Merge pull request #4023 from 0e4ef622/better-errors

Fix ugly compiler error from task macro

embassy-executor-macros/src/macros/task.rs

@@ -145,42 +145,19 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
     };
     #[cfg(not(feature = "nightly"))]
     let mut task_outer_body = quote! {
-        const fn __task_pool_size<F, Args>(_: F) -> usize
+        const fn __task_pool_get<F, Args, Fut>(_: F) -> &'static #embassy_executor::raw::TaskPool<Fut, POOL_SIZE>
         where
-            F: #embassy_executor::_export::TaskFn<Args>,
-        {
-            ::core::mem::size_of::<
-                #embassy_executor::raw::TaskPool<F::Fut, POOL_SIZE>
-            >()
-        }
-        const fn __task_pool_align<F, Args>(_: F) -> usize
-        where
-            F: #embassy_executor::_export::TaskFn<Args>,
-        {
-            ::core::mem::align_of::<
-                #embassy_executor::raw::TaskPool<F::Fut, POOL_SIZE>
-            >()
-        }
-
-        const fn __task_pool_new<F, Args>(_: F) -> #embassy_executor::raw::TaskPool<F::Fut, POOL_SIZE>
-        where
-            F: #embassy_executor::_export::TaskFn<Args>,
-        {
-            #embassy_executor::raw::TaskPool::new()
-        }
-
-        const fn __task_pool_get<F, Args>(_: F) -> &'static #embassy_executor::raw::TaskPool<F::Fut, POOL_SIZE>
-        where
-            F: #embassy_executor::_export::TaskFn<Args>
+            F: #embassy_executor::_export::TaskFn<Args, Fut = Fut>,
+            Fut: ::core::future::Future + 'static,
         {
             unsafe { &*POOL.get().cast() }
         }
 
         const POOL_SIZE: usize = #pool_size;
         static POOL: #embassy_executor::_export::TaskPoolHolder<
-            {__task_pool_size(#task_inner_ident)},
-            {__task_pool_align(#task_inner_ident)},
-        > = unsafe { ::core::mem::transmute(__task_pool_new(#task_inner_ident)) };
+            {#embassy_executor::_export::task_pool_size::<_, _, _, POOL_SIZE>(#task_inner_ident)},
+            {#embassy_executor::_export::task_pool_align::<_, _, _, POOL_SIZE>(#task_inner_ident)},
+        > = unsafe { ::core::mem::transmute(#embassy_executor::_export::task_pool_new::<_, _, _, POOL_SIZE>(#task_inner_ident)) };
         unsafe { __task_pool_get(#task_inner_ident)._spawn_async_fn(move || #task_inner_ident(#(#full_args,)*)) }
     };
 

embassy-executor/src/lib.rs

@@ -59,6 +59,8 @@ pub mod _export {
     use core::future::Future;
     use core::mem::MaybeUninit;
 
+    use crate::raw::TaskPool;
+
     pub trait TaskFn<Args>: Copy {
         type Fut: Future + 'static;
     }
@@ -116,6 +118,30 @@ pub mod _export {
         }
     }
 
+    pub const fn task_pool_size<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> usize
+    where
+        F: TaskFn<Args, Fut = Fut>,
+        Fut: Future + 'static,
+    {
+        size_of::<TaskPool<Fut, POOL_SIZE>>()
+    }
+
+    pub const fn task_pool_align<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> usize
+    where
+        F: TaskFn<Args, Fut = Fut>,
+        Fut: Future + 'static,
+    {
+        align_of::<TaskPool<Fut, POOL_SIZE>>()
+    }
+
+    pub const fn task_pool_new<F, Args, Fut, const POOL_SIZE: usize>(_: F) -> TaskPool<Fut, POOL_SIZE>
+    where
+        F: TaskFn<Args, Fut = Fut>,
+        Fut: Future + 'static,
+    {
+        TaskPool::new()
+    }
+
     #[allow(private_bounds)]
     #[repr(transparent)]
     pub struct Align<const N: usize>([<Self as Alignment>::Archetype; 0])

embassy-executor/tests/ui.rs

@@ -19,5 +19,6 @@ fn ui() {
     t.compile_fail("tests/ui/not_async.rs");
     t.compile_fail("tests/ui/self_ref.rs");
     t.compile_fail("tests/ui/self.rs");
+    t.compile_fail("tests/ui/type_error.rs");
     t.compile_fail("tests/ui/where_clause.rs");
 }

embassy-executor/tests/ui/type_error.rs

@@ -0,0 +1,8 @@
+#![cfg_attr(feature = "nightly", feature(impl_trait_in_assoc_type))]
+
+#[embassy_executor::task]
+async fn task() {
+    5
+}
+
+fn main() {}

embassy-executor/tests/ui/type_error.stderr

@@ -0,0 +1,7 @@
+error[E0308]: mismatched types
+ --> tests/ui/type_error.rs:5:5
+  |
+4 | async fn task() {
+  |                - help: try adding a return type: `-> i32`
+5 |     5
+  |     ^ expected `()`, found integer