I only skimmed through the documentation, so I must have missed something, but I fail to see how it can be better than either redo[0] or tup[1] in either speed or dependency tracking.
shrug Haven't messed with redo or tup. Maybe they do great dependency tracking as well. It's not a new idea. Pants is basically a copy of Google's build system by a bunch of ex-Googlers.
Pants also does nifty things like artifact caching between members of a team which is nice.
It will continue to do more nice things in the future as it's under active development by a decent number of people at this point.
tup does perfect instantaneous dependency tracking: It monitors file system access to see which files were accessed during build (you don't have to tell it). It does not depend on tool co-operation, and it's the only build system that will figure out that you've upgraded your compiler (e.g. if javac or gcc was replaced) and thus a rebuild is in order.
redo is explicit; it doesn't automatically do dependency tracking, you have to tell it what went it. But it's fast and incredibly elegant - it's extremely easy to make it track any dependencies you know about, and it's built for easily rebuilding just a part of your system.
