Exception While Using net.alchim31.maven:scala-maven-plugin - scala

Question

I have a scala-maven-spark project.
Here is my pom.xml file
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
<scala.version>2.11.8</scala.version>
</properties>
<dependencies>
<dependency>
<groupId>org.scalatest</groupId>
<artifactId>scalatest_2.11</artifactId>
<version>3.0.2</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-sql_2.11</artifactId>
<version>2.4.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>28.1-jre</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api-scala_2.11</artifactId>
<version>11.0</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.17.0</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>2.17.0</version>
</dependency>
</dependencies>
<build>
<sourceDirectory>src/main/scala</sourceDirectory>
<testSourceDirectory>src/test/scala</testSourceDirectory>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.7</version>
<configuration>
<skipTests>true</skipTests>
</configuration>
</plugin>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.3.3</version>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
</configuration>
</plugin>
<plugin>
<groupId>org.scalatest</groupId>
<artifactId>scalatest-maven-plugin</artifactId>
<version>1.0</version>
<configuration>
<reportsDirectory>${project.build.directory}/surefire-reports</reportsDirectory>
<junitxml>.</junitxml>
<filereports>WDF TestSuite.txt</filereports>
</configuration>
<executions>
<execution>
<id>test</id>
<goals>
<goal>test</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.2.1</version>
<executions>
<!-- Run shade goal on package phase -->
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<createDependencyReducedPom>false</createDependencyReducedPom>
<filters>
<filter>
<artifact>*:*</artifact>
<excludes>
<exclude>META-INF/*.SF</exclude>
<exclude>META-INF/*.DSA</exclude>
<exclude>META-INF/*.RSA</exclude>
</excludes>
</filter>
</filters>
<finalName>${project.artifactId}-${project.version}</finalName>
<relocations>
<relocation>
<pattern>com.google.protobuf</pattern>
<shadedPattern>shaded.com.google.protobuf</shadedPattern>
</relocation>
<relocation>
<pattern>com.google.common</pattern>
<shadedPattern>shaded.com.google.common</shadedPattern>
</relocation>
</relocations>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
When I run mvn clean package I am getting the below error
[ERROR] Failed to execute goal net.alchim31.maven:scala-maven-plugin:3.3.3:compile (default) on project decisionengine-data-ingestion-maven: wrap: org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
If I remove the net.alchim31.maven plugin the build completes successfully.
Error details
[ERROR] error: scala.reflect.internal.MissingRequirementError: object java.lang.Object in compiler mirror not found.
[ERROR] at scala.reflect.internal.MissingRequirementError$.signal(MissingRequirementError.scala:17)
[ERROR] at scala.reflect.internal.MissingRequirementError$.notFound(MissingRequirementError.scala:18)
[ERROR] at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:53)
[E

Answer 1

If you have scala source code you need
to add the scala-maven-plugin (please use a more recent version see https://search.maven.org/search?q=a:scala-maven-plugin, today 4.5.6 is the latest, why using 3.3.3 from 2018-06 ?) to compile your code
to have the scala-library as an explicit dependency
And remove
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
</configuration>
It's better to let the plugin detects the scala version from dependencies.