From 539ff78ebbdedbb75d0faf940e3ee69f5e7f276a Mon Sep 17 00:00:00 2001
From: Brezak <bezak.adamko@gmail.com>
Date: Wed, 23 Jul 2025 19:51:31 +0200
Subject: [PATCH] embassy-executor: explicitly return impl Future in task inner
 task

---
 embassy-executor-macros/src/macros/task.rs    | 19 ++++++++++++++++---
 embassy-executor/src/lib.rs                   |  8 ++++----
 embassy-executor/tests/test.rs                | 11 ++++++++++-
 .../ui/bad_return_impl_future_nightly.stderr  |  2 +-
 4 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/embassy-executor-macros/src/macros/task.rs b/embassy-executor-macros/src/macros/task.rs
index 5b360b128..fc8673743 100644
--- a/embassy-executor-macros/src/macros/task.rs
+++ b/embassy-executor-macros/src/macros/task.rs
@@ -5,7 +5,7 @@ use darling::FromMeta;
 use proc_macro2::{Span, TokenStream};
 use quote::{format_ident, quote};
 use syn::visit::{self, Visit};
-use syn::{Expr, ExprLit, Lit, LitInt, ReturnType, Type};
+use syn::{Expr, ExprLit, Lit, LitInt, ReturnType, Type, Visibility};
 
 use crate::util::*;
 
@@ -135,6 +135,13 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
     let task_inner_future_output = match &f.sig.output {
         ReturnType::Default => quote! {-> impl ::core::future::Future<Output = ()>},
         // Special case the never type since we can't stuff it into a `impl Future<Output = !>`
+        ReturnType::Type(arrow, maybe_never)
+            if f.sig.asyncness.is_some() && matches!(**maybe_never, Type::Never(_)) =>
+        {
+            quote! {
+                #arrow impl ::core::future::Future<Output=#embassy_executor::_export::Never>
+            }
+        }
         ReturnType::Type(arrow, maybe_never) if matches!(**maybe_never, Type::Never(_)) => quote! {
             #arrow #maybe_never
         },
@@ -149,14 +156,20 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
         },
     };
 
+    // We have to rename the function since it might be recursive;
+    let mut task_inner_function = f.clone();
+    let task_inner_function_ident = format_ident!("__{}_task_inner_function", task_ident);
+    task_inner_function.sig.ident = task_inner_function_ident.clone();
+    task_inner_function.vis = Visibility::Inherited;
+
     let task_inner_body = if errors.is_empty() {
         quote! {
-            #f
+            #task_inner_function
 
             // SAFETY: All the preconditions to `#task_ident` apply to
             //         all contexts `#task_inner_ident` is called in
             #unsafety {
-                #task_ident(#(#full_args,)*)
+                #task_inner_function_ident(#(#full_args,)*)
             }
         }
     } else {
diff --git a/embassy-executor/src/lib.rs b/embassy-executor/src/lib.rs
index e174a0594..0747db032 100644
--- a/embassy-executor/src/lib.rs
+++ b/embassy-executor/src/lib.rs
@@ -216,7 +216,7 @@ pub mod _export {
     );
 
     #[allow(dead_code)]
-    trait HasOutput {
+    pub trait HasOutput {
         type Output;
     }
 
@@ -225,7 +225,7 @@ pub mod _export {
     }
 
     #[allow(dead_code)]
-    type Never = <fn() -> ! as HasOutput>::Output;
+    pub type Never = <fn() -> ! as HasOutput>::Output;
 }
 
 /// Implementation details for embassy macros.
@@ -242,7 +242,7 @@ pub mod _export {
     impl TaskReturnValue for Never {}
 
     #[allow(dead_code)]
-    trait HasOutput {
+    pub trait HasOutput {
         type Output;
     }
 
@@ -251,5 +251,5 @@ pub mod _export {
     }
 
     #[allow(dead_code)]
-    type Never = <fn() -> ! as HasOutput>::Output;
+    pub type Never = <fn() -> ! as HasOutput>::Output;
 }
diff --git a/embassy-executor/tests/test.rs b/embassy-executor/tests/test.rs
index c1e7ec5d7..b84d3785a 100644
--- a/embassy-executor/tests/test.rs
+++ b/embassy-executor/tests/test.rs
@@ -7,7 +7,7 @@ use std::sync::{Arc, Mutex};
 use std::task::Poll;
 
 use embassy_executor::raw::Executor;
-use embassy_executor::task;
+use embassy_executor::{task, Spawner};
 
 #[export_name = "__pender"]
 fn __pender(context: *mut ()) {
@@ -317,3 +317,12 @@ fn executor_task_cfg_args() {
         let (_, _, _) = (a, b, c);
     }
 }
+
+#[test]
+fn recursive_task() {
+    #[embassy_executor::task(pool_size = 2)]
+    async fn task1() {
+        let spawner = unsafe { Spawner::for_current_executor().await };
+        spawner.spawn(task1());
+    }
+}
diff --git a/embassy-executor/tests/ui/bad_return_impl_future_nightly.stderr b/embassy-executor/tests/ui/bad_return_impl_future_nightly.stderr
index 73ceb989d..3c3c9503b 100644
--- a/embassy-executor/tests/ui/bad_return_impl_future_nightly.stderr
+++ b/embassy-executor/tests/ui/bad_return_impl_future_nightly.stderr
@@ -7,4 +7,4 @@ error[E0277]: task futures must resolve to `()` or `!`
   = note: use `async fn` or change the return type to `impl Future<Output = ()>`
   = help: the following other types implement trait `TaskReturnValue`:
             ()
-            <fn() -> ! as _export::HasOutput>::Output
+            <fn() -> ! as HasOutput>::Output