title: module-info.java compile fail with maven-compiler-plugin and automatic modules
body: <p>I'm using v3.7.0 of the plugin as required and JDK 9.0.1. I have added two <code>requires</code> statements, each referring to a jar in the class path (automatic module). The module-info.java compiles successfully in Eclipse after I moved the jars to Modulepath. However, Maven gives me a compiler error saying one of them is missing (strangely, not the first one which is just one line before). I tried to check the automatic module name but I get an error from the commands just for this jar. What does this error mean and how do I fix it so that I can discover the proper module name?</p>
  
  <p>I replaced my username in the output below. The jar in question does use a <code>ServiceLoader</code> but is not compiled with Java 9.</p>
  
  <pre><code>computerName:Commander-java username$ jar --file=/Users/username/.m2/repository/com/username/rcf/1.0/rcf-1.0.jar --describe-module
  Unable to derive module descriptor for: /Users/username/.m2/repository/com/username/rcf/1.0/rcf-1.0.jar
  Provider class com.username.rcf.server.TestCmdChain not in module
  
  computerName:Commander-java username$ java -p /Users/username/.m2/repository/com/username/rcf/1.0/rcf-1.0.jar --list-modules
  Error occurred during initialization of boot layer
  java.lang.module.FindException: Unable to derive module descriptor for /Users/username/.m2/repository/com/username/rcf/1.0/rcf-1.0.jar
  Caused by: java.lang.module.InvalidModuleDescriptorException: Provider class com.username.rcf.server.TestCmdChain not in module
  </code></pre>
  
  <p>The answer in <a href="https://stackoverflow.com/questions/46501388/how-to-deal-with-java-keywords-in-auto-generated-module-names-in-java-9">How to deal with java keywords in auto generated module names in Java 9?</a> has a different error related to using a Java identifier in the module name. The automatic jar name for my module should just be <code>rcf</code> since the jar name is <code>rcf-1.0.jar</code>. The error I'm getting is different also.</p>