rustc version detection

[DemiMarie]

Currently, sccache is not aware of the version of rustc that it runs. Therefore, it is necessary to blow away the cache and start over after any Rust update.

[luser]

This is a duplicate of #87, should have been fixed by #666. In the general case, sccache includes a hash of the compiler binary (or libs in the rustc case) in the cache key, but that didn't work well with rustup. It should be fixed nowadays.

[DemiMarie]

Has the case of +nightly been fixed?

[froydnj]

Has the case of +nightly been fixed?

I believe it has; if you have evidence to the contrary of this, please file a separate bug.

[drahnr]

Edit: The sample shown here did not reproduce due to overlaying error of rust-lang/rust#73993 with the latest stable version, other tests with master did not yield any success either using drahnr/railcar and spearow/juice as test subject.

rm -rf target; cargo +nightly-2020-06-30 b --no-default-features --features=native; rm -rf target;  cargo +nightly-2020-07-02 b --no-default-features --features=native

work just fine with latest master.

Could we please slate a new release so the fix is contained in a release?

[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.