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__arg variables from async fn desugaring are accessible to the user #60438
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A-async-await
Area: Async & Await
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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nikomatsakis
added
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
A-async-await
Area: Async & Await
labels
May 1, 2019
A complete test case: // aux-build:arc_wake.rs
// edition:2018
#![allow(unused_variables)]
#![feature(async_await, await_macro)]
extern crate arc_wake;
use arc_wake::ArcWake;
use std::future::Future;
use std::sync::Arc;
use std::task::Context;
struct EmptyWaker;
impl ArcWake for EmptyWaker {
fn wake(self: Arc<Self>) {}
}
async fn foobar_async(x: u32, (a, _, _c): (u32, u32, u32), _: u32, _y: u32) {
assert_eq!(__arg1, (1, 2, 3)); // this doesn't compile error, but should
assert_eq!(__arg2, 4);
}
fn main() {
let empty = Arc::new(EmptyWaker);
let waker = ArcWake::into_waker(empty);
let mut cx = Context::from_waker(&waker);
let mut fut = Box::pin(foobar_async(0, (1, 2, 3), 4, 0));
let _ = fut.as_mut().poll(&mut cx);
} |
Centril
added a commit
to Centril/rust
that referenced
this issue
May 1, 2019
Ensure that drop order of `async fn` matches `fn` and that users cannot refer to generated arguments. Fixes rust-lang#60236 and fixes rust-lang#60438. This PR modifies the lowering of `async fn` arguments so that the drop order matches the equivalent `fn`. Previously, async function arguments were lowered as shown below: async fn foo(<pattern>: <ty>) { async move { } } // <-- dropped as you "exit" the fn // ...becomes... fn foo(__arg0: <ty>) { async move { let <pattern> = __arg0; } // <-- dropped as you "exit" the async block } After this PR, async function arguments will be lowered as: async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) { async move { } } // <-- dropped as you "exit" the fn // ...becomes... fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) { async move { let __arg2 = __arg2; let <pattern> = __arg2; let __arg1 = __arg1; let <pattern> = __arg1; let __arg0 = __arg0; let <pattern> = __arg0; } // <-- dropped as you "exit" the async block } If `<pattern>` is a simple ident, then it is lowered to a single `let <pattern> = <pattern>;` statement as an optimization. This PR also stops users from referring to the generated `__argN` identifiers. r? @nikomatsakis
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Labels
A-async-await
Area: Async & Await
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
The fixes for #54716 and #60236 introduced
__arg
variables that, presently, are accessible to the user (playground):This code compiles, but it should error.
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