AFAIK, Google's g4 is the successor to p4 (perforce), and it uses monotonically increasing number ("CL") instead of hash. From what I can remember, it was one w

AFAIK, Google's g4 is the successor to p4 (perforce), and it uses monotonically increasing number ("CL") instead of hash. From what I can remember, it was one way to specify a build - e.g. this binary was build with CL=12345 (baseline) + cherry picks (e.g. locally checked out) CL's 123450, 123455, 123460 - hence one would always know where it's in the timeline of things based on just this number.