sccache does not realise that a rust compiler version has been changed by rustup

[aidanhs]

Specifically if doing rustup update nightly. This is probably because the path remains the same, and

An easy fix would just be to perform a single check of the mtime of some part of Rust every time when invoking the Rust compiler (being cautious that we're not checking the rustup wrapper binary).

[drahnr]

This is a duplicate of #853 and should be fixed by using the master branch beyond the merge of #666

[ryankurte]

is this compiler detection by any chance the cause of the following error with v0.2.13?

$ cargo +nightly build --target $TARGET --release $OPTIONS
error: failed to run `rustc` to learn about target-specific information
Caused by:
  process didn't exit successfully: `sccache rustc - --crate-name ___ --print=file-names --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=cfg` (exit code: 2)
  --- stderr
  error: failed to execute compile
  caused by: Failed to send data to or receive data from server
  caused by: Failed to read response header
  caused by: failed to fill whole buffer

not sure what has happened but somehow a CI image rebuild has broken sccache everywhere for us.

[drahnr]

@ryankurte v0.2.13 does not have channel/version detection rustc, you have to use the master branch for that.

I've never seen an error message before, please open a separate issue, it seems unrelated.

[glandium]

I'm going to close this issue as the problem is fixed on master. The remaining part is for the fix to make it to a release, which I'm going to cut before the end of year.