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Consider mutations as borrows in drop tracking
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This is needed to match MIR more conservative approximation of any
borrowed value being live across a suspend point (See rust-lang#94067). This
change considers an expression such as `x.y = z` to be a borrow of `x`
and therefore keeps `x` live across suspend points.
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eholk committed Feb 16, 2022
1 parent f90b06d commit 074d757
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Showing 4 changed files with 123 additions and 3 deletions.
Original file line number Diff line number Diff line change
Expand Up @@ -93,19 +93,25 @@ impl<'tcx> expr_use_visitor::Delegate<'tcx> for ExprUseDelegate<'tcx> {
fn borrow(
&mut self,
place_with_id: &expr_use_visitor::PlaceWithHirId<'tcx>,
_diag_expr_id: HirId,
diag_expr_id: HirId,
_bk: rustc_middle::ty::BorrowKind,
) {
debug!("borrow {:?}; diag_expr_id={:?}", place_with_id, diag_expr_id);
self.places
.borrowed
.insert(TrackedValue::from_place_with_projections_allowed(place_with_id));
}

fn mutate(
&mut self,
_assignee_place: &expr_use_visitor::PlaceWithHirId<'tcx>,
_diag_expr_id: HirId,
assignee_place: &expr_use_visitor::PlaceWithHirId<'tcx>,
diag_expr_id: HirId,
) {
debug!("mutate {:?}; diag_expr_id={:?}", assignee_place, diag_expr_id);
// Count mutations as a borrow.
self.places
.borrowed
.insert(TrackedValue::from_place_with_projections_allowed(assignee_place));
}

fn fake_read(
Expand Down
45 changes: 45 additions & 0 deletions src/test/ui/async-await/drop-track-field-assign-nonsend.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
// Derived from an ICE found in tokio-xmpp during a crater run.
// edition:2021
// compile-flags: -Zdrop-tracking

#![allow(dead_code)]

#[derive(Clone)]
struct InfoResult {
node: Option<std::rc::Rc<String>>
}

struct Agent {
info_result: InfoResult
}

impl Agent {
async fn handle(&mut self) {
let mut info = self.info_result.clone();
info.node = None;
let element = parse_info(info);
let _ = send_element(element).await;
}
}

struct Element {
}

async fn send_element(_: Element) {}

fn parse(_: &[u8]) -> Result<(), ()> {
Ok(())
}

fn parse_info(_: InfoResult) -> Element {
Element { }
}

fn assert_send<T: Send>(_: T) {}

fn main() {
let agent = Agent { info_result: InfoResult { node: None } };
// FIXME: It would be nice for this to work. See #94067.
assert_send(agent.handle());
//~^ cannot be sent between threads safely
}
25 changes: 25 additions & 0 deletions src/test/ui/async-await/drop-track-field-assign-nonsend.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
error: future cannot be sent between threads safely
--> $DIR/drop-track-field-assign-nonsend.rs:43:17
|
LL | assert_send(agent.handle());
| ^^^^^^^^^^^^^^ future returned by `handle` is not `Send`
|
= help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `Rc<String>`
note: future is not `Send` as this value is used across an await
--> $DIR/drop-track-field-assign-nonsend.rs:21:38
|
LL | let mut info = self.info_result.clone();
| -------- has type `InfoResult` which is not `Send`
...
LL | let _ = send_element(element).await;
| ^^^^^^ await occurs here, with `mut info` maybe used later
LL | }
| - `mut info` is later dropped here
note: required by a bound in `assert_send`
--> $DIR/drop-track-field-assign-nonsend.rs:38:19
|
LL | fn assert_send<T: Send>(_: T) {}
| ^^^^ required by this bound in `assert_send`

error: aborting due to previous error

44 changes: 44 additions & 0 deletions src/test/ui/async-await/drop-track-field-assign.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
// Derived from an ICE found in tokio-xmpp during a crater run.
// edition:2021
// compile-flags: -Zdrop-tracking
// build-pass

#![allow(dead_code)]

#[derive(Clone)]
struct InfoResult {
node: Option<String>
}

struct Agent {
info_result: InfoResult
}

impl Agent {
async fn handle(&mut self) {
let mut info = self.info_result.clone();
info.node = Some("bar".into());
let element = parse_info(info);
let _ = send_element(element).await;
}
}

struct Element {
}

async fn send_element(_: Element) {}

fn parse(_: &[u8]) -> Result<(), ()> {
Ok(())
}

fn parse_info(_: InfoResult) -> Element {
Element { }
}

fn main() {
let mut agent = Agent {
info_result: InfoResult { node: None }
};
let _ = agent.handle();
}

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