[Question] What does rust-analyzer expect in rust-project.json for "cyclic" dev-dependencies?

[googleson78]

Question

When we have a "cyclic" dependency of the form of X having itself as a dev-dependency (possibly transitively, e.g.
X -dev> A -> B -> X - see the reproducer below), what kind of data should I put in my rust-project.json so that it functions correctly? I know that rust-analyzer is able to handle this situation, because with a cargo based build, it works just fine - even the things inside X which really do depend on itself (or in my case depend on A).

EDIT: It seems I had a slip in my perception - it does not function correctly, i.e. in X (from the example above) I can't find out information regarding A (e.g. if I attempt to call a function from A I can't go to its definition or look at type information for it).

Context

The context is that right now, the rust-project.json generator in rules_rust can't handle a dependency of the form

rust_test(C) -> rust_library(A) -> rust_library(B) -> rust_library(C)

I'm trying to fix this, but I'm not sure what it should output in this case so that rust-analyzer can function correctly.

Reproducer

Here's a reproducer for the situation with both a Cargo and a Bazel based build.
In it, the dependency situation is as previously described,

C -dev> A -> B -> C

[flodiebold]

RA expects there to be no cyclic dependencies. This doesn't work with Cargo projects either. The 'correct' way of modeling this would be to have two separate crates in the graph for the two configurations of C (test and non-test), but we don't do this for Cargo projects either so I don't know how well it would work.

[googleson78]

I tried your suggestion by adding another crate in the graph (suffixed with _test) and that seems to work!

What's interesting is that it does even better than the "native" cargo solution in that I can now get information even inside the, which should theoretically have a circular dep 🤔

This makes me a bit doubtful that solution works in general, as my example is quite simple, and I could just be getting lucky. But I think it's definitely worth investigating, as if it does work in general, it might be an improvement for rust-analyzer overall.

Here's the the rust-project.json for reference.

Additionally, I only left the test tag from cfg in the _test crate, but it does not appear to matter, as even if I add it back to the original c crate, it doesn't break anything.