title: Include scala classes in the sources jar generated by maven package
body: <p>The following plugin added to the <code>pom.xml</code> allows source-jar to be created when performing <code>mvn package</code>:</p>
  
  <pre><code>  &lt;plugin&gt;
      &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
      &lt;artifactId&gt;maven-source-plugin&lt;/artifactId&gt;
      &lt;executions&gt;
        &lt;execution&gt;
          &lt;id&gt;attach-sources&lt;/id&gt;
          &lt;goals&gt;
            &lt;goal&gt;jar&lt;/goal&gt;
          &lt;/goals&gt;
        &lt;/execution&gt;
      &lt;/executions&gt;
      &lt;/plugin&gt;
    &lt;/plugins&gt;
  </code></pre>
  
  <p>The usage of the <code>scala-maven-plugin</code> is :</p>
  
  <pre><code>  &lt;plugin&gt;
      &lt;groupId&gt;net.alchim31.maven&lt;/groupId&gt;
      &lt;artifactId&gt;scala-maven-plugin&lt;/artifactId&gt;
      &lt;version&gt;3.2.1&lt;/version&gt;
      &lt;executions&gt;
        &lt;execution&gt;
          &lt;goals&gt;
            &lt;goal&gt;compile&lt;/goal&gt;
            &lt;goal&gt;testCompile&lt;/goal&gt;
          &lt;/goals&gt;
        &lt;/execution&gt;
      &lt;/executions&gt;
      &lt;configuration&gt;
        &lt;jvmArgs&gt;
          &lt;jvmArg&gt;-Xmx12g&lt;/jvmArg&gt;
        &lt;/jvmArgs&gt;
        &lt;args&gt;
          &lt;arg&gt;-feature&lt;/arg&gt;
          &lt;arg&gt;-deprecation&lt;/arg&gt;
          &lt;arg&gt;-target:jvm-1.7&lt;/arg&gt;
        &lt;/args&gt;
      &lt;/configuration&gt;
    &lt;/plugin&gt;
  </code></pre>
  
  <p>However only the <code>java</code> sources are being included: the scala sources are left out.  Note that we are using the standard maven directory layout. In particular we have scala sources here:</p>
  
  <pre><code>  src/main/scala
  </code></pre>
  
  <p>So - are there additional options to the <code>maven-source-plugin</code> to encourage it to invite the scala classes to participate? Or a different scala-specific plugin and/or option to get them onboard?</p>