[Pankraz76]

Closes #2715

Why

Many builds run spotlessApply locally as part of build, so developers never see what Spotless fixed. The issue asks for a way to tell when spotlessApply actually changed something, and which files. The obvious workaround (doLast { if (didWork) ... }) doesn't work today, because SpotlessApply reports didWork = true even when it wrote nothing:

• when there is nothing to apply, it copies the format task's didWork, so it shows SUCCESS every time spotlessJava re-runs (e.g. on the build right after a fix)
• clean files that are byte-identical to the source were still copied and counted

What

• Accurate didWork: SpotlessApply reports work only when it actually rewrote a source file; otherwise it shows UP-TO-DATE. Clean files identical to the source are no longer copied, so their mtimes aren't touched.
• Changed-files report: every SpotlessApply writes the files its last run rewrote to build/spotless/<taskName>-changed-files.txt. That's one project-relative /-separated path per line, sorted, UTF-8. The report is empty if nothing changed, and it is still written when the task then fails on lints. The location is configurable via the new changedFilesReport property:

tasks.withType(com.diffplug.gradle.spotless.SpotlessApply).configureEach {
  def report = changedFilesReport
  doLast {
    if (didWork) {
      logger.lifecycle("Spotless fixed:\n" + report.get().asFile.text)
    }
  }
}

The report property is @Internal on purpose. A task that declares outputs but no inputs can be considered up-to-date by Gradle, and apply must always run.

Not changed (the "load-bearing" part from the issue discussion)

registerApplyAlreadyRan still runs first, so spotlessCheck still skips its work after apply ran. The lint failure path is unchanged.

Visible behaviour change

On the build right after a fix, the format task still runs (its input was rewritten), but the apply tasks are now UP-TO-DATE instead of SUCCESS. UpToDateTest asserted the old outcome in exactly that step, so those three steps now assert per-task outcomes.

Tests

New SpotlessApplyChangedFilesTest, written first and confirmed failing before the fix:

• unformatted files → report lists exactly the rewritten files
• only clean files → apply UP-TO-DATE, empty report
• second run with nothing to fix → report reset to empty
• lint failure → report still lists the fixed file
• custom report location read from a build script in doLast

Ran locally, all passing (76/76):

• the new test
• UpToDateTest, ConfigurationCacheTest, GitRatchetGradleTest, IdeHookTest, MultiProjectTest, ErrorShouldRethrowTest
• IndependentTaskTest, PaddedCellTaskTest, DiffMessageFormatterTest, CompositeBuildRunToFixMessageTest, SpotlessTaskImplTest
• spotlessCheck and :plugin-gradle:check, including SpotBugs

plugin-gradle/CHANGES.md and the README are updated. Only plugin-gradle is affected, so the lib and Maven changelogs are untouched.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MTr23z6ccMd2shvyTaTFVY