title: fatal error compiling invalid flag --module-path
body: <p>I have a <a href="https://github.com/lapots/java-cloud-sample" rel="noreferrer">project</a>. Originally it was a single module project with structure like this</p>
  
  <pre><code>java-cloud-sample\
      src\
          main\
              java
      pom.xml
  </code></pre>
  
  <p>I decided to make it into a multi-module structure - I use <code>java 9</code> anyway. 
  So I separated it like this</p>
  
  <pre><code>java-cloud-sample\
      java-cloud-rest-api\
          src\
          pom.xml
      pom.xml
  </code></pre>
  
  <p>Where root <code>pom.xml</code> looks like this</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"&gt;
      &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt;
  
      &lt;groupId&gt;com.lapots.breed.platform.cloud&lt;/groupId&gt;
      &lt;artifactId&gt;java-cloud-sample&lt;/artifactId&gt;
      &lt;version&gt;0.0.1-SNAPSHOT&lt;/version&gt;
      &lt;packaging&gt;pom&lt;/packaging&gt;
  
      &lt;modules&gt;
          &lt;module&gt;java-cloud-rest-api&lt;/module&gt;
      &lt;/modules&gt;
  
      &lt;parent&gt;
          &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
          &lt;artifactId&gt;spring-boot-starter-parent&lt;/artifactId&gt;
          &lt;version&gt;1.5.6.RELEASE&lt;/version&gt;
      &lt;/parent&gt;
  
      &lt;properties&gt;
          &lt;project.build.sourceEncoding&gt;UTF-8&lt;/project.build.sourceEncoding&gt;
          &lt;project.reporting.outputEncoding&gt;UTF-8&lt;/project.reporting.outputEncoding&gt;
          &lt;maven.compiler.source&gt;1.9&lt;/maven.compiler.source&gt;
          &lt;maven.compiler.target&gt;1.9&lt;/maven.compiler.target&gt;
      &lt;/properties&gt;
  
      &lt;build&gt;
          &lt;plugins&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
                  &lt;artifactId&gt;maven-compiler-plugin&lt;/artifactId&gt;
                  &lt;version&gt;3.6.2&lt;/version&gt;
              &lt;/plugin&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
                  &lt;artifactId&gt;maven-jar-plugin&lt;/artifactId&gt;
                  &lt;version&gt;3.0.0&lt;/version&gt;
              &lt;/plugin&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
                  &lt;artifactId&gt;maven-dependency-plugin&lt;/artifactId&gt;
                  &lt;version&gt;3.0.1&lt;/version&gt;
                  &lt;executions&gt;
                      &lt;execution&gt;
                          &lt;id&gt;copy-dependencies&lt;/id&gt;
                          &lt;phase&gt;package&lt;/phase&gt;
                          &lt;goals&gt;&lt;goal&gt;copy-dependencies&lt;/goal&gt;&lt;/goals&gt;
                      &lt;/execution&gt;
                  &lt;/executions&gt;
              &lt;/plugin&gt;
          &lt;/plugins&gt;
      &lt;/build&gt;
  
  
  &lt;/project&gt;
  </code></pre>
  
  <p>And module <code>pom.xml</code> looks like this</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"&gt;
      &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt;
  
      &lt;parent&gt;
          &lt;groupId&gt;com.lapots.breed.platform.cloud&lt;/groupId&gt;
          &lt;artifactId&gt;java-cloud-sample&lt;/artifactId&gt;
          &lt;version&gt;0.0.1-SNAPSHOT&lt;/version&gt;
      &lt;/parent&gt;
  
      &lt;artifactId&gt;java-cloud-rest-api&lt;/artifactId&gt;
      &lt;description&gt;Demo project for Spring Boot&lt;/description&gt;
      &lt;packaging&gt;jar&lt;/packaging&gt;
  
      &lt;dependencies&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
              &lt;artifactId&gt;spring-boot-starter-actuator&lt;/artifactId&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
              &lt;artifactId&gt;spring-boot-starter-web&lt;/artifactId&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
              &lt;artifactId&gt;spring-boot-starter-data-jpa&lt;/artifactId&gt;
          &lt;/dependency&gt;
  
          &lt;dependency&gt;
              &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
              &lt;artifactId&gt;spring-boot-devtools&lt;/artifactId&gt;
              &lt;scope&gt;runtime&lt;/scope&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;com.h2database&lt;/groupId&gt;
              &lt;artifactId&gt;h2&lt;/artifactId&gt;
              &lt;scope&gt;runtime&lt;/scope&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;org.postgresql&lt;/groupId&gt;
              &lt;artifactId&gt;postgresql&lt;/artifactId&gt;
              &lt;scope&gt;runtime&lt;/scope&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
              &lt;artifactId&gt;spring-boot-starter-test&lt;/artifactId&gt;
              &lt;scope&gt;test&lt;/scope&gt;
          &lt;/dependency&gt;
      &lt;/dependencies&gt;
  
      &lt;build&gt;
          &lt;plugins&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
                  &lt;artifactId&gt;spring-boot-maven-plugin&lt;/artifactId&gt;
                  &lt;executions&gt;
                      &lt;execution&gt;
                          &lt;goals&gt;
                              &lt;goal&gt;build-info&lt;/goal&gt;
                          &lt;/goals&gt;
                          &lt;configuration&gt;
                              &lt;additionalProperties&gt;
                                  &lt;encoding.source&gt;${project.build.sourceEncoding}&lt;/encoding.source&gt;
                                  &lt;encoding.reporting&gt;${project.reporting.outputEncoding}&lt;/encoding.reporting&gt;
                                  &lt;java.source&gt;${maven.compiler.source}&lt;/java.source&gt;
                                  &lt;java.target&gt;${maven.compiler.target}&lt;/java.target&gt;
                              &lt;/additionalProperties&gt;
                          &lt;/configuration&gt;
                      &lt;/execution&gt;
                  &lt;/executions&gt;
              &lt;/plugin&gt;
          &lt;/plugins&gt;
      &lt;/build&gt;
  &lt;/project&gt;
  </code></pre>
  
  <p>But when I try to run <code>mvn clean package</code> I get </p>
  
  <pre><code>INFO] java-cloud-rest-api ................................ FAILURE [  1.060 s]
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD FAILURE
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time: 2.104 s
  [INFO] Finished at: 2017-09-08T17:15:46+03:00
  [INFO] Final Memory: 27M/331M
  [INFO] ------------------------------------------------------------------------
  [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.6.2:compile (default-compile) on project java-cloud-rest-api: Fatal error compiling: invalid flag: --module-path -&gt; [Help 1]
  [ERROR]
  [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
  [ERROR] Re-run Maven using the -X switch to enable full debug logging.
  [ERROR]
  [ERROR] For more information about the errors and possible solutions, please read the following articles:
  [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
  [ERROR]
  [ERROR] After correcting the problems, you can resume the build with the command
  [ERROR]   mvn &lt;goals&gt; -rf :java-cloud-rest-api
  </code></pre>
  
  <p>What is the problem? (maybe I should split <code>maven</code> project into separate modules and each maven module split into <code>java</code> modules)</p>