Allow `-> impl Future<Output = ()>` in #[task]

4 files changed, 147 insertions, 0 deletions

diff --git a/embassy-executor/tests/ui/bad_return_impl_trait.rs b/embassy-executor/tests/ui/bad_return_impl_trait.rs
new file mode 100644
index 000000000..baaa7dc5a
--- /dev/null
+++ b/embassy-executor/tests/ui/bad_return_impl_trait.rs
@@ -0,0 +1,9 @@
+#![cfg_attr(feature = "nightly", feature(impl_trait_in_assoc_type))]
+use core::future::Future;
+
+#[embassy_executor::task]
+fn task() -> impl Future<Output = u32> {
+    async { 5 }
+}
+
+fn main() {}
diff --git a/embassy-executor/tests/ui/bad_return_impl_trait.stderr b/embassy-executor/tests/ui/bad_return_impl_trait.stderr
new file mode 100644
index 000000000..9e2df353e
--- /dev/null
+++ b/embassy-executor/tests/ui/bad_return_impl_trait.stderr
@@ -0,0 +1,120 @@
+error[E0277]: task function futures must resolve to `()`
+ --> tests/ui/bad_return_impl_trait.rs:5:4
+  |
+4 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+5 | fn task() -> impl Future<Output = u32> {
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
+  |
+  = note: use `async fn` or change the return type to `impl Future<Output = ()>`
+note: required by a bound in `task_pool_size`
+ --> src/lib.rs
+  |
+  |     pub const fn task_pool_size<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> usize
+  |                  -------------- required by a bound in this function
+  |     where
+  |         F: TaskFn<Args, Fut = Fut>,
+  |                         ^^^^^^^^^ required by this bound in `task_pool_size`
+
+error[E0277]: task function futures must resolve to `()`
+ --> tests/ui/bad_return_impl_trait.rs:4:1
+  |
+4 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
+  |
+  = note: use `async fn` or change the return type to `impl Future<Output = ()>`
+note: required by a bound in `task_pool_size`
+ --> src/lib.rs
+  |
+  |     pub const fn task_pool_size<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> usize
+  |                  -------------- required by a bound in this function
+  |     where
+  |         F: TaskFn<Args, Fut = Fut>,
+  |            ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `task_pool_size`
+  = note: this error originates in the attribute macro `embassy_executor::task` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: task function futures must resolve to `()`
+ --> tests/ui/bad_return_impl_trait.rs:5:4
+  |
+4 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+5 | fn task() -> impl Future<Output = u32> {
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
+  |
+  = note: use `async fn` or change the return type to `impl Future<Output = ()>`
+note: required by a bound in `task_pool_align`
+ --> src/lib.rs
+  |
+  |     pub const fn task_pool_align<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> usize
+  |                  --------------- required by a bound in this function
+  |     where
+  |         F: TaskFn<Args, Fut = Fut>,
+  |                         ^^^^^^^^^ required by this bound in `task_pool_align`
+
+error[E0277]: task function futures must resolve to `()`
+ --> tests/ui/bad_return_impl_trait.rs:4:1
+  |
+4 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
+  |
+  = note: use `async fn` or change the return type to `impl Future<Output = ()>`
+note: required by a bound in `task_pool_align`
+ --> src/lib.rs
+  |
+  |     pub const fn task_pool_align<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> usize
+  |                  --------------- required by a bound in this function
+  |     where
+  |         F: TaskFn<Args, Fut = Fut>,
+  |            ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `task_pool_align`
+  = note: this error originates in the attribute macro `embassy_executor::task` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: task function futures must resolve to `()`
+ --> tests/ui/bad_return_impl_trait.rs:5:4
+  |
+4 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+5 | fn task() -> impl Future<Output = u32> {
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
+  |
+  = note: use `async fn` or change the return type to `impl Future<Output = ()>`
+note: required by a bound in `task_pool_new`
+ --> src/lib.rs
+  |
+  |     pub const fn task_pool_new<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> TaskPool<Fut, POOL_SIZE>
+  |                  ------------- required by a bound in this function
+  |     where
+  |         F: TaskFn<Args, Fut = Fut>,
+  |                         ^^^^^^^^^ required by this bound in `task_pool_new`
+
+error[E0277]: task function futures must resolve to `()`
+ --> tests/ui/bad_return_impl_trait.rs:4:1
+  |
+4 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
+  |
+  = note: use `async fn` or change the return type to `impl Future<Output = ()>`
+note: required by a bound in `task_pool_new`
+ --> src/lib.rs
+  |
+  |     pub const fn task_pool_new<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> TaskPool<Fut, POOL_SIZE>
+  |                  ------------- required by a bound in this function
+  |     where
+  |         F: TaskFn<Args, Fut = Fut>,
+  |            ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `task_pool_new`
+  = note: this error originates in the attribute macro `embassy_executor::task` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: task function futures must resolve to `()`
+ --> tests/ui/bad_return_impl_trait.rs:5:4
+  |
+4 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+5 | fn task() -> impl Future<Output = u32> {
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
+  |
+  = note: use `async fn` or change the return type to `impl Future<Output = ()>`
+note: required by a bound in `__task_pool_get`
+ --> tests/ui/bad_return_impl_trait.rs:4:1
+  |
+4 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `__task_pool_get`
+  = note: this error originates in the attribute macro `embassy_executor::task` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/embassy-executor/tests/ui/bad_return_impl_trait_nightly.rs b/embassy-executor/tests/ui/bad_return_impl_trait_nightly.rs
new file mode 100644
index 000000000..baaa7dc5a
--- /dev/null
+++ b/embassy-executor/tests/ui/bad_return_impl_trait_nightly.rs
@@ -0,0 +1,9 @@
+#![cfg_attr(feature = "nightly", feature(impl_trait_in_assoc_type))]
+use core::future::Future;
+
+#[embassy_executor::task]
+fn task() -> impl Future<Output = u32> {
+    async { 5 }
+}
+
+fn main() {}
diff --git a/embassy-executor/tests/ui/bad_return_impl_trait_nightly.stderr b/embassy-executor/tests/ui/bad_return_impl_trait_nightly.stderr
new file mode 100644
index 000000000..21e20d5c0
--- /dev/null
+++ b/embassy-executor/tests/ui/bad_return_impl_trait_nightly.stderr
@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `u32: TaskReturnValue` is not satisfied
+ --> tests/ui/bad_return_impl_trait_nightly.rs:4:1
+  |
+4 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskReturnValue` is not implemented for `u32`
+  |
+  = help: the following other types implement trait `TaskReturnValue`:
+            ()
+            <fn() -> ! as _export::HasOutput>::Output