Panic with "already borrowed: BorrowMutError" since nightly-2024-03-26

[taiki-e]

Problem

Since nightly-2024-03-26, -Z minimal-versions and -Z direct-minimal-versions panic on some my projects when lockfile is already exists.

EDIT: this seems to be reproducible without -Z minimal-versions/-Z direct-minimal-versions: #13646 (comment)

Steps

$ git clone https://github.com/taiki-e/easytime
$ cd easytime
$ cargo generate-lockfile
$ cargo update -Z minimal-versions
    Updating crates.io index
 Downgrading aho-corasick v1.1.3 -> v0.6.0 (latest: v1.1.3)
 Downgrading anyhow v1.0.81 -> v1.0.0 (latest: v1.0.81)
thread 'main' panicked at src/cargo/util/context/mod.rs:412:20:
already borrowed: BorrowMutError
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::cell::panic_already_borrowed
   3: <cargo::util::progress::State>::tick
   4: <cargo::sources::registry::http_remote::HttpRegistry as cargo::sources::registry::RegistryData>::block_until_ready
   5: <cargo::sources::registry::RegistrySource as cargo::sources::source::Source>::block_until_ready
   6: <cargo::sources::replaced::ReplacedSource as cargo::sources::source::Source>::block_until_ready
   7: <cargo::core::registry::PackageRegistry as cargo::core::registry::Registry>::block_until_ready
   8: cargo::ops::cargo_generate_lockfile::print_lockfile_updates
   9: cargo::ops::cargo_generate_lockfile::update_lockfile
  10: cargo::commands::update::exec
  11: <cargo::cli::Exec>::exec
  12: cargo::cli::main
  13: cargo::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

It can be work around by removing Cargo.lock before calling -Z minimal-versions.

It can also be reproduced with https://github.com/taiki-e/pin-project-lite.

It can also be reproduced with -Z direct-minimal-versions.

$ cargo minimal-versions build --workspace --no-private --detach-path-deps=skip-exact --all-features --direct
info: running `cargo update -Z direct-minimal-versions`
thread 'main' panicked at src/cargo/util/context/mod.rs:412:20:
already borrowed: BorrowMutError

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.79.0-nightly (a510712d0 2024-03-25)
release: 1.79.0-nightly
commit-hash: a510712d05c6c98f987af24dd73cdfafee8922e6
commit-date: 2024-03-25
host: aarch64-apple-darwin
libgit2: 1.7.2 (sys:0.18.2 vendored)
libcurl: 8.4.0 (sys:0.4.72+curl-8.6.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Mac OS 14.4.0 [64-bit]

[dtolnay]

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.

[dtolnay]

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

[taiki-e]

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.