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ignore boring locals when explaining borrow due to drop

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Polonius liveness has to contain boring locals, and we ignore them in
diagnostics to match NLL diagnostics, since they doesn't contain boring locals.

We ignored these when explaining why a loan contained a point due to
a use of a live var, but not when it contained a point due to a drop of
a live var.
This commit is contained in:
Rémy Rakic 2025-10-15 15:47:44 +00:00
parent 4f08307f6e
commit 68080de4e3
2 changed files with 6 additions and 4 deletions
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4
compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
View file

@ -687,7 +687,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
}
}
Some(Cause::DropVar(local, location)) => {
Some(Cause::DropVar(local, location)) if !is_local_boring(local) => {
let mut should_note_order = false;
if self.local_name(local).is_some()
&& let Some((WriteKind::StorageDeadOrDrop, place)) = kind_place
@ -705,7 +705,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
}
}
Some(Cause::LiveVar(..)) | None => {
Some(Cause::LiveVar(..) | Cause::DropVar(..)) | None => {
// Here, under NLL: no cause was found. Under polonius: no cause was found, or a
// boring local was found, which we ignore like NLLs do to match its diagnostics.
if let Some(region) = self.to_error_region_vid(borrow_region_vid) {

6
tests/ui/nll/polonius/lending-iterator-sanity-checks.polonius.stderr
View file

@ -1,13 +1,15 @@
error[E0499]: cannot borrow `*t` as mutable more than once at a time
--> $DIR/lending-iterator-sanity-checks.rs:19:19
|
LL | fn use_live<T: LendingIterator>(t: &mut T) -> Option<(T::Item<'_>, T::Item<'_>)> {
| - let's call the lifetime of this reference `'1`
LL | let Some(i) = t.next() else { return None };
| - first mutable borrow occurs here
LL | let Some(j) = t.next() else { return None };
| ^ second mutable borrow occurs here
...
LL | }
| - first borrow might be used here, when `i` is dropped and runs the destructor for type `<T as LendingIterator>::Item<'_>`
LL | Some((i, j))
| ------------ returning this value requires that `*t` is borrowed for `'1`
error[E0499]: cannot borrow `*t` as mutable more than once at a time
--> $DIR/lending-iterator-sanity-checks.rs:31:13