cargo rustc for passing arbitrary flags to rustc

cargo rustc is a new subcommand for Cargo that allows you to pass arbitraryrustc flags through Cargo.

For example, Cargo does not have a way to pass unstable flags built-in. Butif we'd like to use print-type-sizes to see what layout information ourtypes have, we can run this:

$ cargo rustc -- -Z print-type-sizes

And we'll get a bunch of output describing the size of our types.

Note

cargo rustc only passes these flags to invocations of your crate, and not to any rustcinvocations used to build dependencies. If you'd like to do that, see $RUSTFLAGS.