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Unhelpful error message when awaiting an async closure while forgetting the brackets #65923

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gilescope opened this issue Oct 29, 2019 · 0 comments · Fixed by #66239
Closed

Unhelpful error message when awaiting an async closure while forgetting the brackets #65923

gilescope opened this issue Oct 29, 2019 · 0 comments · Fixed by #66239
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A-async-await Area: Async & Await A-diagnostics Area: Messages for errors, warnings, and lints AsyncAwait-Triaged Async-await issues that have been triaged during a working group meeting. F-async_closure `#![feature(async_closure)]` P-low Low priority requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@gilescope
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async fn _async_bar() -> u32 {
    let async_closure = async || {
       22_u32
    };
    
    async_closure.await
}

(Playground link

Obviously async_closure().await was what I should have written. It would be great if rustc suggested that maybe I shoudl try calling the closure rather than the error it currently offers:

error[E0277]: the trait bound `[closure@src/main.rs:6:25: 8:6]: std::future::Future` is not satisfied
   --> src/main.rs:10:5
    |
10  |     async_closure.await
    |     ^^^^^^^^^^^^^^^^^^^ the trait `std::future::Future` is not implemented for `[closure@src/main.rs:6:25: 8:6]`
@Centril Centril added A-async-await Area: Async & Await AsyncAwait-Triaged Async-await issues that have been triaged during a working group meeting. F-async_closure `#![feature(async_closure)]` P-low Low priority requires-nightly This issue requires a nightly compiler in some way. A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 29, 2019
@estebank estebank mentioned this issue Nov 9, 2019
Merged
JohnTitor added a commit to JohnTitor/rust that referenced this issue Nov 19, 2019
@JohnTitor
Rollup merge of rust-lang#66239 - estebank:suggest-async-closure-call…
76a1e2c 
…, r=Centril

Suggest calling async closure when needed

When using an async closure as a value in a place that expects a future,
suggest calling the closure.

Fix rust-lang#65923.
Centril added a commit to Centril/rust that referenced this issue Nov 19, 2019
@Centril
Rollup merge of rust-lang#66239 - estebank:suggest-async-closure-call…
0b0d683 
…, r=Centril

Suggest calling async closure when needed

When using an async closure as a value in a place that expects a future,
suggest calling the closure.

Fix rust-lang#65923.
@bors bors closed this as completed in 0487f0c Nov 19, 2019
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A-async-await Area: Async & Await A-diagnostics Area: Messages for errors, warnings, and lints AsyncAwait-Triaged Async-await issues that have been triaged during a working group meeting. F-async_closure `#![feature(async_closure)]` P-low Low priority requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Suggest calling async closure when needed estebank/rust
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@gilescope @Centril