Leftover rust-analyzer specs can cause generation to fail #2774

I ran into a odd situation where after running bazel run @rules_rust//tools/rust_analyzer:gen_rust_project I got an error

Error: Failed to make progress on building crate dependency graph

However, I was confused because on a different machine (same code and commit) the tool worked just fine. After running

RUST_LOG=debug bazel run @rules_rust//tools/rust_analyzer:gen_rust_projec

and diffing logs from the working machine and broken machine, I noticed the working machine had

[WARN gen_rust_project_lib::aquery] Skipping missing crate_spec file: ....

but the broken machine didn't have this log and instead had

[DEBUG gen_rust_project_lib::aquery]  CrateSpec {crate_id: "ID-external/....." }

This lead me to the following code which suggests that any leftover outputs from other configurations might impact generating rust-project.json and lead to the failure above

The "solution" was to run bazel clean and retry generating rust-project.json. This solution is not acceptable to me and should be considered a big. The tool should behave consistently even if there's some leftover files in bazel-out/.

I don't yet have a consistent repro but hoping someone else does 😅. Either way, thought this info would be useful.