--extern Options
The behavior of the --extern flag can be modified with noprelude, priv or nounused options.
This is unstable feature, so you have to provide -Zunstable-options to enable it.
Examples
Use your own build of the core crate.
rustc main.rs -Z unstable-options --extern noprelude:core=libcore.rlib
To use multiple options, separate them with a comma:
rustc main.rs -Z unstable-options --extern noprelude,priv,nounused:mydep=mydep.rlib
Options
noprelude: Do not add the crate to the external prelude. If used, it will need to be imported usingextern crate. This is used by the build-std project to simulate compatibility with sysroot-only crates.priv: Mark the crate as a private dependency for theexported_private_dependencieslint.nounused: Suppressunused-crate-dependencieswarnings for the crate.