10 files changed, 185 insertions, 20 deletions

diff --git a/embassy-executor/Cargo.toml b/embassy-executor/Cargo.toml
index f014ccf30..2dbf2c29a 100644
--- a/embassy-executor/Cargo.toml
+++ b/embassy-executor/Cargo.toml
@@ -59,6 +59,7 @@ avr-device = { version = "0.7.0", optional = true }
 critical-section = { version = "1.1", features = ["std"] }
 trybuild = "1.0"
 embassy-sync = { path = "../embassy-sync" }
+rustversion = "1.0.21"
 
 [features]
 
diff --git a/embassy-executor/tests/ui.rs b/embassy-executor/tests/ui.rs
index ed8228e27..c4a1a601c 100644
--- a/embassy-executor/tests/ui.rs
+++ b/embassy-executor/tests/ui.rs
@@ -17,10 +17,15 @@ fn ui() {
     t.compile_fail("tests/ui/nonstatic_struct_elided.rs");
     t.compile_fail("tests/ui/nonstatic_struct_generic.rs");
     t.compile_fail("tests/ui/not_async.rs");
-    // #[cfg(not(feature = "nightly"))] // output differs on stable and nightly
-    // t.compile_fail("tests/ui/bad_return_impl_trait.rs");
-    #[cfg(feature = "nightly")]
-    t.compile_fail("tests/ui/bad_return_impl_trait_nightly.rs");
+    if rustversion::cfg!(stable) {
+        // output is slightly different on nightly
+        t.compile_fail("tests/ui/bad_return_impl_future.rs");
+        t.compile_fail("tests/ui/return_impl_send.rs");
+    }
+    if cfg!(feature = "nightly") {
+        t.compile_fail("tests/ui/bad_return_impl_future_nightly.rs");
+        t.compile_fail("tests/ui/return_impl_send_nightly.rs");
+    }
     t.compile_fail("tests/ui/self_ref.rs");
     t.compile_fail("tests/ui/self.rs");
     t.compile_fail("tests/ui/type_error.rs");
diff --git a/embassy-executor/tests/ui/bad_return_impl_trait.rs b/embassy-executor/tests/ui/bad_return_impl_future.rs
index baaa7dc5a..baaa7dc5a 100644
--- a/embassy-executor/tests/ui/bad_return_impl_trait.rs
+++ b/embassy-executor/tests/ui/bad_return_impl_future.rs
diff --git a/embassy-executor/tests/ui/bad_return_impl_trait.stderr b/embassy-executor/tests/ui/bad_return_impl_future.stderr
index 9e2df353e..2980fd18b 100644
--- a/embassy-executor/tests/ui/bad_return_impl_trait.stderr
+++ b/embassy-executor/tests/ui/bad_return_impl_future.stderr
@@ -1,5 +1,5 @@
-error[E0277]: task function futures must resolve to `()`
- --> tests/ui/bad_return_impl_trait.rs:5:4
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/bad_return_impl_future.rs:5:4
   |
 4 | #[embassy_executor::task]
   | ------------------------- required by a bound introduced by this call
@@ -16,8 +16,8 @@ note: required by a bound in `task_pool_size`
   |         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
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/bad_return_impl_future.rs:4:1
   |
 4 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
@@ -33,8 +33,8 @@ note: required by a bound in `task_pool_size`
   |            ^^^^^^^^^^^^^^^^^^^^^^^ 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
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/bad_return_impl_future.rs:5:4
   |
 4 | #[embassy_executor::task]
   | ------------------------- required by a bound introduced by this call
@@ -51,8 +51,8 @@ note: required by a bound in `task_pool_align`
   |         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
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/bad_return_impl_future.rs:4:1
   |
 4 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
@@ -68,8 +68,8 @@ note: required by a bound in `task_pool_align`
   |            ^^^^^^^^^^^^^^^^^^^^^^^ 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
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/bad_return_impl_future.rs:5:4
   |
 4 | #[embassy_executor::task]
   | ------------------------- required by a bound introduced by this call
@@ -86,8 +86,8 @@ note: required by a bound in `task_pool_new`
   |         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
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/bad_return_impl_future.rs:4:1
   |
 4 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Future<Output = u32> {__task_task}`
@@ -103,8 +103,8 @@ note: required by a bound in `task_pool_new`
   |            ^^^^^^^^^^^^^^^^^^^^^^^ 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
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/bad_return_impl_future.rs:5:4
   |
 4 | #[embassy_executor::task]
   | ------------------------- required by a bound introduced by this call
@@ -113,7 +113,7 @@ error[E0277]: task function futures must resolve to `()`
   |
   = 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
+ --> tests/ui/bad_return_impl_future.rs:4:1
   |
 4 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `__task_pool_get`
diff --git a/embassy-executor/tests/ui/bad_return_impl_trait_nightly.rs b/embassy-executor/tests/ui/bad_return_impl_future_nightly.rs
index baaa7dc5a..baaa7dc5a 100644
--- a/embassy-executor/tests/ui/bad_return_impl_trait_nightly.rs
+++ b/embassy-executor/tests/ui/bad_return_impl_future_nightly.rs
diff --git a/embassy-executor/tests/ui/bad_return_impl_trait_nightly.stderr b/embassy-executor/tests/ui/bad_return_impl_future_nightly.stderr
index a51251bb8..73ceb989d 100644
--- a/embassy-executor/tests/ui/bad_return_impl_trait_nightly.stderr
+++ b/embassy-executor/tests/ui/bad_return_impl_future_nightly.stderr
@@ -1,5 +1,5 @@
 error[E0277]: task futures must resolve to `()` or `!`
- --> tests/ui/bad_return_impl_trait_nightly.rs:4:1
+ --> tests/ui/bad_return_impl_future_nightly.rs:4:1
   |
 4 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskReturnValue` is not implemented for `u32`
diff --git a/embassy-executor/tests/ui/return_impl_send.rs b/embassy-executor/tests/ui/return_impl_send.rs
new file mode 100644
index 000000000..6ddb0e722
--- /dev/null
+++ b/embassy-executor/tests/ui/return_impl_send.rs
@@ -0,0 +1,6 @@
+#![cfg_attr(feature = "nightly", feature(impl_trait_in_assoc_type))]
+
+#[embassy_executor::task]
+fn task() -> impl Send {}
+
+fn main() {}
diff --git a/embassy-executor/tests/ui/return_impl_send.stderr b/embassy-executor/tests/ui/return_impl_send.stderr
new file mode 100644
index 000000000..7e3e468b8
--- /dev/null
+++ b/embassy-executor/tests/ui/return_impl_send.stderr
@@ -0,0 +1,137 @@
+error[E0277]: task futures must resolve to `()` or `!`
+ --> tests/ui/return_impl_send.rs:4:4
+  |
+3 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+4 | fn task() -> impl Send {}
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Send {__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 futures must resolve to `()` or `!`
+ --> tests/ui/return_impl_send.rs:3:1
+  |
+3 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Send {__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 futures must resolve to `()` or `!`
+ --> tests/ui/return_impl_send.rs:4:4
+  |
+3 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+4 | fn task() -> impl Send {}
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Send {__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 futures must resolve to `()` or `!`
+ --> tests/ui/return_impl_send.rs:3:1
+  |
+3 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Send {__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 futures must resolve to `()` or `!`
+ --> tests/ui/return_impl_send.rs:4:4
+  |
+3 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+4 | fn task() -> impl Send {}
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Send {__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 futures must resolve to `()` or `!`
+ --> tests/ui/return_impl_send.rs:3:1
+  |
+3 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Send {__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 futures must resolve to `()` or `!`
+ --> tests/ui/return_impl_send.rs:4:4
+  |
+3 | #[embassy_executor::task]
+  | ------------------------- required by a bound introduced by this call
+4 | fn task() -> impl Send {}
+  |    ^^^^ the trait `TaskFn<_>` is not implemented for fn item `fn() -> impl Send {__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/return_impl_send.rs:3:1
+  |
+3 | #[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)
+
+error[E0277]: `impl Send` is not a future
+ --> tests/ui/return_impl_send.rs:3:1
+  |
+3 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ `impl Send` is not a future
+  |
+  = help: the trait `Future` is not implemented for `impl Send`
+note: required by a bound in `TaskPool::<F, N>::_spawn_async_fn`
+ --> src/raw/mod.rs
+  |
+  | impl<F: Future + 'static, const N: usize> TaskPool<F, N> {
+  |         ^^^^^^ required by this bound in `TaskPool::<F, N>::_spawn_async_fn`
+...
+  |     pub unsafe fn _spawn_async_fn<FutFn>(&'static self, future: FutFn) -> SpawnToken<impl Sized>
+  |                   --------------- required by a bound in this associated function
+  = 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/return_impl_send_nightly.rs b/embassy-executor/tests/ui/return_impl_send_nightly.rs
new file mode 100644
index 000000000..6ddb0e722
--- /dev/null
+++ b/embassy-executor/tests/ui/return_impl_send_nightly.rs
@@ -0,0 +1,6 @@
+#![cfg_attr(feature = "nightly", feature(impl_trait_in_assoc_type))]
+
+#[embassy_executor::task]
+fn task() -> impl Send {}
+
+fn main() {}
diff --git a/embassy-executor/tests/ui/return_impl_send_nightly.stderr b/embassy-executor/tests/ui/return_impl_send_nightly.stderr
new file mode 100644
index 000000000..de9ba6243
--- /dev/null
+++ b/embassy-executor/tests/ui/return_impl_send_nightly.stderr
@@ -0,0 +1,10 @@
+error[E0277]: `impl Send` is not a future
+ --> tests/ui/return_impl_send_nightly.rs:3:1
+  |
+3 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^
+  | |
+  | `impl Send` is not a future
+  | return type was inferred to be `impl Send` here
+  |
+  = help: the trait `Future` is not implemented for `impl Send`