Constant "cargo check" invalidation

I searched around a lot, and there are other people reporting similar issues, but I think this stands alone because I've ruled out all the other mentioned issues AFAIK.

In short: every time I save, including after very minor changes, cargo check runs (expected) and checks all dependencies (unexpected) taking several minutes. To my knowledge this didn't always happen.

I run 1 instance of VS code, and I set

  "rust-analyzer.cargo.extraEnv": {
    "CARGO_TARGET_DIR": "/mnt/scratch/ra_cargo_target"
  },
  "rust-analyzer.check.extraEnv": {
    "CARGO_TARGET_DIR": "/mnt/scratch/ra_cargo_target"
  }

which is used only by rust-analyzer. I don't run cargo, or any other external processes on rust code. This happens when I make a change, save, then change the line very slight, and save again (i.e. at most a few seconds between invocations).

Here's a list of things people have suggested:

• Different RUSTFLAGS (nothing in my env var, but every run should be consistent since it's all a single RA process)
• Different pkgconfig env vars (single RA process, same as above)
• Background process invalidating things (not running cargo watch or other vs code instances)
• Sharing a cache with a different target (AFAIK cargo writes to different dirs for different targets, but again this is all a single RA process so unless it's invalidating itself I don't see how it could be invalidated)

FWIW the vs code workspace does have mixed targets - x86 and wasm, with one local package shared between them.

Start by reproducing the repeated cargo check behavior through the rust-analyzer VS Code settings, using the shared x86 and wasm workspace and CARGO_TARGET_DIR. Trace the cargo/check invalidation path and verify that consecutive minor saves no longer rebuild unchanged dependencies.