Hi Shaimaa!
Thank you for your interest in iBugs. The repository contains several versions of AspectJ in a subversion repository. To checkout a specific version, you have to use the build.xml file provided in the repository. Please take a look at the README file in the root folder, it contains all the information. The AspectJ source code is split into several project src folders. For example, to checkout version 28919 run
ant -DfixId=28919 checkoutversion
Make sure that version directory "version" exists in the root folder of the subject. Then you can find the sources of the weaver in "org.aspectj/modules/weaver/src".
Regards,
Valentin