On Thu, May 30, 2013 at 05:56:43PM -0700, Johnny Stenback wrote: > [TL;DR, I think we need to embrace git in addition to hg for > Firefox/Gecko hacking, what do you think?] > > Hello everyone, > > The question of whether Mozilla engineering should embrace git usage for > Firefox/Gecko development has come up a number of times already in > various contexts, and I think it's time to have a serious discussion > about this. > > To me, this question has already been answered. Git is already a reality > at Mozilla: > > 1. Git is in use exclusively for some of our significant projects (B2G, > Gaia, Rust, Servo, etc) > 2. Lots of Gecko hackers use git for their work on mozilla-central, > through various conversions from hg to git. > > What we're really talking about is whether we should embrace git for > Firefox/Gecko development in mozilla-central. > > IMO, the benefits for embracing git are: > > * Simplified on-boarding, most of our newcomers come to us > knowing git (thanks to Github etc), few know hg. > * We already mirror hg to git (in more ways than one), and > git is already a necessary part of most of our lives. > Having one true git repository would simplify developers' > lives. > * Developers can use git branches. They just work, > and they're a good alternative to patch queues. > * Developers can benefit from the better merge algorithms > used by git. > * Easier collaboration through shared branches. > * We could have full history in git, including all of hg > and CVS history since 1998! > * Git works well with Github, even though we're not switching > to Github as the ultimate source of truth (more on that below). > > Some of the known issues with embracing git are: > > * Performance of git on windows is sub-optimal (we're > already working on it). > * Infrastructure changes needed... > > So in other words, I think there's significant value in embracing git > and I think we should make it easier to hack on Gecko/Firefox with git. > I see two ways to do that: > > 1: Embrace both git and hg as a first class DVCS. > 2: Switch wholesale to git. > > Option 1 is where I personally think it's worth investing effort. It > means we'd need to set up an atomic bidirectional bridge between hg and > git (which I'm told is doable, and there are even commercial solutions > for this out there that may solve this for us). Assuming we solve the > bridge problem one way or another, it would give us all the benefits > listed above, plus developer tool choice, and we could roll this out > incrementally w/o the need to change all of our infrastructure at once. > I.e. our roll out could look something like this: > > 1. create a read only, official mozilla-central git mirror > 2. add support for pushing to try with git and see the results in tbpl > 3. update tbpl to show git revisions in addition to hg revisions > 4. move to project branches, then inbound, then m-c, release branches, etc
Another way to look at this would be to make the git repository the real central source, and keep the mercurial branches as clones of it, with hg-git (and hg-git supports pushing to git, too). This would likely make it easier to support pushing to both, although we'd need to ensure nobody pushes octopus merges in the git repo. > Option 2 is where this discussion started (in the Tuesday meeting a few > weeks ago, > https://wiki.mozilla.org/Platform/2013-05-07#Should_we_switch_from_hg_to_git.3F). > Since then I've had a number of conversations and have been convinced > that a wholesale change is the less attractive option. The cost of a > wholesale change will be *huge* on the infrastructure end, to a point > where we need to question whether the benefits are worth the cost. I > have also spoken with other large engineering orgs about git performance > limitations, one of which is doing the opposite switch, going from git > to hg. I bet this is facebook. Their usecase includes millions of changesets with millions of files (iirc, according to posts i've seen on the git list). Mike _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
