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Unsound two-phase borrow accepted by compiler #164163
Description
The following code compiles:
pub fn main() {
let mut a: Vec<u64> = vec![1];
let mut b: Vec<u64> = vec![2];
let mut p: &mut Vec<u64> = &mut a;
let s: &u64;
// The receiver `&mut *p` is reserved first. The argument then borrows through `p`, and points `p` elsewhere.
p.push({
s = &p[0];
p = &mut b;
0
});
// `a` has been pushed to, so it may have reallocated. `s` still points into its old buffer.
for _ in 0..64 { p.push(7); }
println!("{}", *s);
}I expected to see this happen: compilation fails
Instead, this happened: prints random garbage when run
Meta
Happens on nightly, stable, and past stables at least back to 1.85.0 on godbolt:
Activity
theemathas commentedon Oct 11, 2026
Is this a duplicate of #160598?
jsnell commentedon Oct 11, 2026
I wouldn't think so. That bug seems to be about control-flow, which is trivial here, and the actual trigger is re-assignment.
zachs18 commentedon Oct 11, 2026
2015 edition bisection
searched toolchains nightly-2018-12-04 through nightly-2022-05-14
Regression in nightly-2019-04-23
fetching https://static.rust-lang.org/dist/2019-04-22/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2019-04-22: 40 B / 40 B [===================================================================================================================] 100.00 % 960.03 KB/s converted 2019-04-22 to 31a75a1
fetching https://static.rust-lang.org/dist/2019-04-23/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2019-04-23: 40 B / 40 B [=====================================================================================================================] 100.00 % 1.12 MB/s converted 2019-04-23 to 6d59933
looking for regression commit between 2019-04-22 and 2019-04-23
fetching (via remote github) commits from max(31a75a1, 2019-04-20) to 6d59933
ending github query because we found starting sha: 31a75a1
get_commits_between returning commits, len: 6
commit[0] 2019-04-21: Auto merge of #60124 - petrochenkov:stanomut, r=eddyb
commit[1] 2019-04-21: Auto merge of #60158 - Xanewok:update-clippy, r=matthiaskrgr
commit[2] 2019-04-22: Auto merge of #60053 - Xanewok:serde-save-analysis, r=nrc
commit[3] 2019-04-22: Auto merge of #60133 - phansch:deny_rust_2018_idioms, r=Centril
commit[4] 2019-04-22: Auto merge of #59114 - matthewjasper:enable-migate-2015, r=pnkfelix
commit[5] 2019-04-22: Auto merge of #60168 - varkor:tidy-leading-newline, r=alexcrichton
ERROR: no CI builds available between 31a75a1 and 6d59933 within last 167 days
bisected with
cargo-bisect-rustccargo bisect-rustc --preserve --start 1.32.0 --end 1.62.0 --regress successon edition 20152018 edition (stable) bisection
searched toolchains nightly-2018-06-20 through nightly-2018-12-04Regression in nightly-2018-09-10
fetching https://static.rust-lang.org/dist/2018-09-09/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2018-09-09: 40 B / 40 B [=====================================================================================================================] 100.00 % 1.08 MB/s converted 2018-09-09 to 0198a1e
fetching https://static.rust-lang.org/dist/2018-09-10/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2018-09-10: 40 B / 40 B [===================================================================================================================] 100.00 % 977.81 KB/s converted 2018-09-10 to 2d4e34c
looking for regression commit between 2018-09-09 and 2018-09-10
fetching (via remote github) commits from max(0198a1e, 2018-09-07) to 2d4e34c
ending github query because we found starting sha: 0198a1e
get_commits_between returning commits, len: 8
commit[0] 2018-09-08: Auto merge of #53909 - mikhail-m1:53643, r=nikomatsakis
commit[1] 2018-09-09: Auto merge of #53949 - estebank:unclosed-delim, r=nikomatsakis
commit[2] 2018-09-09: Auto merge of #53960 - estebank:issue-51303, r=nagisa
commit[3] 2018-09-09: Auto merge of #53988 - eddyb:issue-53770, r=petrochenkov
commit[4] 2018-09-09: Auto merge of #53998 - eddyb:issue-53728, r=oli-obk
commit[5] 2018-09-09: Auto merge of #53902 - dtolnay:group, r=petrochenkov
commit[6] 2018-09-09: Auto merge of #54057 - matthiaskrgr:stabilize-edition-plus-clippy, r=Mark-Simulacrum
commit[7] 2018-09-09: Auto merge of #53778 - petrochenkov:shadrelax2, r=nikomatsakis
ERROR: no CI builds available between 0198a1e and 2d4e34c within last 167 days
bisected with
cargo-bisect-rustccargo bisect-rustc --preserve --end 1.32.0 --start 2018-06-20 --regress successon edition 2018. This includes the stabilization of the 2018 edition.2018 edition (unstable) bisection
With `cargo-features = ["edition"]`:searched toolchains nightly-2018-06-20 through nightly-2018-12-04
Regression in nightly-2018-08-03
fetching https://static.rust-lang.org/dist/2018-08-02/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2018-08-02: 40 B / 40 B [=====================================================================================================================] 100.00 % 1.56 MB/s converted 2018-08-02 to 97085f9
fetching https://static.rust-lang.org/dist/2018-08-03/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2018-08-03: 40 B / 40 B [=====================================================================================================================] 100.00 % 1.37 MB/s converted 2018-08-03 to 7e8ca9f
looking for regression commit between 2018-08-02 and 2018-08-03
fetching (via remote github) commits from max(97085f9, 2018-07-31) to 7e8ca9f
ending github query because we found starting sha: 97085f9
get_commits_between returning commits, len: 12
commit[0] 2018-08-01: Auto merge of #52958 - pietroalbini:rollup, r=pietroalbini
commit[1] 2018-08-02: Auto merge of #52206 - RalfJung:zst-slices, r=alexcrichton
commit[2] 2018-08-02: Auto merge of #52787 - riscv-rust:riscv-rust-pr, r=alexcrichton
commit[3] 2018-08-02: Auto merge of #52847 - upsuper:thread-stack-reserve, r=alexcrichton
commit[4] 2018-08-02: Auto merge of #52890 - djrenren:test-visibility, r=petrochenkov
commit[5] 2018-08-02: Auto merge of #52906 - RalfJung:jemalloc, r=alexcrichton
commit[6] 2018-08-02: Auto merge of #52975 - pnkfelix:issue-52967-edition-2018-implies-2-phase-borrows, r=Mark-Simulacrum
commit[7] 2018-08-02: Auto merge of #52949 - Mark-Simulacrum:snap, r=alexcrichton
commit[8] 2018-08-02: Auto merge of #52782 - pnkfelix:issue-45696-dangly-paths-for-box, r=eddyb
commit[9] 2018-08-02: Auto merge of #52841 - petrochenkov:premacro, r=alexcrichton
commit[10] 2018-08-03: Auto merge of #51657 - wesleywiser:wip_profiling, r=eddyb
commit[11] 2018-08-03: Auto merge of #52919 - alexcrichton:update-cargo, r=Mark-Simulacrum
ERROR: no CI builds available between 97085f9 and 7e8ca9f within last 167 days
bisected with
cargo-bisect-rustccargo bisect-rustc --preserve --end 1.32.0 --start 2018-06-20 --regress successon edition 2018 withcargo-features = ["edition"]. This includes #52975pnkfelix:issue-52967-edition-2018-implies-2-phase-borrowsOn the 2015 edition bisection, #59114
enable-migate-2015seems related, this issue is present in the first stable 2018 edition nightly, and on the unstable 2018 edition bisection, #52975pnkfelix:issue-52967-edition-2018-implies-2-phase-borrowsseems related, so this seems like an issue that has existed in two-phase borrows/NLL(?) since it was introduced.rustbot commentedon Oct 14, 2026
Assigning P-high (discussion on Zulip).