Gradle issue: Using the incremental task API without declaring any outputs has been deprecated.

[ZacSweers]

Gradle 5.5.1
Spotless 3.24.0
MacOS 10.14.6
Github repo: https://github.com/zacsweers/catchup

Full trace reported from gradle below. Unfortunately it doesn't say where the issue is from in code, just that it occurs when running the spotlessKotlin task on any project that applies it

Warning deprecated usage found: Using the incremental task API without declaring any outputs has been deprecated.

org.gradle.api.internal.changedetection.changes.DefaultTaskExecutionModeResolver.getExecutionMode(DefaultTaskExecutionModeResolver.java:46)
org.gradle.api.internal.tasks.execution.ResolveTaskExecutionModeExecuter.execute(ResolveTaskExecutionModeExecuter.java:67)
org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:57)
org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:56)
org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:36)
org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.executeTask(EventFiringTaskExecuter.java:77)
org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:55)
org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:52)
org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:416)
org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:406)
org.gradle.internal.operations.DefaultBuildOperationExecutor$1.execute(DefaultBuildOperationExecutor.java:165)
org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:250)
org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:158)
org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:102)
org.gradle.internal.operations.DelegatingBuildOperationExecutor.call(DelegatingBuildOperationExecutor.java:36)
org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:52)
org.gradle.execution.plan.LocalTaskNodeExecutor.execute(LocalTaskNodeExecutor.java:43)
org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:355)
org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:343)
org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:336)
org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:322)
org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker$1.execute(DefaultPlanExecutor.java:134)
org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker$1.execute(DefaultPlanExecutor.java:129)
org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.execute(DefaultPlanExecutor.java:202)
org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.executeNextNode(DefaultPlanExecutor.java:193)
org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.run(DefaultPlanExecutor.java:129)
org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
java.base/java.lang.Thread.run(Thread.java:834)

[nedtwigg]

Thanks for finding this! Each SpotlessTask already has one synthetic output file, e.g. for java it is build/spotlessJava, which we write to on every run.

spotless/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessTask.java

Lines 119 to 129 in b6b7f96

	/** Internal use only. */
	@InputFiles
	@Deprecated
	public Iterable<File> getInternalTarget() {
	// used to combine the special cache file and the real target
	return Iterables.concat(ImmutableList.of(getCacheFile()), target);
	}
	private File getCacheFile() {
	return new File(getProject().getBuildDir(), getName());
	}

We could easily list this file as an output, but the trick is we also need to list it as an input (it fixes a tricky up-to-date corner-case, described here). If having this file as both an input and an output triggers their warnings (which would be reasonable), then we can just make another synthetic output and list that as our output.

Until these deprecated warnings become errors, this won't be high on my todo list. Happy to merge a PR before then, or I'll get to it when it becomes urgent.

[ZacSweers]

I'll see what I can do as a PR 👍. They're not errors, but they do warn on every build in gradle 5.x+

[nedtwigg]

Released in 3.24.2