(Worked at google for 2-3 years, under google3 depot) - AFAIK, only few hundreth files are not visible to employees, and certain folks (contractors) maybe limit

(Worked at google for 2-3 years, under google3 depot) - AFAIK, only few hundreth files are not visible to employees, and certain folks (contractors) maybe limited there too. You can actually compile, and run in dev/staging certain things, inspect code, click on function, and see callsites, even "debug" from the browser (debugging, is pretty much, if your binary have stepped through a bookmark, then it'll tell you, and you may print out locals from the scope - like vars, etc. - hard to explain in short). Then "checking out", to put in p4/svn - is not really like that - but you can find pretty much videos, docs explaining it. It's more like - you create a "workspace", "client" (piper has history from p4, so some terms are similar to perforce), and in this client - you "view" the entire depot, and changes you've made are "overlayed". Then you can submit these in a CL (much like perforce). There is also git (git5) and hg mode, but I've never used them. I've used the "CitC" one (client in the cloud), and was great as I was able to edit, and later edit, even build,... even deploy all from the browser (though prefer real IDE there - like Eclipse/IntelliJ/CLion).