11/02/2016, 4:47 PM
It's idiomatic to omit the double-slash when possible. However it's required when referencing targets in the build root, so that the command-line parser can distinguish such targets from goal names: ./pants foo bar baz is ambiguous; ./pants foo //:bar //:baz is not. That said, it's not necessary, or even common, to have targets at the build root, and this practice is best avoided anyway.