Maven compilation issue with Java 9

Question

Trying to compile a Maven project using JDK 9.0.1 I'm facing this stacktrace without much of an explanation:

Exception in thread "main" java.lang.AssertionError
at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
at jdk.compiler/com.sun.tools.javac.comp.Modules.enter(Modules.java:250)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.readSourceFile(JavaCompiler.java:821)
at jdk.compiler/com.sun.tools.javac.processing.JavacProcessingEnvironment$ImplicitCompleter.complete(JavacProcessingEnvironment.java:1510)
at jdk.compiler/com.sun.tools.javac.code.Symbol.complete(Symbol.java:633)
at jdk.compiler/com.sun.tools.javac.code.Symbol$ClassSymbol.complete(Symbol.java:1314)
at jdk.compiler/com.sun.tools.javac.code.Type$ClassType.complete(Type.java:1139)
at jdk.compiler/com.sun.tools.javac.code.Type$ClassType.getTypeArguments(Type.java:1065)
at jdk.compiler/com.sun.tools.javac.code.Printer.visitClassType(Printer.java:237)
at jdk.compiler/com.sun.tools.javac.code.Printer.visitClassType(Printer.java:52)
at jdk.compiler/com.sun.tools.javac.code.Type$ClassType.accept(Type.java:992)
at jdk.compiler/com.sun.tools.javac.code.Printer.visit(Printer.java:136)
at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArgument(AbstractDiagnosticFormatter.java:197)
at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArguments(AbstractDiagnosticFormatter.java:165)
at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:111)
at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:67)
at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArgument(AbstractDiagnosticFormatter.java:183)
at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArguments(AbstractDiagnosticFormatter.java:165)
at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:111)
at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:67)
at jdk.compiler/com.sun.tools.javac.util.JCDiagnostic.getMessage(JCDiagnostic.java:771)
at jdk.compiler/com.sun.tools.javac.api.ClientCodeWrapper$DiagnosticSourceUnwrapper.getMessage(ClientCodeWrapper.java:799)
at org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.compileInProcess(JavaxToolsCompiler.java:131)
at org.codehaus.plexus.compiler.javac.JavacCompiler.performCompile(JavacCompiler.java:174)
at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:1075)
at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:168)
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:993)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:345)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:191)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
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)

Not really sure what's causing this, is this a bug in the JDK?

Additional details:

• Maven 3.5.0 with maven-compiler-plugin 3.7.0
• I'm just executing mvn clean install
• The source code is not open source unfortunately, so I'm not at liberty to share it
• There are no module-info.java files yet, I'm just trying to compile a project using Java 9
• Strangely enough if I leave the source level on 1.8, the code compiles, but it fails with the above exception if I specify it as 9

Answer 1

Just add this

<forceJavacCompilerUse>true</forceJavacCompilerUse>

to your maven compiler build plugin in your POM and you'll see all the javac errors! Source with more details