Add generated java sources to mixed scala-java project

I am currently working on a project where I want to generate an ANTLR parser from a grammar and continue working with that parser inside my Scala code.

For this, I set up a new project with the following POM file:

<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>foo</groupId>
  <artifactId>bar</artifactId>
  <version>1.0-SNAPSHOT</version>
  <name>${project.artifactId}</name>
  <description>Foo</description>

  <properties>
    <maven.compiler.source>1.6</maven.compiler.source>
    <maven.compiler.target>1.6</maven.compiler.target>
    <encoding>UTF-8</encoding>
    <scala.version>2.11.5</scala.version>
    <scala.compat.version>2.11</scala.compat.version>
    <antlr.version>4.7</antlr.version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.scala-lang</groupId>
      <artifactId>scala-library</artifactId>
      <version>${scala.version}</version>
    </dependency>
    <dependency>
      <groupId>org.antlr</groupId>
      <artifactId>antlr4-runtime</artifactId>
      <version>${antlr.version}</version>
    </dependency>

    <!-- Test -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.specs2</groupId>
      <artifactId>specs2-core_${scala.compat.version}</artifactId>
      <version>2.4.16</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.scalatest</groupId>
      <artifactId>scalatest_${scala.compat.version}</artifactId>
      <version>2.2.4</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <build>
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>net.alchim31.maven</groupId>
          <artifactId>scala-maven-plugin</artifactId>
          <version>3.2.1</version>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>2.0.2</version>
        </plugin>
        <plugin>
          <groupId>org.antlr</groupId>
          <artifactId>antlr4-maven-plugin</artifactId>
          <version>${antlr.version}</version>
        </plugin>
      </plugins>
    </pluginManagement>
    <plugins>
      <plugin>
        <groupId>net.alchim31.maven</groupId>
        <artifactId>scala-maven-plugin</artifactId>
        <executions>
          <execution>
            <id>scala-compile-first</id>
            <phase>process-resources</phase>
            <goals>
              <goal>add-source</goal>
              <goal>compile</goal>
            </goals>
          </execution>
          <execution>
            <id>scala-test-compile</id>
            <phase>process-test-resources</phase>
            <goals>
              <goal>testCompile</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <executions>
          <execution>
            <phase>compile</phase>
            <goals>
              <goal>compile</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.18.1</version>
        <configuration>
          <useFile>false</useFile>
          <disableXmlReport>true</disableXmlReport>
          <!-- If you have classpath issue like NoDefClassError,... -->
          <!-- useManifestOnlyJar>false</useManifestOnlyJar -->
          <includes>
            <include>**/*Test.*</include>
            <include>**/*Suite.*</include>
          </includes>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.antlr</groupId>
        <artifactId>antlr4-maven-plugin</artifactId>
        <executions>
          <execution>
            <id>antlr</id>
            <goals>
              <goal>antlr4</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <visitor>true</visitor>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Compiling a project with a grammar file in the default location works just fine - Java sources are generated to target/generated-sources/antlr as expected.

However, I can not import the generated parser (let's call it FooParser) inside my Scala code - IntelliJ recognizes that there is something called FooParser but when I try to auto-import it, it fails.

Also, building from the command line with mvn compile with source code depending on the FooParser fails.

Resolution of the whole thing was rather dumb: My file structure was wrong:

src/
  main/
    antlr/
      Foo.g4

You have to put your grammars into proper packages, otherwise the whole thing wont be properly 'importable'.

src/
  main/
    antlr/
      packagename/
        Foo.g4