Manifest to fetch every Apache Maven git repositories using Google repo.
In addition, an aggregator structure is provided to build everything as one aggregated build.
mkdir maven
cd maven
repo init -u https://gitbox.apache.org/repos/asf/maven-sources.git
repo sync
repo start master --all
Then simply use the cloned content with normal git commands.
Once content is cloned with previous instructions, you can build each repository as a separate project.
You can also build absolutely everything in one aggregated run (WARNING: more than 400 modules...):
cd sources
mvn --fail-at-end -Prun-its verify
mvn --fail-at-end -Preporting site
See Maven Sources Overview description.