Building for host architecture and then another target invalidates cache

[ryanbai1412]

Problem

1. Run cargo build and wait for the build to finish
2. Run cargo build --target <target triple> for a few seconds
3. Run cargo build again, the build restarts from scratch

I would expect step 3 to not rebuild from scratch and instead use the cached artifacts produced in step 1.

Steps

No response

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.62.0 (a748cf5a3 2022-06-08)
release: 1.62.0
commit-hash: a748cf5a3e666bc2dcdf54f37adef8ef22196452
commit-date: 2022-06-08
host: x86_64-unknown-linux-gnu
libgit2: 1.4.2 (sys:0.14.2 vendored)
libcurl: 7.80.0-DEV (sys:0.4.51+curl-7.80.0 vendored ssl:OpenSSL/1.1.1n)
os: Ubuntu 22.04 (jammy) [64-bit]

[ehuss]

Thanks for the report! Can you please provide a complete reproduction? That shouldn't happen, and I'm unable to reproduce it with a typical project.

[ryanbai1412]

In my .cargo/config.toml I have:

[target.x86_64-unknown-linux-gnu]
linker = "clang" 
rustflags = ["-C", "link-arg=-fuse-ld=/usr/local/bin/mold"]

Without the above cargo works as expected. A simpler version of the config.toml would be something like:

[target.x86_64-unknown-linux-gnu]
rustflags = ["-O"]

Also I should mention that cargo build --target x86_64-unknown-linux-gnu (my host) instead of cargo build caches with other targets.

[ehuss]

Ah, specifying rustflags will indeed cause a difference here. There are two points:

• Without --target, the rustflags are not picked up from the implicit host target. target-applies-to-host changes this behavior.
• Cargo does not support multiple cached artifacts with different rustflags settings. Reconsider RUSTFLAGS artifact caching. #8716 contains some more context.

[willhodges]

@ehuss I'm seeing this issue with multiple build targets and the same non-default RUSTFLAGS across those targets.

[willhodges]

This is still an issue.

[ehuss]

Closing as a duplicate of the two issues linked above. This is just something that cargo does not support at this time.