Drop tracking ignores borrows with projections · Issue #93648 · rust-lang/rust (original) (raw)
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Description
For example:
fn main() { let _ = async { let mut s = (String::new(),); s.0.push_str("abc"); std::mem::drop(s); async {}.await; }; }
$ rustc +nightly-2022-01-22 --edition=2021 b.rs error: internal compiler error: compiler/rustc_mir_transform/src/generator.rs:755:13: Broken MIR: generator contains type (String,) in MIR, but typeck only knows about {ResumeTy, impl Future<Output = [async output]>, ()} and []
The TryFrom<&PlaceWithHirId<'_>> for TrackedValue fails for places with projections, so in that case borrow is never recorded:
| impl TryFrom<&PlaceWithHirId<'_>> for TrackedValue { |
|---|
| type Error = TrackedValueConversionError; |
| fn try_from(place_with_id: &PlaceWithHirId<'_>) -> Result<Self, Self::Error> { |
| if !place_with_id.place.projections.is_empty() { |
| debug!( |
| "TrackedValue from PlaceWithHirId: {:?} has projections, which are not supported.", |
| place_with_id |
| ); |
| return Err(TrackedValueConversionError::PlaceProjectionsNotSupported); |
| } |
| fn borrow( |
|---|
| &mut self, |
| place_with_id: &expr_use_visitor::PlaceWithHirId<'tcx>, |
| _diag_expr_id: HirId, |
| _bk: rustc_middle::ty::BorrowKind, |
| ) { |
| place_with_id |
| .try_into() |
| .map_or(false, |tracked_value |
| } |