JJ is useful for those of us who understand the shittiness of Git but have to work in a world that got locked into path dependent network effects by VC money.
> When I left Google three years ago I recall they were trying to figure out what to do about either making Git scale, or adopting Mercurial, or what.
Rarely had to consult the docs for weird edge cases and generally operation felt natural and seamless. It was easy to onboard new devs of all experience levels.
I switched to git 5 years back and I still feel lost sometimes and inadvertently end up in detached head state once in a while. Git feels really "unnatural" or "unintuitive" to me in some way that Mercurial never did (I can't put my finger on why because I never gave Mercurial much thought).
While working on a stack of changes, you should be able to check out an earlier commit, amend it, and have its descendants be automatically rebased. Of course you should be able to -- this is a natural and straightforward way to think about working on changes, and builds on prior knowledge about how to work with individual commits and how to rebase them onto a newer upstream. Now compare this to git rebase -i.
if you take the time to learn it, the underlying data model for git makes sense, leading to the tools making sense, for those that put in the time investment to understand the underlying data model. This meant that there was a bunch of git expertise floating around IRC and mailing lists. Git tooling also wasn't super opinionated, letting pre-git workflows be run on git with little modification (which is also its problem, but does drive adoption). Sure, a recommended workflow has emerged, but that came later. By the time GitHub started in 2008, that was three years after its invention and use on the Linux kernel and git already had the mindshare and intertia. Without VC funding, GitLab or BitBucket or even Google Code might be the dominant platform, but it really was git's speed and fast branching, and proven scalability from managing Linux kernel development that led to git's rise as the preferred solution. (Its inability to handle monorepos like Google/Meta wasn't an issue for that time.)
Mercurial's lack of speed and inflexibility are what hurt adoption. VC money pouring in might have saved it, by somehow addressing those two issues, but unfortunately we'll never know. Mercurial's workflow is pretty central though so I doubt its community would have supported changes to the central workflow. Moving from Subversion to a DVCS (aka mercurial/hg or git) required learning a new tool and being forced to change workflow on top of that made the decision to go with git easier since a git expert could make a company-specific cheat sheet that didn't also require learning and adapting to a new way of working at the same time.
Most of the world was on SVN by the time git came around, and Git-svn was a pretty popular adapter. You could use git and its fast local branching before the company turned to git. I really can't stress the fast local branching enough as a reason for git winning. SVN server-side branches took forever to be created (even with the underlying data not actually being copied) and I remember even just running "hg" and no arguments being slow.
VC funding helped GitHub, but git still would have won out because hg didn't have a dev community to rival the Linux Kernel. Maybe Wikipedia/Wikimedia, but that's a much smaller codebase.
This was definitely a really big complaint. Python's just slow to start up, and last I checked Python 3 makes things even worse here.
Startup time really made me believe that the optimal language to write CLI tools is Rust.
It ended on a bitter note when Microsoft bought them, sure. But let's not rewrite history, GitHub was not dumped on the market by deep-pocketed VCs. GitHub was self-funded from 2007 to 2012, at which point it was wildly popular and used a big cash injection to get to where it is now. By the time that happened it had the #1 position in commits per month and was about to become #1 in repos hosted also.
[0] https://en.wikipedia.org/wiki/Distributed_version_control#Hi...