Failure to resolve a package name when used together with other packages

[kvark]

Problem

In a modified Gecko project, doing cargo test -p foo -p bar fails to resolve one of the packages:
At the same time, doing cargo test -p foo and cargo test -p bar independently sees either package just fine.

kvark@ant /mnt/code/firefox/_webgpu $ cargo test -p qcms -p selectors -vv
    Updating git submodule `https://github.com/AOMediaCodec/av1-avif.git`
error: package ID specification `selectors` did not match any packages

kvark@ant /mnt/code/firefox/_webgpu $ cargo test -p qcms
   Compiling qcms v0.2.0 (/mnt/code/firefox/_webgpu/gfx/qcms)
...
kvark@ant /mnt/code/firefox/_webgpu $ cargo test -p selectors
   Compiling syn v1.0.73
...

Steps

1. Check out Gecko: git clone https://github.com/mozilla/gecko-dev
2. Add resolver = "2" to the root Cargo.toml
3. Run cargo test -p qcms -p selectors

Possible Solution(s)
I don't know why it fails to locate packages

Notes

Output of cargo version: cargo 1.53.0 (4369396ce 2021-04-27)

What I find especially sad here is the lack of any output. Even with "-vv" option and RUST_LOG=trace, cargo prints nothing before declaring that a package isn't found. It's just annoying/hard to debug this as a user.

[ehuss]

Hm, this is a bit tricky. The underlying issue is that selectors is not a workspace member. I think (at least for myself), I've not really considered the possibility of having local packages that aren't workspace members. Non-workspace members are usually registry dependencies, and cargo test -p foo of a registry dependency isn't a usual operation.

I think addressing this would start around here. The issue is that the "not a workspace member" fallback only triggers if you don't also include a workspace member. Somehow this needs to ensure that at least every spec is covered. Unfortunately including a non-member means you won't be able to specify any features.

As a workaround, I might suggest adding all local packages as workspace members.

[kvark]

Thank you for investigation! We have figured out the way to proceed, so this isn't blocking. But having no indication of what's going on was really annoying and time consuming. So fixing the error message in cargo to be clear would be ideal.