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VecDeque::iter_mut tramples on the references it returned earlier #74029
Description
I tried running this code with Miri (on playground):
fn test_all_refs<'a, T: 'a>(dummy: &mut T, iter: impl Iterator<Item = &'a mut T>) {
// Gather all those references.
let mut refs: Vec<&mut T> = iter.collect();
// Use them all. Twice, to be sure we got all interleavings.
for r in refs.iter_mut() {
std::mem::swap(dummy, r);
}
for r in refs {
std::mem::swap(dummy, r);
}
}
fn main() {
let mut v = std::collections::VecDeque::new();
v.push_back(1);
v.push_back(2);
test_all_refs(&mut 0, v.iter_mut());
}I expected to see it end gracefully.
Instead, it reports:
error: Undefined Behavior: trying to reborrow for Unique, but parent tag <4482> does not have an appropriate item in the borrow stack
--> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc/vec.rs:2099:53
|
2099 | ptr::write(vector.as_mut_ptr(), element);
| ^^^^^^^ trying to reborrow for Unique, but parent tag <4482> does not have an appropriate item in the borrow stack
|
= help: this indicates a potential bug in the program: it performed an invalid operation, but the rules it violated are still experimental
= help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
= note: inside `<std::vec::Vec<&mut i32> as std::vec::SpecExtend<&mut i32, std::collections::vec_deque::IterMut<i32>>>::from_iter` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc/vec.rs:2099:53
= note: inside `<std::vec::Vec<&mut i32> as std::iter::FromIterator<&mut i32>>::from_iter::<std::collections::vec_deque::IterMut<i32>>` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc/vec.rs:1995:9
= note: inside `<std::collections::vec_deque::IterMut<i32> as std::iter::Iterator>::collect::<std::vec::Vec<&mut i32>>` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/iter/traits/iterator.rs:1671:9
note: inside `test_all_refs::<i32, std::collections::vec_deque::IterMut<i32>>` at src/main.rs:3:33
--> src/main.rs:3:33
|
3 | let mut refs: Vec<&mut T> = iter.collect();
| ^^^^^^^^^^^^^^
note: inside `main` at src/main.rs:17:5
--> src/main.rs:17:5
|
17 | test_all_refs(&mut 0, v.iter_mut());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: inside closure at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:67:34
= note: inside closure at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:52:73
= note: inside `std::sys_common::backtrace::__rust_begin_short_backtrace::<[closure@std::rt::lang_start_internal::{{closure}}#0::{{closure}}#0 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/sys_common/backtrace.rs:130:5
= note: inside closure at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:52:13
= note: inside `std::panicking::r#try::do_call::<[closure@std::rt::lang_start_internal::{{closure}}#0 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panicking.rs:342:40
= note: inside `std::panicking::r#try::<i32, [closure@std::rt::lang_start_internal::{{closure}}#0 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe]>` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panicking.rs:319:15
= note: inside `std::panic::catch_unwind::<[closure@std::rt::lang_start_internal::{{closure}}#0 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panic.rs:394:14
= note: inside `std::rt::lang_start_internal` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:51:25
= note: inside `std::rt::lang_start::<()>` at /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:67:5
Activity
leonardo-m commentedon Jul 4, 2020
The code of VecDeque seems the right one to functionally verify with something from this list:
https://alastairreid.github.io/rust-verification-tools/
ssomers commentedon Jul 14, 2020
Let's also add a test for this case of undefined behaviour exposed by Miri.
RalfJung commentedon Sep 19, 2020
Proposed fix is up at #76911
Rollup merge of rust-lang#76911 - RalfJung:vecdeque-aliasing, r=oli-obk