: Invalid path: .github/

Acknowledgements

• I have searched existing issues both open & closed, and confirm that this is a new unreported issue.
• I have written a short but informative title.
• If this is an issue with the app itself, I should be opening an issue in the app repository.
• I have updated the app to version 0.19.3.
• I have updated the extension to the latest version (as listed on the extensions listing page).
• I will correctly fill out all of the requested information in this form.

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[Starmania]

Use git sparse-checkout init --no-sparse-index to stop Git from grouping excluded folders into single "directory" entries. This fixes the build crash because JGit (used by Spotless) hasn't caught up with modern Git 2.31+ features; it sees a folder entry like .github/ in the index and freaks out, thinking it’s a corrupted file with a "zero-length name."

While this adds a bit of bulk back to your .git/index file, it’s the only way to keep the build passing until JGit finally updates its core logic to handle sparse index markers properly. Good news is that it keeps build time low.

[LetianLi]

Doesn't quite explain why removing ratcheting fixed it.

Will be fixed by #13197, hopefully.

[Starmania]

The exact explanation is that spotless, the formater, is dependence of JGit. More exactly, when using rachetMode, it ask JGit which modifications happens since this tag or this commit. But JGit does not support well every features of the latest version of git, and does not support sparse-checkout.

And so, if a folder contain files that were modified but does not exist because of sparse-checkout in the git index, it fail because it does not understand what type of file it is.

Spotless does not invoke JGit on sparse-checked files and folders if the rachet mode is not active, this is why this PR would fix the problem.

[LetianLi]

This makes sense, so it's a dependency error that occurs only in ratcheting.