Investigate Rust Rules

[jachris]

Investigate Rust Rules

[jachris]

It seems like it would be nice to integrate Cargo directly into the build. There is a related discussion going on at rust-lang/rust-roadmap-2017#12.

There are a many ways to do this. Without changes to the current code one might create a rule that executes cargo with CARGO_TARGET_DIR=<random temp dir> and move the produced files to the build directory. This however means that the entire project must be rebuilt every time there is a change, since the cargo state is deleted afterwards.

I came up with two solutions:

• Zip the entire cargo directory and unzip it when rebuilding. The published inputs would then be every file of the given directory containing the sources and cargo files. Expected outputs would probably be specified explicitly and copied after building.
• Just let cargo keep its state in the intermediate directory and resolve #7 by allowing not only output files, but output directories. These would be analyzed by Cook after the build and their state would be recorded to ensure correctness.

There is another problem related to cargo downlading the crates. This could be resolved by specifying the version of dependencies in Cargo.toml explicitly (using = x.y.z).