Mozilla has historically done some funky things with the Firefox Mercurial repositories. One of the things we've done is create a bunch of named branches to track the Firefox release process. These are branch names like GECKO20b12_2011022218_RELBRANCH.

Over in bug 927219, we started the process of cleaning up some cruft left over from many of these old branches.

For starters, the old named branches in the Firefox repositories are being actively closed. When you hg commit --close-branch, Mercurial creates a special commit that says this branch is closed. Branches that are closed are automatically hidden from the output of hg branches and hg heads. As a result, the output of these commands is now much more usable.

Closed branches still constitute heads on the DAG. And several heads lead to degraded performance in some situations (notably push and pull times - the same thing happens in Git). I'd like to eventually merge these old heads so that repositories only have 1 or a small number of DAG heads. However, extra care must be taken before that step. Stay tuned.

Anyway, for the average person reading, you probably won't be impacted by these changes at all. The greatest impact will be from the person who lands the first change on top of any repository whose last commit was a branch close. If you commit on top of the tip commit, you'll be committing on top of a previously closed branch! You'll instead want to hg up default after you pull to ensure you are on the proper DAG head! And even then, if you have local commits, you may not be based on top of the appropriate commit! A simple run of hg log --graph should help you decipther the state of the world. (Please note that the usability problems around discovering the appropriate head to land on are a result of our poor branching strategy for the Firefox repositories. We probably should have named branches tracking the active Gecko releases. But that ship sailed years ago and fixing that is pretty far down the priority list. Wallpapering over things with the firefoxtree extensions is my recommended solution until matters are fixed.)