Rollup merge of #73672 - nellshamrell:async-fix, r=estebank
Adds a clearer message for when the async keyword is missing from a f… …unction This is a somewhat simple fix for #66731. Under the current version of Rust, if a user has a rust file that looks like this: ```rust fn boo (){} async fn foo() { boo().await; } fn main() { } ``` And they attempt to run it, they will receive an error message that looks like this: ```bash error: incorrect use of `await` --> test.rs:4:14 | 4 | boo.await(); | ^^ help: `await` is not a method call, remove the parentheses error[E0277]: the trait bound `fn() {boo}: std::future::Future` is not satisfied --> test.rs:4:5 | 4 | boo.await(); | ^^^^^^^^^ the trait `std::future::Future` is not implemented for `fn() {boo}` error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0277`. ``` This is not very clear. With the changes made in this PR, when a user compiles and runs that same rust code, they will receive an error message that looks like this: ```bash error[E0277]: `()` is not a future. --> test.rs:4:5 | 4 | boo().await; | ^^^^^^^^^^^ `()` is not a future | = help: the trait `std::future::Future` is not implemented for `()` = note: required by `std::future::Future::poll` ``` In the future, I think we should make this error message even clearer, perhaps through a solution like the one described in [this comment](https://github.com/rust-lang/rust/issues/66731#issuecomment-644394287). However, as that potentially involves a major change proposal, I would rather get this change in now and make the error message a little clearer while an MCP is drafted and discussed. Signed-off-by: Nell Shamrell <nellshamrell@gmail.com>
This commit is contained in:
Manish Goregaokar
GitHub
commit
d227a825bc
@ -27,6 +27,7 @@
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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#[stable(feature = "futures_api", since = "1.36.0")]
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#[lang = "future_trait"]
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#[rustc_on_unimplemented(label = "`{Self}` is not a future", message = "`{Self}` is not a future")]
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pub trait Future {
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/// The type of value produced on completion.
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#[stable(feature = "futures_api", since = "1.36.0")]
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@ -5,7 +5,7 @@
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use std::future::Future;
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fn get_future() -> impl Future<Output = ()> {
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//~^ ERROR the trait bound `(): std::future::Future` is not satisfied
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//~^ ERROR `()` is not a future
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panic!()
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}
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@ -1,12 +1,13 @@
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error[E0277]: the trait bound `(): std::future::Future` is not satisfied
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error[E0277]: `()` is not a future
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--> $DIR/async-error-span.rs:7:20
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LL | fn get_future() -> impl Future<Output = ()> {
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| ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::future::Future` is not implemented for `()`
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| ^^^^^^^^^^^^^^^^^^^^^^^^ `()` is not a future
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LL |
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LL | panic!()
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| -------- this returned value is of type `!`
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= help: the trait `std::future::Future` is not implemented for `()`
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= note: the return type of a function must have a statically known size
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error[E0698]: type inside `async fn` body must be known in this context
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@ -6,7 +6,7 @@ async fn fun() {
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//~| error: `.await` is not allowed in a `const`
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//~| error: `loop` is not allowed in a `const`
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//~| error: `.await` is not allowed in a `const`
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//~| error: the trait bound `(): std::future::Future` is not satisfied
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//~| error: `()` is not a future
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}
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fn main() {}
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@ -27,12 +27,13 @@ error[E0744]: `.await` is not allowed in a `const`
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LL | [1; ().await];
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| ^^^^^^^^
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error[E0277]: the trait bound `(): std::future::Future` is not satisfied
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error[E0277]: `()` is not a future
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--> $DIR/issue-70594.rs:4:9
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LL | [1; ().await];
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| ^^^^^^^^ the trait `std::future::Future` is not implemented for `()`
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| ^^^^^^^^ `()` is not a future
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= help: the trait `std::future::Future` is not implemented for `()`
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= note: required by `std::future::Future::poll`
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error: aborting due to 5 previous errors
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@ -27,12 +27,13 @@ LL | fn main() {
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LL | (|_| 2333).await;
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| ^^^^^^^^^^^^^^^^ only allowed inside `async` functions and blocks
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error[E0277]: the trait bound `[closure@$DIR/issue-62009-1.rs:12:5: 12:15]: std::future::Future` is not satisfied
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error[E0277]: `[closure@$DIR/issue-62009-1.rs:12:5: 12:15]` is not a future
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--> $DIR/issue-62009-1.rs:12:5
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LL | (|_| 2333).await;
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| ^^^^^^^^^^^^^^^^ the trait `std::future::Future` is not implemented for `[closure@$DIR/issue-62009-1.rs:12:5: 12:15]`
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| ^^^^^^^^^^^^^^^^ `[closure@$DIR/issue-62009-1.rs:12:5: 12:15]` is not a future
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= help: the trait `std::future::Future` is not implemented for `[closure@$DIR/issue-62009-1.rs:12:5: 12:15]`
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= note: required by `std::future::Future::poll`
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error: aborting due to 4 previous errors
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@ -1,5 +1,5 @@
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fn test_ref(x: &u32) -> impl std::future::Future<Output = u32> + '_ {
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*x //~^ ERROR the trait bound `u32: std::future::Future` is not satisfied
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*x //~^ ERROR `u32` is not a future
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}
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fn main() {
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@ -4,14 +4,15 @@ error[E0425]: cannot find value `u` in this scope
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LL | let _ = test_ref & u;
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| ^ not found in this scope
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error[E0277]: the trait bound `u32: std::future::Future` is not satisfied
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error[E0277]: `u32` is not a future
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--> $DIR/issues-71798.rs:1:25
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LL | fn test_ref(x: &u32) -> impl std::future::Future<Output = u32> + '_ {
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::future::Future` is not implemented for `u32`
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `u32` is not a future
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LL | *x
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| -- this returned value is of type `u32`
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= help: the trait `std::future::Future` is not implemented for `u32`
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= note: the return type of a function must have a statically known size
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error: aborting due to 2 previous errors
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@ -1,4 +1,4 @@
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error[E0277]: the trait bound `fn() -> impl std::future::Future {foo}: std::future::Future` is not satisfied
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error[E0277]: `fn() -> impl std::future::Future {foo}` is not a future
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:10:9
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LL | async fn foo() {}
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@ -8,14 +8,15 @@ LL | fn bar(f: impl Future<Output=()>) {}
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| ----------------- required by this bound in `bar`
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...
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LL | bar(foo);
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| ^^^ the trait `std::future::Future` is not implemented for `fn() -> impl std::future::Future {foo}`
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| ^^^ `fn() -> impl std::future::Future {foo}` is not a future
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= help: the trait `std::future::Future` is not implemented for `fn() -> impl std::future::Future {foo}`
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help: use parentheses to call the function
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LL | bar(foo());
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| ^^
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error[E0277]: the trait bound `[closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:11:25: 11:36]: std::future::Future` is not satisfied
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error[E0277]: `[closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:11:25: 11:36]` is not a future
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:12:9
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LL | fn bar(f: impl Future<Output=()>) {}
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@ -24,8 +25,9 @@ LL | fn bar(f: impl Future<Output=()>) {}
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LL | let async_closure = async || ();
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| -------- consider calling this closure
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LL | bar(async_closure);
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| ^^^^^^^^^^^^^ the trait `std::future::Future` is not implemented for `[closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:11:25: 11:36]`
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| ^^^^^^^^^^^^^ `[closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:11:25: 11:36]` is not a future
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= help: the trait `std::future::Future` is not implemented for `[closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:11:25: 11:36]`
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help: use parentheses to call the closure
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LL | bar(async_closure());
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