Assuming crates b-g aren't dependent on crate a, if they already started building cargo will wait for them to finish, but cargo won't start compiling any other crates. If the crates are dependent on a, they can't be built if a can't. As far as I'm aware, there is no option to force cargo to build every crate it can. I personally would suggest making liberal use of the todo! or similar tricks to ensure that crate a can build.