Cargo and some dependencies are compiled twice on CI

[alexcrichton]

I noticed on the most recently timed out mipsel dist builder that Cargo, the library, was compiled twice. This is no small chunk of time!

Investigating it looks like a number of libraries were compiled at least twice, including: cargo, chrono, crates-io, docopt, env_logger, failure_derive, failure, num, serde_derive_internals, serde_derive, synstructure.

My guess is that the feature selection is changing for deeply nested crates like syn or num between top-level targets like the RLS and Cargo. We should make sure that the feature selection is the same so the dependencies can be shared, and then we should probably add a check to CI that Cargo isn't compiled twice.

[alexcrichton]

cc @Mark-Simulacrum, @kennytm

[ishitatsuyuki]

I think I brought up this before, and as a result you closed the issue at Cargo side.

[alexcrichton]

Cargo is working as intended, our CI is not

[ishitatsuyuki]

So this is rust-lang/cargo#4048. I think this is definitely a feature worth implement in Cargo.

[alexcrichton]

I think this will be fixed with nrc/derive-new#28 and #48642

[alexcrichton]

Fixed in #48642