[FIXED] Include scala classes in the sources jar generated by maven package

Issue

The following plugin added to the pom.xml allows source-jar to be created when performing mvn package:

  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-source-plugin</artifactId>
    <executions>
      <execution>
        <id>attach-sources</id>
        <goals>
          <goal>jar</goal>
        </goals>
      </execution>
    </executions>
    </plugin>
  </plugins>

The usage of the scala-maven-plugin is :

  <plugin>
    <groupId>net.alchim31.maven</groupId>
    <artifactId>scala-maven-plugin</artifactId>
    <version>3.2.1</version>
    <executions>
      <execution>
        <goals>
          <goal>compile</goal>
          <goal>testCompile</goal>
        </goals>
      </execution>
    </executions>
    <configuration>
      <jvmArgs>
        <jvmArg>-Xmx12g</jvmArg>
      </jvmArgs>
      <args>
        <arg>-feature</arg>
        <arg>-deprecation</arg>
        <arg>-target:jvm-1.7</arg>
      </args>
    </configuration>
  </plugin>

However only the java 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:

  src/main/scala

So - are there additional options to the maven-source-plugin to encourage it to invite the scala classes to participate? Or a different scala-specific plugin and/or option to get them onboard?

Solution

The jar goal of the Maven Source Plugin will bundle all of the sources of the Maven project into a JAR. You can select what to include or exclude in those source folders (with the includes and excludes parameters), but you cannot add whole new source folders to it; they must be added as source folders of the Maven project itself.

When you have a pure Scala project, src/main/scala and src/test/scala are declared as source folders, because you would have:

<sourceDirectory>src/main/scala</sourceDirectory>
<testSourceDirectory>src/test/scala</testSourceDirectory>

in your POM, overriding the default src/main/java and src/test/java. So the Maven Source Plugin would correctly add the sources present in those two folders without additional configuration.

But when you have a mixed Java / Scala project, the <sourceDirectory> and <testSourceDirectory> element are typically left in to their default values. This does not create any problems with regard to compiling or running Scala code with the plugin, as it looks up the files by default in ${project.build.sourceDirectory}/../scala. However, other unrelated Maven plugins can't know about those new folders.

To fix this, the plugin provides the add-source goal, which adds src/main/scala and src/test/scala as source and test source directory to the Maven project, and, thus, makes them available for the other plugins relying on the source directories, like the Maven Source Plugin. You should therefore change your POM to:

<plugin>
  <groupId>net.alchim31.maven</groupId>
  <artifactId>scala-maven-plugin</artifactId>
  <version>3.2.1</version>
  <executions>
    <execution>
      <goals>
        <goal>add-source</goal>
        <goal>compile</goal>
        <goal>testCompile</goal>
      </goals>
    </execution>
  </executions>
  <!-- rest of configuration -->
</plugin>

Answered By - Tunaki
Answer Checked By - Marie Seifert (JavaFixing Admin)