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Auto merge of rust-lang#64525 - nikomatsakis:issue-64512-drop-order-t…
…ail-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 rust-lang#64512 Fixes rust-lang#64391
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src/test/ui/async-await/drop-order/drop-order-for-temporary-in-tail-return-expr.rs
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// aux-build:arc_wake.rs | ||
// edition:2018 | ||
// run-pass | ||
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#![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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// 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() { } |