Java 8 nested lambdas break compiler

Question

i have a complex problem with Java 8.

Problem

With nested lambda compiler crash with a NullPointerException!

I know that lambdas must be stateless indeed in this case the codes that have state are Supplier implementations that however are anonymous classes and not lambdas.

Code

import java.util.function.Function;
import java.util.function.Supplier;

public class Test {

    public static Function<String, Supplier<String>> A = aVal -> new Supplier<String>() {

        @Override
        public String get() {
            return B.apply(aVal).get();
        }

        private Function<String, Supplier<String>> B = bVal -> new Supplier<String>() {
            @Override
            public String get() {
                return C.apply(bVal).get();
            }

            private Function<String, Supplier<String>> C = cVal -> new Supplier<String>() {
                @Override
                public String get() {
                    return cVal;
                }
            };
        };
    };
}

Stacktrace

An exception has occurred in the compiler (1.8.0_211). Please file a bug against the Java compiler via the Java bug reporting page (http://bugrepor
t.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report
. Thank you.
java.lang.NullPointerException
        at com.sun.tools.javac.jvm.Code.emitop0(Code.java:559)
        at com.sun.tools.javac.jvm.Items$SelfItem.load(Items.java:367)
        at com.sun.tools.javac.jvm.Gen.genArgs(Gen.java:966)
        at com.sun.tools.javac.jvm.Gen.visitApply(Gen.java:1842)
        at com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1465)
        at com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:947)
        at com.sun.tools.javac.jvm.Gen.visitAssign(Gen.java:1982)
        at com.sun.tools.javac.tree.JCTree$JCAssign.accept(JCTree.java:1686)
        at com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:947)
        at com.sun.tools.javac.jvm.Gen.visitExec(Gen.java:1781)
        at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1296)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:737)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:772)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:758)
        at com.sun.tools.javac.jvm.Gen.genStats(Gen.java:809)
        at com.sun.tools.javac.jvm.Gen.visitBlock(Gen.java:1157)
        at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:909)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:737)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:772)
        at com.sun.tools.javac.jvm.Gen.genMethod(Gen.java:1031)
        at com.sun.tools.javac.jvm.Gen.visitMethodDef(Gen.java:994)
        at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:778)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:737)
        at com.sun.tools.javac.jvm.Gen.genClass(Gen.java:2454)
        at com.sun.tools.javac.main.JavaCompiler.genCode(JavaCompiler.java:745)
        at com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1572)
        at com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1536)
        at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:901)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:860)
        at com.sun.tools.javac.main.Main.compile(Main.java:523)
        at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
        at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
        at org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.compileInProcess(JavaxToolsCompiler.java:125)
        at org.codehaus.plexus.compiler.javac.JavacCompiler.performCompile(JavacCompiler.java:171)
        at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:886)
        at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:129)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:154)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:146)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:81)
        at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
        at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:309)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:194)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:107)
        at org.apache.maven.cli.MavenCli.execute(MavenCli.java:955)
        at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:290)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:194)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)

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Tests

I did several attempts with different version(1.8.111, 1.8.152, 1.8.162, 1.8.211) and on different environment(Windows, Mac).

I tried with CMD using mvn clean compile or via intelliJ using maven plugin.

Removing function C all works fine.

---

My suppositions

hypothesis 1 This is a Java 8 limit and IntelliJ has a bug that allow me to collapse anonymous classes into lambdas though java 8 can't handle them.

hypothesis 2 This is a Java 8 bug.

I ask for your help for this interesting java problems. Thanks :)

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UPDATE

I've opened a bug on Java Bug Database. I've the confirm that this is a bug and it has been resolved on later version 9, 10, 11, etc...

https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8225771

Answer 1

It is a Java compiler bug¹. I can reproduce it with javac version 1.8.0_212 run from the command line. (No IDE's were used ... or harmed.)

The bug is not present in javac version 10.0.1, so upgrading your toolchain to Java 11 will fix the problem.

---

^{1 - Anything that causes the compiler to crash with an NPE is a bug!}