wtf is sapling?

Sapling SCM is a replacement for Git that's designed to handle truly massive repositories without slowing down. While Git can struggle when a codebase contains millions of files or commits, Sapling stays fast because it only needs to think about the files you're actually working with, not the entire repository history. If you work at a large company with a huge shared codebase, or you're building infrastructure that serves many teams, Sapling is built to handle that scale. The system works by separating concerns: your local computer runs the Sapling client (a command-line tool called sl), which talks to a server called Mononoke and uses a virtual filesystem called EdenFS to manage what files actually live on your disk. Instead of downloading and storing everything, EdenFS brings files to your machine on demand as you need them, like a smart cache that keeps operations quick even in repos with millions of files. The README notes that this does come with a tiny performance cost the first time you access a new file, but that tradeoff is worth it when you're working in a massive codebase and most developers only touch a small slice of it. You'd use Sapling if you're coming from Git and work in a large-scale environment where Git has become a bottleneck. The project is designed to feel familiar to Git users, it's command-line driven and can work with existing Git repositories. It even includes an interactive web interface called Interactive Smartlog (ISL) that lets you visualize and manage your commits through a browser or VS Code, which can be easier than memorizing command-line flags. It's worth noting that Sapling is built by Meta (Facebook's parent company) and used internally there, but the open-source version has some limitations. The client-side tools are fully available, but Mononoke (the server component) and EdenFS (the virtual filesystem) don't currently build or run publicly, so you can't set up the full system yourself yet. For now, the open-source release is most useful if you want to try the client tools or if you're contributing to the project.