Hang and unbounded memory consumption on invalid `Cargo.toml`

[kpreid]

Problem

When parsing an erroneous Cargo.toml consisting solely of the character ")" (and other possible cases, but this is the minimal one), Cargo commands including cargo metadata and cargo clean will rapidly consume increasing amounts of memory until killed.

The original situation in which I encountered this bug was from git merge conflict markers.

Steps

mkdir oom
cd oom
echo ')' > Cargo.toml
cargo +nightly metadata
^C

Version

$ cargo +nightly version --verbose
cargo 1.90.0-nightly (9b296973b 2025-07-25)
release: 1.90.0-nightly
commit-hash: 9b296973b425ffb159e12cf3cd56580fd5c85382
commit-date: 2025-07-25
host: aarch64-apple-darwin
libgit2: 1.9.1 (sys:0.20.2 vendored)
libcurl: 8.7.1 (sys:0.4.82+curl-8.14.1 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 3.5.0 8 Apr 2025
os: Mac OS 15.5.0 [64-bit]

This happens on current (and somewhat older) nightly but not on current beta or stable 1.88.0.

@rustbot label +regression-from-stable-to-nightly

[hanna-kruppe]

Should be fixed by updating to a toml version that includes toml-rs/toml#1003

[epage]

Yes, we need to update toml and toml_edit to pick up this fix and some loss of comments in cargo add. Since these seemed unlikely to hit, I was originally waiting closer to the beta branch in case others crop up but we can also do it now.

[weihanglo]

Just opened #15779, as beta cutoff will happen soon later this week.