[maven] How to configure multi-module Maven + Sonar + JaCoCo to give merged coverage report?

I found another solution for new Sonar versions where JaCoCo's binary report format (*.exec) was deprecated and the preferred format is XML (SonarJava 5.12 and higher). The solution is very simple and similar to the previous solution with *.exec reports in parent directory from this topic: https://stackoverflow.com/a/15535970/4448263.

Assuming that our project structure is:

moduleC - aggregate project's pom
  |- moduleA - some classes without tests
  |- moduleB - some classes depending from moduleA and tests for classes in both modules: moduleA and moduleB

You need following maven build plugin configuration in aggregate project's pom:

<plugin>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>0.8.5</version>
    <executions>
        <execution>
            <id>prepare-and-report</id>
            <goals>
                <goal>prepare-agent</goal>
                <goal>report</goal>
            </goals>
        </execution>
        <execution>
            <id>report-aggregate</id>
            <phase>verify</phase>
            <goals>
                <goal>report-aggregate</goal>
            </goals>
            <configuration>
                <outputDirectory>${project.basedir}/../target/site/jacoco-aggregate</outputDirectory>
            </configuration>
        </execution>
    </executions>
</plugin>

Then build project with maven:

mvn clean verify

And for Sonar you should set property in administration GUI:

sonar.coverage.jacoco.xmlReportPaths=target/site/jacoco/jacoco.xml,../target/site/jacoco-aggregate/jacoco.xml

or using command line:

mvn sonar:sonar -Dsonar.coverage.jacoco.xmlReportPaths=target/site/jacoco/jacoco.xml,../target/site/jacoco-aggregate/jacoco.xml

Description

This creates binary reports for each module in default directories: target/jacoco.exec. Then creates XML reports for each module in default directories: target/site/jacoco/jacoco.xml. Then creates an aggregate report for each module in custom directory ${project.basedir}/../target/site/jacoco-aggregate/ that is relative to parent directory for each module. For moduleA and moduleB this will be common path moduleC/target/site/jacoco-aggregate/.

As moduleB depends on moduleA, moduleB will be built last and its report will be used as an aggregate coverage report in Sonar for both modules A and B.

In addition to the aggregate report, we need a normal module report as JaCoCo aggregate reports contain coverage data only for dependencies.

Together, these two types of reports providing full coverage data for Sonar.

There is one little restriction: you should be able to write a report in the project's parent directory (should have permission). Or you can set property jacoco.skip=true in root project's pom.xml (moduleC) and jacoco.skip=false in modules with classes and tests (moduleA and moduleB).