Clippy does not work with sccache set via RUSTC_WRAPPER

[thomaseizinger]

We are using sccache on Travis to minimize our build times. That works well for cargo build and cargo test.

However, it seems like cargo clippy is ignoring the set RUSTC_WRAPPER because it setting one by itself.

[matthiaskrgr]

I tried something like `RUSTC_WRAPPER="sccache clippy-driver rustc" but that did not work. 😄

[matthiaskrgr]

I made a ticket at the sccache repo: mozilla/sccache#423

[tylerhawkes]

I explored this a bit today and I couldn't get it to work even if I moved the rustc binary and placed a bash script that called it with sccache in its place. It appears this is something that clippy-driver needs to fix and honor the original RUSTC_WRAPPER when making its rustc calls.

I have a project that has over 600 build steps and 60% of the 20 minute build time is spent on 3 of them (which compile native code and are very cacheable). I know that clippy is compiling them because it says it is and when I run a cargo build afterward it finishes in 4 minutes and blows right past them, so getting this working with sccache would be a big win for me.