From a4d4f62a1e0e808ec3dd93e282f517a2f8ad9fa5 Mon Sep 17 00:00:00 2001
From: Matthew Tran <0e4ef622@gmail.com>
Date: Wed, 28 May 2025 22:00:25 -0500
Subject: Allow `-> impl Future<Output = ()>` in #[task]

---
 embassy-executor/src/lib.rs | 47 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

(limited to 'embassy-executor/src')

diff --git a/embassy-executor/src/lib.rs b/embassy-executor/src/lib.rs
index dfe420bab..70abfcc3a 100644
--- a/embassy-executor/src/lib.rs
+++ b/embassy-executor/src/lib.rs
@@ -65,8 +65,17 @@ pub mod _export {
 
     use crate::raw::TaskPool;
 
+    trait TaskReturnValue {}
+    impl TaskReturnValue for () {}
+    impl TaskReturnValue for Never {}
+
+    #[diagnostic::on_unimplemented(
+        message = "task function futures must resolve to `()`",
+        note = "use `async fn` or change the return type to `impl Future<Output = ()>`"
+    )]
+    #[allow(private_bounds)]
     pub trait TaskFn<Args>: Copy {
-        type Fut: Future + 'static;
+        type Fut: Future<Output: TaskReturnValue> + 'static;
     }
 
     macro_rules! task_fn_impl {
@@ -74,7 +83,7 @@ pub mod _export {
             impl<F, Fut, $($Tn,)*> TaskFn<($($Tn,)*)> for F
             where
                 F: Copy + FnOnce($($Tn,)*) -> Fut,
-                Fut: Future + 'static,
+                Fut: Future<Output: TaskReturnValue> + 'static,
             {
                 type Fut = Fut;
             }
@@ -205,4 +214,38 @@ pub mod _export {
         Align268435456: 268435456,
         Align536870912: 536870912,
     );
+
+    #[allow(dead_code)]
+    trait HasOutput {
+        type Output;
+    }
+
+    impl<O> HasOutput for fn() -> O {
+        type Output = O;
+    }
+
+    #[allow(dead_code)]
+    type Never = <fn() -> ! as HasOutput>::Output;
+}
+
+/// Implementation details for embassy macros.
+/// Do not use. Used for macros and HALs only. Not covered by semver guarantees.
+#[doc(hidden)]
+#[cfg(feature = "nightly")]
+pub mod _export {
+    pub trait TaskReturnValue {}
+    impl TaskReturnValue for () {}
+    impl TaskReturnValue for Never {}
+
+    #[allow(dead_code)]
+    trait HasOutput {
+        type Output;
+    }
+
+    impl<O> HasOutput for fn() -> O {
+        type Output = O;
+    }
+
+    #[allow(dead_code)]
+    type Never = <fn() -> ! as HasOutput>::Output;
 }
-- 
cgit 


From b06a708f81d208236763a121797807fd5b48aee6 Mon Sep 17 00:00:00 2001
From: Matthew Tran <0e4ef622@gmail.com>
Date: Thu, 29 May 2025 05:54:25 -0500
Subject: Mention ! in diagnostic

---
 embassy-executor/src/lib.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'embassy-executor/src')

diff --git a/embassy-executor/src/lib.rs b/embassy-executor/src/lib.rs
index 70abfcc3a..e26e8ee7d 100644
--- a/embassy-executor/src/lib.rs
+++ b/embassy-executor/src/lib.rs
@@ -70,7 +70,7 @@ pub mod _export {
     impl TaskReturnValue for Never {}
 
     #[diagnostic::on_unimplemented(
-        message = "task function futures must resolve to `()`",
+        message = "task futures must resolve to `()` or `!`",
         note = "use `async fn` or change the return type to `impl Future<Output = ()>`"
     )]
     #[allow(private_bounds)]
-- 
cgit 


From 0d83fbbb57cf17186a1b8f40f57ef7a35b3e9627 Mon Sep 17 00:00:00 2001
From: Matthew Tran <0e4ef622@gmail.com>
Date: Sun, 1 Jun 2025 10:32:24 -0500
Subject: Add diagnostic::on_unimplemented for nightly

---
 embassy-executor/src/lib.rs | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'embassy-executor/src')

diff --git a/embassy-executor/src/lib.rs b/embassy-executor/src/lib.rs
index e26e8ee7d..e174a0594 100644
--- a/embassy-executor/src/lib.rs
+++ b/embassy-executor/src/lib.rs
@@ -233,6 +233,10 @@ pub mod _export {
 #[doc(hidden)]
 #[cfg(feature = "nightly")]
 pub mod _export {
+    #[diagnostic::on_unimplemented(
+        message = "task futures must resolve to `()` or `!`",
+        note = "use `async fn` or change the return type to `impl Future<Output = ()>`"
+    )]
     pub trait TaskReturnValue {}
     impl TaskReturnValue for () {}
     impl TaskReturnValue for Never {}
-- 
cgit