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Auto merge of #105094 - Swatinem:generator-not-future, r=compiler-errors
Make sure async constructs do not `impl Generator` Async lowering turns async functions and blocks into generators internally. Though these special kinds of generators should not `impl Generator` themselves. The other way around, normal generators should not `impl Future`. This was discovered in #105082 (comment) and is a regression from #104321. r? `@compiler-errors`
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,45 @@ | ||
// edition:2018 | ||
#![feature(generators, generator_trait)] | ||
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use std::future::Future; | ||
use std::ops::Generator; | ||
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async fn async_fn() {} | ||
fn returns_async_block() -> impl Future<Output = ()> { | ||
async {} | ||
} | ||
fn returns_generator() -> impl Generator<(), Yield = (), Return = ()> { | ||
|| { | ||
let _: () = yield (); | ||
} | ||
} | ||
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fn takes_future(_f: impl Future<Output = ()>) {} | ||
fn takes_generator<ResumeTy>(_g: impl Generator<ResumeTy, Yield = (), Return = ()>) {} | ||
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fn main() { | ||
// okay: | ||
takes_future(async_fn()); | ||
takes_future(returns_async_block()); | ||
takes_future(async {}); | ||
takes_generator(returns_generator()); | ||
takes_generator(|| { | ||
let _: () = yield (); | ||
}); | ||
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// async futures are not generators: | ||
takes_generator(async_fn()); | ||
//~^ ERROR the trait bound | ||
takes_generator(returns_async_block()); | ||
//~^ ERROR the trait bound | ||
takes_generator(async {}); | ||
//~^ ERROR the trait bound | ||
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// generators are not futures: | ||
takes_future(returns_generator()); | ||
//~^ ERROR is not a future | ||
takes_future(|ctx| { | ||
//~^ ERROR is not a future | ||
ctx = yield (); | ||
}); | ||
} |
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error[E0277]: the trait bound `impl Future<Output = ()>: Generator<_>` is not satisfied | ||
--> $DIR/generator-not-future.rs:31:21 | ||
| | ||
LL | takes_generator(async_fn()); | ||
| --------------- ^^^^^^^^^^ the trait `Generator<_>` is not implemented for `impl Future<Output = ()>` | ||
| | | ||
| required by a bound introduced by this call | ||
| | ||
note: required by a bound in `takes_generator` | ||
--> $DIR/generator-not-future.rs:18:39 | ||
| | ||
LL | fn takes_generator<ResumeTy>(_g: impl Generator<ResumeTy, Yield = (), Return = ()>) {} | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `takes_generator` | ||
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error[E0277]: the trait bound `impl Future<Output = ()>: Generator<_>` is not satisfied | ||
--> $DIR/generator-not-future.rs:33:21 | ||
| | ||
LL | takes_generator(returns_async_block()); | ||
| --------------- ^^^^^^^^^^^^^^^^^^^^^ the trait `Generator<_>` is not implemented for `impl Future<Output = ()>` | ||
| | | ||
| required by a bound introduced by this call | ||
| | ||
note: required by a bound in `takes_generator` | ||
--> $DIR/generator-not-future.rs:18:39 | ||
| | ||
LL | fn takes_generator<ResumeTy>(_g: impl Generator<ResumeTy, Yield = (), Return = ()>) {} | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `takes_generator` | ||
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error[E0277]: the trait bound `[async block@$DIR/generator-not-future.rs:35:21: 35:29]: Generator<_>` is not satisfied | ||
--> $DIR/generator-not-future.rs:35:21 | ||
| | ||
LL | takes_generator(async {}); | ||
| --------------- ^^^^^^^^ the trait `Generator<_>` is not implemented for `[async block@$DIR/generator-not-future.rs:35:21: 35:29]` | ||
| | | ||
| required by a bound introduced by this call | ||
| | ||
note: required by a bound in `takes_generator` | ||
--> $DIR/generator-not-future.rs:18:39 | ||
| | ||
LL | fn takes_generator<ResumeTy>(_g: impl Generator<ResumeTy, Yield = (), Return = ()>) {} | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `takes_generator` | ||
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error[E0277]: `impl Generator<Yield = (), Return = ()>` is not a future | ||
--> $DIR/generator-not-future.rs:39:18 | ||
| | ||
LL | takes_future(returns_generator()); | ||
| ------------ ^^^^^^^^^^^^^^^^^^^ `impl Generator<Yield = (), Return = ()>` is not a future | ||
| | | ||
| required by a bound introduced by this call | ||
| | ||
= help: the trait `Future` is not implemented for `impl Generator<Yield = (), Return = ()>` | ||
= note: impl Generator<Yield = (), Return = ()> must be a future or must implement `IntoFuture` to be awaited | ||
note: required by a bound in `takes_future` | ||
--> $DIR/generator-not-future.rs:17:26 | ||
| | ||
LL | fn takes_future(_f: impl Future<Output = ()>) {} | ||
| ^^^^^^^^^^^^^^^^^^^ required by this bound in `takes_future` | ||
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error[E0277]: `[generator@$DIR/generator-not-future.rs:41:18: 41:23]` is not a future | ||
--> $DIR/generator-not-future.rs:41:18 | ||
| | ||
LL | takes_future(|ctx| { | ||
| _____------------_^ | ||
| | | | ||
| | required by a bound introduced by this call | ||
LL | | | ||
LL | | ctx = yield (); | ||
LL | | }); | ||
| |_____^ `[generator@$DIR/generator-not-future.rs:41:18: 41:23]` is not a future | ||
| | ||
= help: the trait `Future` is not implemented for `[generator@$DIR/generator-not-future.rs:41:18: 41:23]` | ||
= note: [generator@$DIR/generator-not-future.rs:41:18: 41:23] must be a future or must implement `IntoFuture` to be awaited | ||
note: required by a bound in `takes_future` | ||
--> $DIR/generator-not-future.rs:17:26 | ||
| | ||
LL | fn takes_future(_f: impl Future<Output = ()>) {} | ||
| ^^^^^^^^^^^^^^^^^^^ required by this bound in `takes_future` | ||
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error: aborting due to 5 previous errors | ||
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For more information about this error, try `rustc --explain E0277`. |