How many lines of code did Google's main source-code repository contain, per the figure Google disclosed in 2015?

Answer

2,000,000,000 lines of code

Nearly all of Google lives in one giant shared repository — roughly 40 times the size of the Windows codebase by Wired's comparison — absorbing tens of thousands of code changes every day.

Source: Google (Potvin & Levenberg, Communications of the ACM 2016; Wired 2015)