Note that extensions that ship with Mercurial are exactly as supported as the tool itself, and come with the same kinds of backwards compatibility guarantees. It's not worth worrying about rebase, histedit, and record being extensions - if you want them, turn them on and use them.
They're not exactly as supported, because they're not on by default, and they're not the thing everyone in the Mercurial culture tells you to use as the obvious solution to problems. Version control is as much about what other people do as what you do, and what other people do tends to align most closely with the defaults and what the tools encourage.
No, they're exactly as supported. What I meant by that was that we promise to not break them, ever, to keep the output formats stable, and accept bug reports for them. That doesn't necessarily mean it's something we'll always recommend (eg mq isn't something I'd recommend for a new user, rebase/histedit/amend are way better and always will be.)
We don't turn them on by default for two reasons: newbie users not shooting their foot off unexpectedly, and UI clutter. mq alone (which we actually recommend avoiding now if you don't really need it) adds a bunch of verbs to the command line interface.
We've talked about having an 'hg hello' command or something that'd give you a proposed template hgrc that suggest you might want rebase/record/histedit/pager/color/progress, but nobody's worked out exactly what that should be like. Does something like that sound like it might be helpful?
Some people like it, but my basic complaint with it is that it introduces a new concept, the "patch", that is basically a crippled commit. When a patch is not a commit, you get rejected diff hunks when it fails to apply, and it can easily forget its history.
An MQ patch is basically a commit that doesn't know how to merge and doesn't keep backups. It's way too easy to make a mistake and lose work. I consider MQ one of hg's youthful mistakes before tools like histedit, rebase, and Evolve came to exist.
mq keeps its patches as an internal per-repo stack. This is much weaker than git's tree branches.
Here's an example: let's say I've been working on a repo, and have 2 current mq patches called A and B pushed. There's no way for me to pop A and B, then apply another patch called D in the current repo (at least as far as I could figure out). Also, even if there were, I'd have no way of then pushing A and B on top of D. The patches only work as a linear stack (D must come on top of B).
It's a very powerful tool, but also a complex one, and one which brings in a bunch of new commands. There are a bunch of extension which provide nice UIs to various subsets of mq's full power, and are much simpler.
If you need mq, use mq, but if you just need to e.g. do some history edition, use histedit.
> They're not exactly as supported, because they're not on by default
I really don't get this. In almost any software there are features that are not 'on by default', but it's still implemented and supported (except explicitly stated otherwise). How can this be a reason to not use the functionality when you need it?
It's like using Outlook to respond to mail on a mailing list. Sure, it's theoretically possible to use some combination of manual configuration and extra work to construct a post that won't violate social norms, but the tool doesn't encourage it, so mailing lists with a significant number of Outlook users on them tend to fail to follow the standard mailing list conventions of other lists, and develop their own conventions.
The same holds for any tool used in a workflow that involves anyone other than yourself: any tool with a default workflow tends to encourage people to follow that default workflow.
The fact they are not on by default seems to actually be hurting Mercurial in the debate against Git. As every review of "Mercurial vs Git" assumes they are not available, just because they are not enabled in default configuration out of the box.
Maybe Mercurial should start shipping them enabled?
I would rather they be made easier to enable (currently one has to edit an .INI file). That would be better than trying to appease some hypothetical from-Git converts.
