title: Android R8 ArrayIndexOutOfBoundsException
body: <p>I have recently attempted to move over from using ProGuard to using R8 in a project. However in doing so I am receiving the following error when trying to build. Using ProGuard the project builds and runs successfully.</p>
  
  <pre><code>org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':app-project:transformClassesAndResourcesWithR8ForRelease'.
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:110)
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:77)
          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.api.internal.tasks.execution.EventFiringTaskExecuter$1.run(EventFiringTaskExecuter.java:51)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:300)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:292)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:174)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:90)
          at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31)
          at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:46)
          at org.gradle.execution.taskgraph.LocalTaskInfoExecutor.execute(LocalTaskInfoExecutor.java:42)
          at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareWorkItemExecutor.execute(DefaultTaskExecutionGraph.java:277)
          at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareWorkItemExecutor.execute(DefaultTaskExecutionGraph.java:262)
          at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:135)
          at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:130)
          at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker.execute(DefaultTaskPlanExecutor.java:200)
          at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker.executeWithWork(DefaultTaskPlanExecutor.java:191)
          at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker.run(DefaultTaskPlanExecutor.java:130)
          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.ArrayIndexOutOfBoundsException
          at com.android.tools.r8.utils.ThreadUtils.awaitFutures(ThreadUtils.java:21)
          at com.android.tools.r8.shaking.RootSetBuilder.run(RootSetBuilder.java:326)
          at com.android.tools.r8.R8.run(R8.java:287)
          at com.android.tools.r8.R8.run(R8.java:229)
          at com.android.tools.r8.R8.lambda$runForTesting$1(R8.java:220)
          at com.android.tools.r8.utils.ExceptionUtils.withCompilationHandler(ExceptionUtils.java:60)
          at com.android.tools.r8.utils.ExceptionUtils.withR8CompilationHandler(ExceptionUtils.java:48)
          at com.android.tools.r8.R8.runForTesting(R8.java:216)
          at com.android.tools.r8.R8.run(R8.java:129)
          at com.android.builder.dexing.R8Tool.runR8(r8Tool.kt:184)
          at com.android.build.gradle.internal.transforms.R8Transform.transform(R8Transform.kt:244)
          at com.android.build.gradle.internal.pipeline.TransformTask$2.call(TransformTask.java:239)
          at com.android.build.gradle.internal.pipeline.TransformTask$2.call(TransformTask.java:235)
          at com.android.builder.profile.ThreadRecorder.record(ThreadRecorder.java:102)
          at com.android.build.gradle.internal.pipeline.TransformTask.transform(TransformTask.java:230)
          at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73)
          at org.gradle.api.internal.project.taskfactory.IncrementalTaskAction.doExecute(IncrementalTaskAction.java:50)
          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.tasks.execution.ExecuteActionsTaskExecuter$1.run(ExecuteActionsTaskExecuter.java:131)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:300)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:292)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:174)
          at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:90)
          at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31)
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:120)
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:99)
          ... 31 more
          Suppressed: java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException
                  at java.util.concurrent.ForkJoinTask.get(ForkJoinTask.java:1006)
                  at com.android.tools.r8.utils.ThreadUtils.awaitFutures(ThreadUtils.java:21)
                  at com.android.tools.r8.shaking.RootSetBuilder.run(RootSetBuilder.java:326)
                  at com.android.tools.r8.R8.run(R8.java:287)
                  at com.android.tools.r8.R8.run(R8.java:229)
                  at com.android.tools.r8.R8.lambda$runForTesting$1(R8.java:220)
                  at com.android.tools.r8.utils.ExceptionUtils.withCompilationHandler(ExceptionUtils.java:60)
                  at com.android.tools.r8.utils.ExceptionUtils.withR8CompilationHandler(ExceptionUtils.java:48)
                  at com.android.tools.r8.R8.runForTesting(R8.java:216)
                  at com.android.tools.r8.R8.run(R8.java:129)
                  at com.android.builder.dexing.R8Tool.runR8(r8Tool.kt:184)
                  at com.android.build.gradle.internal.transforms.R8Transform.transform(R8Transform.kt:244)
                  at com.android.build.gradle.internal.pipeline.TransformTask$2.call(TransformTask.java:239)
                  at com.android.build.gradle.internal.pipeline.TransformTask$2.call(TransformTask.java:235)
                  at com.android.builder.profile.ThreadRecorder.record(ThreadRecorder.java:102)
                  at com.android.build.gradle.internal.pipeline.TransformTask.transform(TransformTask.java:230)
                  at sun.reflect.GeneratedMethodAccessor201.invoke(Unknown Source)
                  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
                  at java.lang.reflect.Method.invoke(Method.java:498)
                  at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73)
                  at org.gradle.api.internal.project.taskfactory.IncrementalTaskAction.doExecute(IncrementalTaskAction.java:50)
                  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.tasks.execution.ExecuteActionsTaskExecuter$1.run(ExecuteActionsTaskExecuter.java:131)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:300)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:292)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:174)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:90)
                  at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31)
                  at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:120)
                  at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:99)
                  at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:77)
                  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.api.internal.tasks.execution.EventFiringTaskExecuter$1.run(EventFiringTaskExecuter.java:51)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:300)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:292)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:174)
                  at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:90)
                  at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31)
                  at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:46)
                  at org.gradle.execution.taskgraph.LocalTaskInfoExecutor.execute(LocalTaskInfoExecutor.java:42)
                  at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareWorkItemExecutor.execute(DefaultTaskExecutionGraph.java:277)
                  at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareWorkItemExecutor.execute(DefaultTaskExecutionGraph.java:262)
                  at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:135)
                  at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:130)
                  at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker.execute(DefaultTaskPlanExecutor.java:200)
                  at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker.executeWithWork(DefaultTaskPlanExecutor.java:191)
                  at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$ExecutorWorker.run(DefaultTaskPlanExecutor.java:130)
                  at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
                  at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
                  at java.lang.Thread.run(Thread.java:748)
          [CIRCULAR REFERENCE:java.lang.ArrayIndexOutOfBoundsException]
  Caused by: java.lang.ArrayIndexOutOfBoundsException: 2
          at com.android.tools.r8.com.google.common.collect.RegularImmutableList.get(RegularImmutableList.java:60)
          at com.android.tools.r8.shaking.ProguardTypeMatcher$MatchTypePattern.matchClassOrTypeNameImpl(ProguardTypeMatcher.java:367)
          at com.android.tools.r8.shaking.ProguardTypeMatcher$MatchTypePattern.matchClassOrTypeNameImpl(ProguardTypeMatcher.java:394)
          at com.android.tools.r8.shaking.ProguardTypeMatcher$MatchTypePattern.matchClassOrTypeNameImpl(ProguardTypeMatcher.java:394)
          at com.android.tools.r8.shaking.ProguardTypeMatcher$MatchTypePattern.matches(ProguardTypeMatcher.java:334)
          at com.android.tools.r8.shaking.ProguardClassNameList$SingleClassNameList.matches(ProguardClassNameList.java:147)
          at com.android.tools.r8.shaking.RootSetBuilder.process(RootSetBuilder.java:205)
          at com.android.tools.r8.shaking.RootSetBuilder.lambda$runPerRule$4(RootSetBuilder.java:301)
  </code></pre>
  
  <p>I've not been able to find any real information on this, or general information on how to debug R8 errors so if someone could shed some light on this it would be greatly appreciated.</p>