D's bug database is currently a Bugzilla instance located at https://issues.dlang.org/. It is hosted and maintained by Brad Roberts.
Although it is good practice to include direct links to issues in GitHub pull requests, here is a UserScript which automatically turns "issue NNNN" text on GitHub pages of D projects into links to the corresponding Bugzilla page:
To quickly access a certain Bugzilla issue or search the database, you can create a browser search as follows:
- Open Bugzilla
- Right-click the "Search" field at the top
- Select "Create search" (or your browser's equivalent).
Depending on your web browser, you can assign a keyword (e.g. "db" for "D Bugs"), which should allow opening any issue by typing "db NNNN" in the location bar. Searching works in the same way, by entering search terms instead of NNNN.