`cargo build` and `cargo test` always expire each other build cache

bug

very common scenario let build cache expired

version

1.80.0

edit

• was able to always reproduce this, before I cargo clean

• after cargo clean, cannot reproduce this again

actual

N th build is expected.

$ cargo build --profile xxx && yarn workspaces foreach --all run postbuild
...
255.36s user 15.29s system 110% cpu 4:04.42 total

N+1 th build are also expected.

$ cargo build --profile xxx && yarn workspaces foreach --all run postbuild
...
15.90s user 1.18s system 100% cpu 16.910 total

$ cargo build --profile xxx && yarn workspaces foreach --all run postbuild
...
15.27s user 1.11s system 104% cpu 15.685 total

$ cargo build --profile xxx && yarn workspaces foreach --all run postbuild
...
15.65s user 1.07s system 104% cpu 16.081 total

BUT unexpectedly, cargo test seems expire all cache.

$ cargo test --profile xxx
...
391.13s user 24.45s system 114% cpu 6:04.12 total

Below cargo test are expected.

$ cargo test --profile xxx
...
0.66s user 0.39s system 16% cpu 6.182 total

$ cargo test --profile xxx
...
0.45s user 0.23s system 122% cpu 0.555 total

Unexpectedly, cargo build expire cargo test cache.

$ cargo build --profile xxx && yarn workspaces foreach --all run postbuild
...
247.31s user 15.54s system 110% cpu 3:58.70 total

$ cargo build --profile xxx && yarn workspaces foreach --all run postbuild
...
15.57s user 1.04s system 103% cpu 16.054 total

expected

• cargo test should not expire cargo build cache.

• cargo build should not expire cargo test cache.

• should have rust docs on how to improve compile speed beside sccache

additional

I always see compiling all the dep tree again and again and again and again and again.

• Are there any solution or workaround to pre compile all the libraries?

Start by reproducing the alternating cargo build --profile xxx and cargo test --profile xxx commands, recording whether each command recompiles the dependency tree. Compare the build-cache behavior before and after cargo clean; done means repeated build and test runs reuse the expected artifacts without invalidating each other, with any documentation scope separately identified.