Ok, I've looked this over and added some comments here and there, thanks @tomaka!

Could you also add some tests along these lines:

• build commands and cargo {test,run,bench,doc}
• propagating of -L throughout the entire dependency graph when one package requests it
• If I change a file in a package with a build command the build command is re-run

The list of things you plan on adding after this gets merged looks great, I hope to merge this soon! Some specific comments:

There's no feedback of the new system in the Compilation struct

This is currently mainly used for feeding information into cargo {test,bench,run} which uses the output of compilation to actually run some commands. I don't think we'll need to modify them much, but you'll need to be sure that any -L paths are indeed included in LD_LIBRARY_PATH.

The build directory is not used when determining the fingerprint, something that was apparently done for the native directory

Could you elaborate a little more on this?

Ah, and one other recommendation for tests: Could you pass -v wherever possible and match the entire output of all commands? I'd just want to make sure that build commands are printed as being run wherever possible.

Could you elaborate a little more on this?

I re-read Cargo's source code, and apparently I was mistaken. When I modified Layout, I noticed several references to native() in fingerprint.rs, but on a second look it's just here to fill the Compilation struct.

Ok, sounds good to me!

For the record, here's what remains to be done before merging:

• Extract code in cargo_rustc::compile to its own function
• Add tests for build commands and cargo {test,run,bench,doc}, don't forget the -v flag
• Add test for "If I change a file in a package with a build command the build command is re-run"
• Add tests for -l and -L flags being passed correctly (including -L between dependencies)