`ClassCastException` in JSpecify mode when generics and arrays are involved

[JarvisCraft]

Description

When using the latest NullAway (0.12.15) in JSpecify mode, ClassCastException occurs while handling array types with null-marking at generic positions.

Minimal reproducible example

Code:

import java.util.function.Function;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

@NullMarked
class MinExample {

    void use(AsyncTask<AsyncTask<@Nullable Void>[]> tasks) {
        tasks.flatMap(readyTasks -> consume(readyTasks));
        //           ^
    }


    interface AsyncTask<T extends @Nullable Object> {
        <U extends @Nullable Object> AsyncTask<U> flatMap(
            Function<T, ? extends AsyncTask<U>> mapper
        );
    }

    AsyncTask<@Nullable Void> consume(AsyncTask<@Nullable Void>[] tasks) {
        throw new UnsupportedOperationException("TODO");
    }
}

Expected behaviour: successful compilation.

Actual behaviour: javac crash

Stacktace

MinExample.java:9: error: An unhandled exception was thrown by the Error Prone static analysis plugin.
        tasks.flatMap(readyTasks -> consume(readyTasks));
                     ^
     Please report this at https://github.com/google/error-prone/issues/new and include the following, as well as a reproducing code sample (if possible):
  
     error-prone version: 2.45.0
     BugPattern: NullAway
     Stack Trace:
     java.lang.ClassCastException: class com.sun.tools.javac.code.Type$TypeVar cannot be cast to class com.sun.tools.javac.code.Type$ArrayType (com.sun.tools.javac.code.Type$TypeVar and com.sun.tools.javac.code.Type$ArrayType are in module jdk.compiler of loader 'app')
  	at com.uber.nullaway.generics.CheckIdenticalNullabilityVisitor.visitArrayType(CheckIdenticalNullabilityVisitor.java:101)
  	at com.uber.nullaway.generics.CheckIdenticalNullabilityVisitor.visitArrayType(CheckIdenticalNullabilityVisitor.java:17)
  	at jdk.compiler/com.sun.tools.javac.code.Type$ArrayType.accept(Type.java:1378)
  	at com.uber.nullaway.generics.CheckIdenticalNullabilityVisitor.visitClassType(CheckIdenticalNullabilityVisitor.java:77)
  	at com.uber.nullaway.generics.CheckIdenticalNullabilityVisitor.visitClassType(CheckIdenticalNullabilityVisitor.java:17)
  	at jdk.compiler/com.sun.tools.javac.code.Type$ClassType.accept(Type.java:1056)
  	at com.uber.nullaway.generics.GenericsChecks.identicalTypeParameterNullability(GenericsChecks.java:1099)
  	at com.uber.nullaway.generics.GenericsChecks.subtypeParameterNullability(GenericsChecks.java:1130)
  	at com.uber.nullaway.generics.GenericsChecks.lambda$compareGenericTypeParameterNullabilityForCall$0(GenericsChecks.java:1264)
  	at com.uber.nullaway.InvocationArguments.forEach(InvocationArguments.java:86)
  	at com.uber.nullaway.generics.GenericsChecks.compareGenericTypeParameterNullabilityForCall(GenericsChecks.java:1235)
  	at com.uber.nullaway.NullAway.handleInvocation(NullAway.java:2003)
  	at com.uber.nullaway.NullAway.matchMethodInvocation(NullAway.java:444)
  	at com.google.errorprone.scanner.ErrorProneScanner.processMatchers(ErrorProneScanner.java:539)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethodInvocation(ErrorProneScanner.java:888)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethodInvocation(ErrorProneScanner.java:178)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1876)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)
  	at jdk.compiler/com.sun.source.util.TreeScanner.visitExpressionStatement(TreeScanner.java:504)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitExpressionStatement(ErrorProneScanner.java:775)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitExpressionStatement(ErrorProneScanner.java:178)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1655)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scan(TreeScanner.java:110)
  	at jdk.compiler/com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:271)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitBlock(ErrorProneScanner.java:621)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitBlock(ErrorProneScanner.java:178)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1148)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:95)
  	at jdk.compiler/com.sun.source.util.TreeScanner.visitMethod(TreeScanner.java:223)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethod(ErrorProneScanner.java:882)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethod(ErrorProneScanner.java:178)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:992)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:95)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scan(TreeScanner.java:110)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:118)
  	at jdk.compiler/com.sun.source.util.TreeScanner.visitClass(TreeScanner.java:202)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitClass(ErrorProneScanner.java:649)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitClass(ErrorProneScanner.java:178)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:899)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scan(TreeScanner.java:110)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:118)
  	at jdk.compiler/com.sun.source.util.TreeScanner.visitCompilationUnit(TreeScanner.java:151)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitCompilationUnit(ErrorProneScanner.java:661)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitCompilationUnit(ErrorProneScanner.java:178)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:627)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:66)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:58)
  	at com.google.errorprone.scanner.ErrorProneScannerTransformer.apply(ErrorProneScannerTransformer.java:43)
  	at com.google.errorprone.ErrorProneAnalyzer.finished(ErrorProneAnalyzer.java:231)
  	at jdk.compiler/com.sun.tools.javac.api.MultiTaskListener.finished(MultiTaskListener.java:133)
  	at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1423)
  	at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1370)
  	at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:955)
  	at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl.lambda$doCall$0(JavacTaskImpl.java:104)
  	at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl.invocationHelper(JavacTaskImpl.java:152)
  	at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:100)
  	at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:94)
  	at org.gradle.internal.compiler.java.IncrementalCompileTask.call(IncrementalCompileTask.java:92)
  	at org.gradle.api.internal.tasks.compile.AnnotationProcessingCompileTask.call(AnnotationProcessingCompileTask.java:94)
  	at org.gradle.api.internal.tasks.compile.ResourceCleaningCompilationTask.call(ResourceCleaningCompilationTask.java:57)
  	at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:83)
  	at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:50)
  	at org.gradle.api.internal.tasks.compile.daemon.AbstractIsolatedCompilerWorkerExecutor$CompilerWorkAction.execute(AbstractIsolatedCompilerWorkerExecutor.java:79)
  	at org.gradle.workers.internal.DefaultWorkerServer.execute(DefaultWorkerServer.java:68)
  	at org.gradle.workers.internal.AbstractClassLoaderWorker$1.create(AbstractClassLoaderWorker.java:54)
  	at org.gradle.workers.internal.AbstractClassLoaderWorker$1.create(AbstractClassLoaderWorker.java:48)
  	at org.gradle.internal.classloader.ClassLoaderUtils.executeInClassloader(ClassLoaderUtils.java:100)
  	at org.gradle.workers.internal.AbstractClassLoaderWorker.executeInClassLoader(AbstractClassLoaderWorker.java:48)
  	at org.gradle.workers.internal.FlatClassLoaderWorker.run(FlatClassLoaderWorker.java:32)
  	at org.gradle.workers.internal.FlatClassLoaderWorker.run(FlatClassLoaderWorker.java:22)
  	at org.gradle.workers.internal.WorkerDaemonServer.run(WorkerDaemonServer.java:108)
  	at org.gradle.workers.internal.WorkerDaemonServer.run(WorkerDaemonServer.java:77)
  	at org.gradle.process.internal.worker.request.WorkerAction.lambda$run$1(WorkerAction.java:150)
  	at org.gradle.process.internal.worker.child.WorkerLogEventListener.withWorkerLoggingProtocol(WorkerLogEventListener.java:41)
  	at org.gradle.process.internal.worker.request.WorkerAction.lambda$run$2(WorkerAction.java:150)
  	at org.gradle.internal.operations.CurrentBuildOperationRef.with(CurrentBuildOperationRef.java:84)
  	at org.gradle.process.internal.worker.request.WorkerAction.run(WorkerAction.java:142)
  	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
  	at java.base/java.lang.reflect.Method.invoke(Method.java:565)
  	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
  	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
  	at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:182)
  	at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:164)
  	at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:414)
  	at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
  	at org.gradle.internal.concurrent.AbstractManagedExecutor$1.run(AbstractManagedExecutor.java:47)
  	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
  	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
  	at java.base/java.lang.Thread.run(Thread.java:1474)

Related problem

Originally, the signature of flatMap was PECSified, i.e.:

        <U extends @Nullable Object> AsyncTask<U> flatMap(
            Function<? super T, ? extends AsyncTask<U>> mapper
        );

which did not cause a crash but did cause a false positive with the code above:

MinExample.java:9: error: [NullAway] incompatible types: AsyncTask<Void> [] cannot be converted to AsyncTask<@Nullable Void> []
          tasks.flatMap(readyTasks -> consume(readyTasks));
                                              ^
      (see http://t.uber.com/nullaway )
  1 error

which also seems invalid(?) (although I may be misreading the spec).

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🔗 Similar Issues

Related Issues

• JSpecify: report unboxing warning for for-each loop over array of @Nullable Integer, etc. #1275
• In JSpecify mode, Generic<Void> is not accepted as a subtype of Generic<@Nullable Void> #1172
• JSpecify: missing warning with inner classes and inheritance #1274
• Unhandled NullPointerException with intersection bounds on generic field #1377
• Missing Generics causes: java.lang.RuntimeException: Number of types arguments in Foo.Supplier<java.lang.Object> does not match Foo.Supplier #1151
• Exception when have workaround because type erasure on JVM #1264
• java.lang.ClassCastException: class com.sun.tools.javac.tree.JCTree$JCNewClass cannot be cast to class com.sun.source.tree.MethodInvocationTree #1138

🔗 Related PRs

#1248 - Better handle calls to super constructors and superclass methods in JSpecify mode [merged]
#1309 - Use refined types from dataflow analysis in generic method inference [merged]
#1332 - Enable the VoidMissingNullable checker and autofix all extant warnings [merged]
#1345 - Support marking method type variable upper bounds as @Nullable in library models [merged]
#1375 - Run dataflow analysis on bodies of lambdas passed to generic methods [merged]

👤 Suggested Assignees

• msridhar
• agrieve
• Stephan202
• HildingLinden
• kingg22

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💬 Have feedback or questions? Drop into our discord!

[JarvisCraft]

Thanks a lot for this and #1417 fix!

[msridhar]

Thanks for the reports @JarvisCraft! The test cases made reproducing easy. Please let us know if you run into further issues.

[msridhar]

BTW for your related problem could you file a separate issue if that is still happening? @JarvisCraft

[JarvisCraft]

Please let us know if you run into further issues.

Just ran 0.13.0-SNAPSHOT (built from master) on our project, can confirm that the issue is fixed.

BTW for your related problem could you file a separate issue if that is still happening?

Interestingly, both non-PECS and PECS variants are now fine (not false-positively reported) thus there is no need for a separate issue.