Although the daemon doesn't automatically build things. Buck does use watchman (https://github.com/facebook/watchman https://github.com/facebook/watchman) to w

Although the daemon doesn't automatically build things. Buck does use watchman (https://github.com/facebook/watchman https://github.com/facebook/watchman) to watch files though, and it has a way to run commands when files change: https://facebook.github.io/watchman/docs/watchman-make.html https://facebook.github.io/watchman/docs/watchman-make.html