Prefer AsyncFn* over Fn* for coroutine-closures

3 files changed, 30 insertions, 9 deletions

diff --git a/tests/ui/async-await/async-closures/is-not-fn.rs b/tests/ui/async-await/async-closures/is-not-fn.rs
index 94c8e8563bd..40b0febbf06 100644
--- a/tests/ui/async-await/async-closures/is-not-fn.rs
+++ b/tests/ui/async-await/async-closures/is-not-fn.rs
@@ -5,8 +5,5 @@
 fn main() {
     fn needs_fn(x: impl FnOnce()) {}
     needs_fn(async || {});
-    //~^ ERROR expected a `FnOnce()` closure, found `{coroutine-closure@
-    // FIXME(async_closures): This should explain in more detail how async fns don't
-    // implement the regular `Fn` traits. Or maybe we should just fix it and make them
-    // when there are no upvars or whatever.
+    //~^ ERROR expected `{coroutine-closure@is-not-fn.rs:7:14}` to be a closure that returns `()`
 }
diff --git a/tests/ui/async-await/async-closures/is-not-fn.stderr b/tests/ui/async-await/async-closures/is-not-fn.stderr
index 12da4b1fc6f..6169cee85fd 100644
--- a/tests/ui/async-await/async-closures/is-not-fn.stderr
+++ b/tests/ui/async-await/async-closures/is-not-fn.stderr
@@ -1,13 +1,13 @@
-error[E0277]: expected a `FnOnce()` closure, found `{coroutine-closure@$DIR/is-not-fn.rs:7:14: 7:22}`
+error[E0271]: expected `{coroutine-closure@is-not-fn.rs:7:14}` to be a closure that returns `()`, but it returns `{async closure body@$DIR/is-not-fn.rs:7:23: 7:25}`
   --> $DIR/is-not-fn.rs:7:14
    |
 LL |     needs_fn(async || {});
-   |     -------- ^^^^^^^^^^^ expected an `FnOnce()` closure, found `{coroutine-closure@$DIR/is-not-fn.rs:7:14: 7:22}`
+   |     -------- ^^^^^^^^^^^ expected `()`, found `async` closure body
    |     |
    |     required by a bound introduced by this call
    |
-   = help: the trait `FnOnce<()>` is not implemented for `{coroutine-closure@$DIR/is-not-fn.rs:7:14: 7:22}`
-   = note: wrap the `{coroutine-closure@$DIR/is-not-fn.rs:7:14: 7:22}` in a closure with no arguments: `|| { /* code */ }`
+   = note:         expected unit type `()`
+           found `async` closure body `{async closure body@$DIR/is-not-fn.rs:7:23: 7:25}`
 note: required by a bound in `needs_fn`
   --> $DIR/is-not-fn.rs:6:25
    |
@@ -16,4 +16,4 @@ LL |     fn needs_fn(x: impl FnOnce()) {}
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0271`.
diff --git a/tests/ui/async-await/async-fn/dyn-pos.stderr b/tests/ui/async-await/async-fn/dyn-pos.stderr
index c9323526516..488c5d06938 100644
--- a/tests/ui/async-await/async-fn/dyn-pos.stderr
+++ b/tests/ui/async-await/async-fn/dyn-pos.stderr
@@ -8,6 +8,9 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
   --> $SRC_DIR/core/src/ops/async_function.rs:LL:COL
    |
    = note: the trait cannot be made into an object because it contains the generic associated type `CallFuture`
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFn` for this new enum and using it instead:
+             &F
+             std::boxed::Box<F, A>
 
 error[E0038]: the trait `AsyncFnMut` cannot be made into an object
   --> $DIR/dyn-pos.rs:5:16
@@ -19,6 +22,10 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
   --> $SRC_DIR/core/src/ops/async_function.rs:LL:COL
    |
    = note: the trait cannot be made into an object because it contains the generic associated type `CallMutFuture`
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFnMut` for this new enum and using it instead:
+             &F
+             &mut F
+             std::boxed::Box<F, A>
 
 error[E0038]: the trait `AsyncFn` cannot be made into an object
   --> $DIR/dyn-pos.rs:5:16
@@ -30,6 +37,9 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
   --> $SRC_DIR/core/src/ops/async_function.rs:LL:COL
    |
    = note: the trait cannot be made into an object because it contains the generic associated type `CallFuture`
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFn` for this new enum and using it instead:
+             &F
+             std::boxed::Box<F, A>
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0038]: the trait `AsyncFnMut` cannot be made into an object
@@ -42,6 +52,10 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
   --> $SRC_DIR/core/src/ops/async_function.rs:LL:COL
    |
    = note: the trait cannot be made into an object because it contains the generic associated type `CallMutFuture`
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFnMut` for this new enum and using it instead:
+             &F
+             &mut F
+             std::boxed::Box<F, A>
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0038]: the trait `AsyncFn` cannot be made into an object
@@ -54,6 +68,9 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
   --> $SRC_DIR/core/src/ops/async_function.rs:LL:COL
    |
    = note: the trait cannot be made into an object because it contains the generic associated type `CallFuture`
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFn` for this new enum and using it instead:
+             &F
+             std::boxed::Box<F, A>
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0038]: the trait `AsyncFnMut` cannot be made into an object
@@ -66,6 +83,10 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
   --> $SRC_DIR/core/src/ops/async_function.rs:LL:COL
    |
    = note: the trait cannot be made into an object because it contains the generic associated type `CallMutFuture`
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFnMut` for this new enum and using it instead:
+             &F
+             &mut F
+             std::boxed::Box<F, A>
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0038]: the trait `AsyncFn` cannot be made into an object
@@ -81,6 +102,9 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
   ::: $SRC_DIR/core/src/ops/async_function.rs:LL:COL
    |
    = note: the trait cannot be made into an object because it contains the generic associated type `CallMutFuture`
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFn` for this new enum and using it instead:
+             &F
+             std::boxed::Box<F, A>
 
 error: aborting due to 7 previous errors