Anyone wishing to contribute to AspectJ should check out the README hosted on the AspectJ GitHub Project. In particular there is a contribution guide that discusses how to get setup with a development environment for AspectJ and run the tests (and write new ones). Please raise issues in the GitHub project
The build process for AspectJ uses GitHub Actions to drive regular builds of master and for test runs against any submitted PRs.
You can use the code from these repositories to experiment, test, build, create patches, issue pull requests, etc.