SCCACHE not caches same crate for different component

[soloturn]

Problem

am using

 CARGO_TARGET_DIR=/tmp/mytarget  RUSTC_WRAPPER=sccache cargo ... 

for 2 components, on linux. the cache works quite well when compiling a component again. but when compiling the second component it fails. both comonents have approximately 600 crates, most of them same version. so download into CARGO_HOME is done only one time for 95% of the crates. compile is 2 times 600, 100% cache miss.

Steps

❯ rm -rf ~/.cargo/
❯ rm -rf ~/.cache/sccache/
❯ git clone --filter=blob:none git@github.com:pop-os/cosmic-comp.git
❯ git clone --filter=blob:none git@github.com:pop-os/cosmic-session.git
❯ cd cosmic-comp
❯ RUSTUP_TOOLCHAIN=stable RUSTFLAGS="-C link-arg=-fuse-ld=mold" CARGO_TARGET_DIR=/tmp/mytarget RUSTC_WRAPPER=sccache cargo vendor 
  Downloaded 628 crates (108.5 MB) in 2m 14s (largest was `windows` at 11.8 MB)
❯ RUSTUP_TOOLCHAIN=stable RUSTFLAGS="-C link-arg=-fuse-ld=mold" CARGO_TARGET_DIR=/tmp/mytarget RUSTC_WRAPPER=sccache cargo build --release --frozen --offline

❯ rm -rf /tmp/mytarget
❯ RUSTUP_TOOLCHAIN=stable RUSTFLAGS="-C link-arg=-fuse-ld=mold" CARGO_TARGET_DIR=/tmp/mytarget RUSTC_WRAPPER=sccache cargo build --release --frozen --offline

❯ sccache --show-stats
Compile requests                   1138
Compile requests executed           892
Cache hits                          405
Cache hits (Rust)                   405
Cache misses                        477


❯ cd cosmic-session
❯ RUSTUP_TOOLCHAIN=stable RUSTFLAGS="-C link-arg=-fuse-ld=mold" CARGO_TARGET_DIR=/tmp/mytarget RUSTC_WRAPPER=sccache cargo vendor 
  Downloaded 100 crates (12.0 MB) in 13.63s
❯ RUSTUP_TOOLCHAIN=stable RUSTFLAGS="-C link-arg=-fuse-ld=mold" CARGO_TARGET_DIR=/tmp/mytarget RUSTC_WRAPPER=sccache cargo build --release --frozen --offline
    Building [============>            ] 104/189: rustix, futures-util, tracing-subscriber, tokio                                                                                                                                           

during compile one can check the cache state
``
❯ sccache --show-stats
Compile requests 86
Compile requests executed 51
Cache hits 0
Cache misses 45
Cache misses (Rust) 45

### Possible Solution(s)

_No response_

### Notes

_No response_

### Version

_No response_

[epage]

As expressed in other threads, this is not a Cargo bug or feature request but a support request for a third-party tool, sccache.

Please either reach out to sccache through their means or the wider Rust community at https://users.rust-lang.org/

[soloturn]

this is a cargo flag, would be strange if this would not be in cargo then.

[epage]

Its a cargo flag that allows you to plug third-party programs into Cargo. What those third-party programs do is not up to Cargo which is the intent of a flag like this.