Consider using profiles to simplify manual configuration for Maven builds

[olafurpg]

The following configuration can be added to pom.xml to configure lsif-java

 <profile>
          <id>lsif-java</id>
          <dependencies>
            <dependency>
              <groupId>com.sourcegraph</groupId>
              <artifactId>semanticdb-javac</artifactId>
              <version>0.5.6</version>
              <scope>provided</scope>
            </dependency>
          </dependencies>
          <build>
            <plugins>
              <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                  <compilerArgs>
                    <arg>-Xplugin:semanticdb -sourceroot:${session.executionRootDirectory} -targetroot:${session.executionRootDirectory}/target/semanticdb-targetroot</arg>
                  </compilerArgs>
                </configuration>
              </plugin>
            </plugins>
          </build>
        </profile>
      </profiles>
    </project>

The command mvn -Plsif-java -DskipTests clean verify will then produce SemanticDB files. The benefit of this approach is that it's possible to commit this change to pom.xml. The lsif-java dependency is only added when the command-line flag -Plsif-java is enabled.

The downside of this approach:

• the semanticdb-javac dependency version is hardcoded and needs to be kept up-to-date
• it doesn't seem possible to add profiles via settings.xml, which would make it possible for lsif-java index to automatically use profiles instead of the custom javac executable approach