sonarqube-gradle-pluginで `Component key * not found` となった時

org.sonarsource.scanner.gradle:sonarqube-gradle-plugin を使っていて、設定次第ではまれにこのようなエラーが出る場合がある:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':sonarqube'.
> Unable to load component class org.sonar.scanner.report.MetadataPublisher

* Try:
Run with --debug option to get more log output. Run with --scan to get full insights.

* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':sonarqube'.
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:103)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:73)
    at org.gradle.api.internal.tasks.execution.OutputDirectoryCreatingTaskExecuter.execute(OutputDirectoryCreatingTaskExecuter.java:51)
    at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:59)
    at org.gradle.api.internal.tasks.execution.ResolveTaskOutputCachingStateExecuter.execute(ResolveTaskOutputCachingStateExecuter.java:54)
    at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:59)
    at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:101)
    at org.gradle.api.internal.tasks.execution.FinalizeInputFilePropertiesTaskExecuter.execute(FinalizeInputFilePropertiesTaskExecuter.java:44)
    at org.gradle.api.internal.tasks.execution.CleanupStaleOutputsExecuter.execute(CleanupStaleOutputsExecuter.java:91)
    at org.gradle.api.internal.tasks.execution.ResolveTaskArtifactStateTaskExecuter.execute(ResolveTaskArtifactStateTaskExecuter.java:62)
    at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:59)
    at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:54)
    at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:43)
    at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:34)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker$1.run(DefaultTaskGraphExecuter.java:256)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:249)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:238)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.processTask(DefaultTaskPlanExecutor.java:123)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.access$200(DefaultTaskPlanExecutor.java:79)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:104)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:98)
    at org.gradle.execution.taskgraph.DefaultTaskExecutionPlan.execute(DefaultTaskExecutionPlan.java:663)
    at org.gradle.execution.taskgraph.DefaultTaskExecutionPlan.executeWithTask(DefaultTaskExecutionPlan.java:597)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.run(DefaultTaskPlanExecutor.java:98)
    at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
    at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
    at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
Caused by: java.lang.IllegalStateException: Unable to load component class org.sonar.scanner.report.MetadataPublisher
    at org.sonar.core.platform.ComponentContainer$ExtendedDefaultPicoContainer.getComponent(ComponentContainer.java:65)
    at org.picocontainer.DefaultPicoContainer.getComponent(DefaultPicoContainer.java:621)
    at org.picocontainer.parameters.CollectionComponentParameter.getArrayInstance(CollectionComponentParameter.java:334)
    at org.picocontainer.parameters.CollectionComponentParameter.access$100(CollectionComponentParameter.java:49)
    at org.picocontainer.parameters.CollectionComponentParameter$1.resolveInstance(CollectionComponentParameter.java:139)
    at org.picocontainer.parameters.ComponentParameter$1.resolveInstance(ComponentParameter.java:141)
    at org.picocontainer.injectors.SingleMemberInjector.getParameter(SingleMemberInjector.java:78)
    at org.picocontainer.injectors.ConstructorInjector$CtorAndAdapters.getParameterArguments(ConstructorInjector.java:309)
    at org.picocontainer.injectors.ConstructorInjector$1.run(ConstructorInjector.java:335)
    at org.picocontainer.injectors.AbstractInjector$ThreadLocalCyclicDependencyGuard.observe(AbstractInjector.java:270)
    at org.picocontainer.injectors.ConstructorInjector.getComponentInstance(ConstructorInjector.java:364)
    at org.picocontainer.injectors.AbstractInjectionFactory$LifecycleAdapter.getComponentInstance(AbstractInjectionFactory.java:56)
    at org.picocontainer.behaviors.AbstractBehavior.getComponentInstance(AbstractBehavior.java:64)
    at org.picocontainer.behaviors.Stored.getComponentInstance(Stored.java:91)
    at org.picocontainer.DefaultPicoContainer.instantiateComponentAsIsStartable(DefaultPicoContainer.java:1034)
    at org.picocontainer.DefaultPicoContainer.addAdapterIfStartable(DefaultPicoContainer.java:1026)
    at org.picocontainer.DefaultPicoContainer.startAdapters(DefaultPicoContainer.java:1003)
    at org.picocontainer.DefaultPicoContainer.start(DefaultPicoContainer.java:767)
    at org.sonar.core.platform.ComponentContainer.startComponents(ComponentContainer.java:135)
    at org.sonar.core.platform.ComponentContainer.execute(ComponentContainer.java:122)
    at org.sonar.scanner.task.ScanTask.execute(ScanTask.java:48)
    at org.sonar.scanner.task.TaskContainer.doAfterStart(TaskContainer.java:82)
    at org.sonar.core.platform.ComponentContainer.startComponents(ComponentContainer.java:136)
    at org.sonar.core.platform.ComponentContainer.execute(ComponentContainer.java:122)
    at org.sonar.scanner.bootstrap.GlobalContainer.executeTask(GlobalContainer.java:131)
    at org.sonar.batch.bootstrapper.Batch.doExecuteTask(Batch.java:116)
    at org.sonar.batch.bootstrapper.Batch.executeTask(Batch.java:111)
    at org.sonarsource.scanner.api.internal.batch.BatchIsolatedLauncher.execute(BatchIsolatedLauncher.java:63)
    at org.sonarsource.scanner.api.internal.IsolatedLauncherProxy.invoke(IsolatedLauncherProxy.java:60)
    at com.sun.proxy.$Proxy96.execute(Unknown Source)
    at org.sonarsource.scanner.api.EmbeddedScanner.doExecute(EmbeddedScanner.java:233)
    at org.sonarsource.scanner.api.EmbeddedScanner.runAnalysis(EmbeddedScanner.java:151)
    at org.sonarqube.gradle.SonarQubeTask.run(SonarQubeTask.java:99)
    at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73)
    at org.gradle.api.internal.project.taskfactory.StandardTaskAction.doExecute(StandardTaskAction.java:46)
    at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:39)
    at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:26)
    at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:788)
    at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:755)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$1.run(ExecuteActionsTaskExecuter.java:124)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:113)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:95)
    ... 30 more
Caused by: java.lang.IllegalStateException: Unable to load component class org.sonar.scanner.rule.ModuleQProfiles
    at org.sonar.core.platform.ComponentContainer$ExtendedDefaultPicoContainer.getComponent(ComponentContainer.java:65)
    at org.picocontainer.DefaultPicoContainer.getComponent(DefaultPicoContainer.java:632)
    at org.picocontainer.parameters.BasicComponentParameter$1.resolveInstance(BasicComponentParameter.java:118)
    at org.picocontainer.parameters.ComponentParameter$1.resolveInstance(ComponentParameter.java:136)
    at org.picocontainer.injectors.SingleMemberInjector.getParameter(SingleMemberInjector.java:78)
    at org.picocontainer.injectors.ConstructorInjector$CtorAndAdapters.getParameterArguments(ConstructorInjector.java:309)
    at org.picocontainer.injectors.ConstructorInjector$1.run(ConstructorInjector.java:335)
    at org.picocontainer.injectors.AbstractInjector$ThreadLocalCyclicDependencyGuard.observe(AbstractInjector.java:270)
    at org.picocontainer.injectors.ConstructorInjector.getComponentInstance(ConstructorInjector.java:364)
    at org.picocontainer.injectors.AbstractInjectionFactory$LifecycleAdapter.getComponentInstance(AbstractInjectionFactory.java:56)
    at org.picocontainer.behaviors.AbstractBehavior.getComponentInstance(AbstractBehavior.java:64)
    at org.picocontainer.behaviors.Stored.getComponentInstance(Stored.java:91)
    at org.picocontainer.DefaultPicoContainer.getInstance(DefaultPicoContainer.java:699)
    at org.picocontainer.DefaultPicoContainer.getComponent(DefaultPicoContainer.java:647)
    at org.sonar.core.platform.ComponentContainer$ExtendedDefaultPicoContainer.getComponent(ComponentContainer.java:63)
    ... 75 more
Caused by: Failed to load the quality profiles of project 'project': Component key 'project' not found

最後のここに注目:

Caused by: Failed to load the quality profiles of project 'project': Component key 'project' not found

この Component key '*' not found の部分がプロジェクトのルートディレクトリ名だった場合、恐らく問題は簡単。

ドキュメントによると、このプラグインはprojectKey設定の際、デフォルトではルートのプロジェクト名を用いる。
そしてGradleはルートのプロジェクトにプロジェクト名が設定されていない場合、そのプロジェクトのルートディレクトリ名を用いる。

開発現場ではルートディレクトリ名はGitリポジトリ名とリンクしていることが多いため、開発者ほぼ全員が偶然期待通りの設定がデフォルト値として用いられる。
しかし例えばCircleCIなどのSaaSでは、プロジェクトがcloneされる先が ~/project となるため、この前提が崩れるのである。

解決方法

このように環境によって不安定な状態で用いるのは望ましくないが、手っ取り早く治すなら プロジェクトルートにある settings.gradle へ以下の1行を書き足せば良い。

rootProject.name = '期待するディレクトリ名'

余談

私はこれで2営業日とかしました