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Auto merge of #64525 - nikomatsakis:issue-64512-drop-order-tail-temp,…
… r=davidtwco
adjust desugaring for async fn to correct drop order
Old desugaring, given a user function body `{ $stmts; $expr }`
```
{
let $param_pattern0 = $raw_param0;
...
let $param_patternN = $raw_paramN;
$stmts;
$expr
}
```
New desugaring:
```
{
let $param_pattern0 = $raw_param0;
...
let $param_patternN = $raw_paramN;
drop-temps {
$stmts;
$expr
}
}
```
The drop-temps is an internal bit of HIR that drops temporaries from the resulting expression, but it should be equivalent to `return { $stmts; $expr }`.
Fixes #64512
Fixes #64391- Loading branch information
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95 changes: 95 additions & 0 deletions
95
src/test/ui/async-await/drop-order/drop-order-for-temporary-in-tail-return-expr.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,95 @@ | ||
| // aux-build:arc_wake.rs | ||
| // edition:2018 | ||
| // run-pass | ||
|
|
||
| #![allow(unused_variables)] | ||
|
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||
| // Test the drop order for parameters relative to local variables and | ||
| // temporaries created in the tail return expression of the function | ||
| // body. In particular, check that this drop order is the same between | ||
| // a `async fn` and an ordinary `fn`. See #64512. | ||
|
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||
| extern crate arc_wake; | ||
|
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| use arc_wake::ArcWake; | ||
| use std::cell::RefCell; | ||
| use std::future::Future; | ||
| use std::sync::Arc; | ||
| use std::rc::Rc; | ||
| use std::task::Context; | ||
|
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| struct EmptyWaker; | ||
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| impl ArcWake for EmptyWaker { | ||
| fn wake(self: Arc<Self>) {} | ||
| } | ||
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| #[derive(Debug, Eq, PartialEq)] | ||
| enum DropOrder { | ||
| Function, | ||
| Val(&'static str), | ||
| } | ||
|
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| type DropOrderListPtr = Rc<RefCell<Vec<DropOrder>>>; | ||
|
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| struct D(&'static str, DropOrderListPtr); | ||
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| impl Drop for D { | ||
| fn drop(&mut self) { | ||
| self.1.borrow_mut().push(DropOrder::Val(self.0)); | ||
| } | ||
| } | ||
|
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||
| /// Check drop order of temporary "temp" as compared to `x`, `y`, and `z`. | ||
| /// | ||
| /// Expected order: | ||
| /// - `z` | ||
| /// - temp | ||
| /// - `y` | ||
| /// - `x` | ||
| async fn foo_async(x: D, _y: D) { | ||
| let l = x.1.clone(); | ||
| let z = D("z", l.clone()); | ||
| l.borrow_mut().push(DropOrder::Function); | ||
| helper_async(&D("temp", l)).await | ||
| } | ||
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| async fn helper_async(v: &D) { } | ||
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| fn foo_sync(x: D, _y: D) { | ||
| let l = x.1.clone(); | ||
| let z = D("z", l.clone()); | ||
| l.borrow_mut().push(DropOrder::Function); | ||
| helper_sync(&D("temp", l)) | ||
| } | ||
|
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| fn helper_sync(v: &D) { } | ||
|
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| fn assert_drop_order_after_poll<Fut: Future<Output = ()>>( | ||
| f: impl FnOnce(DropOrderListPtr) -> Fut, | ||
| g: impl FnOnce(DropOrderListPtr), | ||
| ) { | ||
| let empty = Arc::new(EmptyWaker); | ||
| let waker = ArcWake::into_waker(empty); | ||
| let mut cx = Context::from_waker(&waker); | ||
|
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||
| let actual_order = Rc::new(RefCell::new(Vec::new())); | ||
| let mut fut = Box::pin(f(actual_order.clone())); | ||
| let r = fut.as_mut().poll(&mut cx); | ||
|
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| assert!(match r { | ||
| std::task::Poll::Ready(()) => true, | ||
| _ => false, | ||
| }); | ||
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| let expected_order = Rc::new(RefCell::new(Vec::new())); | ||
| g(expected_order.clone()); | ||
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| assert_eq!(*actual_order.borrow(), *expected_order.borrow()); | ||
| } | ||
|
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| fn main() { | ||
| // Free functions (see doc comment on function for what it tests). | ||
| assert_drop_order_after_poll(|l| foo_async(D("x", l.clone()), D("_y", l.clone())), | ||
| |l| foo_sync(D("x", l.clone()), D("_y", l.clone()))); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,14 @@ | ||
| // Regression test for Issue #64391. The goal here is that this | ||
| // function compiles. In the past, due to incorrect drop order for | ||
| // temporaries in the tail expression, we failed to compile this | ||
| // example. The drop order itself is directly tested in | ||
| // `drop-order/drop-order-for-temporary-in-tail-return-expr.rs`. | ||
| // | ||
| // check-pass | ||
| // edition:2018 | ||
|
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| async fn add(x: u32, y: u32) -> u32 { | ||
| async { x + y }.await | ||
| } | ||
|
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| fn main() { } |