Integrate Kotlin with generated Java Classes

Question

We use an annotation processing framework (Immutables) to generate Java classes from interfaces.

Now I have to access these generated classes from a kotlin class. While in Java this works well, the Kotlin compiler cannot find them.

Here is the maven configuration:

        <plugin>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-plugin</artifactId>
            <version>${kotlin.version}</version>
            <executions>
                <execution>
                    <id>compile</id>
                    <phase>compile</phase>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                    <configuration>
                        <sourceDirs>
                            <sourceDir>${project.basedir}/src/main/java</sourceDir>
                        </sourceDirs>
                    </configuration>
                </execution>
                <execution>
                    <id>test-compile</id>
                    <phase>test-compile</phase>
                    <goals>
                        <goal>test-compile</goal>
                    </goals>
                    <configuration>
                        <sourceDirs>
                            <sourceDir>${project.basedir}/src/test/java</sourceDir>
                        </sourceDirs>
                    </configuration>
                </execution>
            </executions>
        </plugin>

        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <executions>
                <!-- Replacing default-compile as it is treated specially by maven -->
                <execution>
                    <id>default-compile</id>
                    <phase>none</phase>
                </execution>
                <!-- Replacing default-testCompile as it is treated specially by maven -->
                <execution>
                    <id>default-testCompile</id>
                    <phase>none</phase>
                </execution>
                <execution>
                    <id>java-compile</id>
                    <phase>compile</phase>
                    <goals> <goal>compile</goal> </goals>
                </execution>
                <execution>
                    <id>java-test-compile</id>
                    <phase>test-compile</phase>
                    <goals> <goal>testCompile</goal> </goals>
                </execution>
            </executions>
        </plugin>

Kotlin version is 1.2.10 (but it's the same with 1.2.20). Swapping the plugin declarations did not help. How can I configure this?

Answer 1

The Kotlin compiler runs before the Java compiler. To have the created classes available with Kotlin, you have to use kapt and define every annotation processor there.

<execution>
    <id>kapt</id>
    <goals>
        <goal>kapt</goal>
    </goals>
    <configuration>
        <sourceDirs>
            <sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
            <sourceDir>${project.basedir}/src/main/java</sourceDir>
        </sourceDirs>
        <annotationProcessorPaths>
            <annotationProcessorPath>
                <groupId>org.immutables</groupId>
                <artifactId>value</artifactId>
                <version>2.5.5</version>
            </annotationProcessorPath>
        </annotationProcessorPaths>
    </configuration>
</execution>