Fix cargo registry caching for builds

[bjorn3]

#3612 (comment)

[bjorn3]

Windows still has the caching issue. There is some work being done over at https://github.com/openethereum/openethereum/pull/11568 to fix this, but it doesn't work yet.

[matklad]

Hm, do we really need this?

Looking at https://github.com/rust-analyzer/rust-analyzer/runs/510919657?check_suite_focus=true#step:8:1, it seems like caching works as expected?

[bjorn3]

https://github.com/rust-analyzer/rust-analyzer/runs/510919657?check_suite_focus=true#step:5:13 shows errors though.

[matklad]

Yeah... That probably means that we don't need to cache the registry at all? We cache compiled libraries anyway.

[bjorn3]

Maybe

[bjorn3]

It is useful when updating rustc, as in that case all crates need to be recompiled.

[matklad]

I think if we are recompiling the world, saving on network doesn't really make sense. I'd just remove this from caching then!

[matklad]

bors r+

Thanks!

Let's see how it works out...

[bjorn3]

I think I should have kept the Cache cargo index step.

[matklad]

yeah, r+ doesn't mean anything anyway, this has to be merged manually...

[bjorn3]

Forgot that gh apps can't merge workflow changes.

[bjorn3]

Seems that the cargo registry cache is actually necessary: https://github.com/rust-analyzer/rust-analyzer/pull/3613/checks?check_run_id=511843473#step:7:12