Remote: do not create http repository if it already exists.

[damienmg]

Using native.existing_rules allow to use several crates.bzl file that
would import the same crates without failing with duplicate rules.

[acmcarther]

Sync w/ master should fix your build (your other CL was merged).

Can you share a little bit more detail about the use case that motivated this change? I see that, mechanically speaking, it lets you combine several crates.bzl files. This sounds fine to me, but I'm also interested to hear what kind of situation led to needing several crates.bzl files....

[damienmg]

Rebased.

It's not something I encountered with raze yet but it something that happens all the time in other similar tools. The classic use case is I include libA and libB, both use cargo raze and both wrap the repositories in a bzl file exposed to the people. So you call liba_repositories() and llibb_repositories() and you get a collisions.

[acmcarther]

I'm really nervous thinking about users having multiple cargo-raze resolved crate sets in the same workspace, but in reality this is just fixing a bug that someone will inevitably run into.

I'm thinking that ultimately "library-like" workspaces will need a way to express their third party crate dependencies, and a root workspace will need a mechanism to supply them. The prior art here isn't very encouraging.