.gitignore file is not copied to archetype JAR - Workarounds?

The bug is now fixed in the maven-resources-plugin.

To include the .gitignore file, the maven-resources-plugin plugin should be set explicitly in the archetype pom.xml file with the configuration value addDefaultExcludes set to false:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-resources-plugin</artifactId>
  <version>3.0.2</version>
  <configuration>
    <addDefaultExcludes>false</addDefaultExcludes>
  </configuration>
</plugin>

As @amanteaux says, adding addDefaultExcludes with false ensures that the maven-resources-plugin copies the .gitignore file to target/classes, however, maven-jar-plugin (> 2.4) won't copy .gitignore to the resulting jar. See this stackoverflow comment for more information. So one workaround would be, in addition to the flag above for maven-resources-plugin, rollback maven-jar-plugin to 2.4.