Small nit: Googles monorepo is based on Perforce.

I think what happened is Google bought a license for source code and customised it.

Yes, the server is based on Perforce, called Piper, but the CLI is based on mercurial. So locally you're doing hg and then when you create a CL, it translates it into what p4 needs.

	▲	surajrmal 2 hours ago \| parent [-]
		Depends on what frontend tool you use. You can use either. These days you can also use jj. I'm not sure the backend resembles peforce any longer.