Is cargo check necessary in buildDepsOnly?

[szlend]

I've been wondering why cargo check is necessary in buildDepsOnly. It adds quite a bit to the compilation time as you're basically compiling the deps twice (cargo check + cargo build).

There's a comment in buildDepsOnly.nix saying:

# First we run `cargo check` to cache cargo's internal artifacts, fingerprints, etc. for all deps.
# Then we run `cargo build` to actually compile the deps and cache the results

However I tried disabling the cargo check step and the dep caching still appears to work fine and I didn't notice any dependencies being recompiled in the buildPackage step. Is it safe to disable this or will I eventually run into problems? I think it's worth leaving a comment with some more context, like specific instances where this is necessary.

[dpc]

Might be wrong, but the "check" part might be needed for clippy and cargo doc. So if someone doesn't need them they might want to skip cargo check on deps.

[szlend]

I can confirm that it's definitely necessary for caching cargo clippy. We have separate debug/release builds, with debug builds being used for checks so I think it should be fine to disable this for our release builds.