Cabal used to be hosted in a darcs repository with an accompanying Trac for bugs and a wiki. However, the popularity of github was too much to resist, and the project was moved to git some time in April 2012 (cf. 16ed5a5a).
The issues were imported en masse. Unfortunately, the issue numbers didn't quite match up, so cross-references were broken. However, they're normally fewer than 10 apart, and each original Trac ID is included in the imported tickets, so it's generally possible to find what you were looking for by manually tweaking the ticket number.
The wiki was not mass-imported, but what looked relevant has been copied over here page-by-page. There's an oddity in that I changed Pandoc versions mid-way through the import, so some things are in a slightly different style from others.
I've divided the imported pages into the following (purely provisional) categories: