The Eclipse JDT™ project provides the tool plug-ins that implement a Java IDE supporting the development of any Java application, including Eclipse plug-ins. It adds a Java project nature and Java perspective to the Eclipse Workbench as well as a number of views, editors, wizards, builders, and code merging and refactoring tools. The JDT project allows Eclipse to be a development environment for itself.
See also https://projects.eclipse.org/projects/eclipse.jdt and https://eclipse.org/eclipse
The Eclipse JDT project is split into multiple Git repositories, which are all part of this organization. If you face an issue and have a sense of which particular GitHub repository is most related, you can open your issue against that repository. If you're unsure, you can open an issue against this current repository and the issue will then be moved as best by maintainers.
Contributions are always welcome!
Please bear in mind that this project is almost entirely developed by volunteers. If you do not provide the implementation yourself (or pay someone to do it for you), the bug might never get fixed. If it is a serious bug, other people than you might care enough to provide a fix.