Panic with "already borrowed: BorrowMutError" since nightly-2024-03-26 about cargo HOT 5 CLOSED

I also observed this in https://github.com/dtolnay/rustversion/actions/runs/8429673336/job/23084341781, in which I use neither -Zminimal-versions nor -Zdirect-minimal-versions. Seems like a broader issue. Nightly-2024-03-26 is the first version affected in my case as well.

from cargo.

So it appears the reason manual testing and the test suite didn't hit this is there wasn't contention over the package lock. In fact, we only have one test that even attempts to capture the Blocking status.

We could try to make a specific test case to prevent regressions in this one case but then we'd likely run into this in other places. As an alternative, we could do a useless borrow of shell() further up the stack where it'd be unconditional so tests would be more likely to catch this.

from cargo.

Bisects to #13561 and specifically 4ab2797, using cargo test in the rustversion repo. @epage

from cargo.

From a quick look at the panic location (GlobalContext::shell), backtrace, and #13561 diff, it appears to be related to the fact that BorrowMut (returned by GlobalContext::shell), which previously persisted only during printing, now persists for the entire print_lockfile_updates.

from cargo.

we could do a useless borrow of shell() further up the stack where it'd be unconditional so tests would be more likely to catch this.

I wonder How it looks like and how it applies to other RefCell usages in the codebase.

from cargo.