This is an issue extracted from the discussion over at rust-lang/rust-roadmap-2017#12. The general high-level idea is that Cargo should be able to produce a build plan for the explicit purpose of consumption by another tool. This step would not iteslf execute any work but will likely assume that all the source code is available for consumption.

Once Cargo is able to support this it should be explored to see what this integration would then look like into external build system, such as Buck or Bazel. This may involve writing generators which translates from Cargo's build plan to a Buck/Bazel configuration file, or it may involve more dynamism at build time.

The goal here is to leverage Cargo as much as possible for drawing dependencies between projects and learning how the compiler is executed. This should give us quite a bit of flexibility to continue to implement new features in Cargo (such as the recently stabilized proc-macro) with little-to-no changes in external build tools.