How can I pass some compiler flags to certain crates?

[fCorleone]

Problem

I want to compile a project with cargo build. This project has one binary and several libraries. I would like to pass some compiler flags such as llvm-args=-sanitizer-coverage-level=2 to certain crates. If I change the environment variable: RUSTFLAGS, all the dependencies will also be passed with the flags. Is there a way?

Proposed Solution

No response

Notes

No response

[alexcrichton]

Currently there is no method of doing this, RUSTFLAGS applies to all crates. There is not a method to select flags for only some crates (except for the very last one through cargo rustc -- --custom-flag

[weihanglo]

The unstable profile rustflags feature can help this. For example

[profile.dev.package.foo]
opt-level = 3
rustflags = [ "-C", "..." ]

Let's track its progress over there #10271. Closing and thanks!