Merge pull request #4443 from Brezak/task-unsafe

executor: mark unsafe tasks as unsafe

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::*;
 
@@ -112,13 +112,11 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
         }
     }
 
-    let task_ident = f.sig.ident.clone();
-    let task_inner_ident = format_ident!("__{}_task", task_ident);
-
-    let mut task_inner = f.clone();
-    let visibility = task_inner.vis.clone();
-    task_inner.vis = syn::Visibility::Inherited;
-    task_inner.sig.ident = task_inner_ident.clone();
+    // Copy the generics + where clause to avoid more spurious errors.
+    let generics = &f.sig.generics;
+    let where_clause = &f.sig.generics.where_clause;
+    let unsafety = &f.sig.unsafety;
+    let visibility = &f.vis;
 
     // assemble the original input arguments,
     // including any attributes that may have
@@ -131,6 +129,64 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
         ));
     }
 
+    let task_ident = f.sig.ident.clone();
+    let task_inner_ident = format_ident!("__{}_task", task_ident);
+
+    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
+        },
+        // Grab the arrow span, why not
+        ReturnType::Type(arrow, typ) if f.sig.asyncness.is_some() => quote! {
+            #arrow impl ::core::future::Future<Output = #typ>
+        },
+        // We assume that if `f` isn't async, it must return `-> impl Future<...>`
+        // This is checked using traits later
+        ReturnType::Type(arrow, typ) => quote! {
+            #arrow #typ
+        },
+    };
+
+    // 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! {
+            #task_inner_function
+
+            // SAFETY: All the preconditions to `#task_ident` apply to
+            //         all contexts `#task_inner_ident` is called in
+            #unsafety {
+                #task_inner_function_ident(#(#full_args,)*)
+            }
+        }
+    } else {
+        quote! {
+            async {::core::todo!()}
+        }
+    };
+
+    let task_inner = quote! {
+        #visibility fn #task_inner_ident #generics (#fargs)
+        #task_inner_future_output
+        #where_clause
+        {
+            #task_inner_body
+        }
+    };
+
     let spawn = if returns_impl_trait {
         quote!(spawn)
     } else {
@@ -173,7 +229,7 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
         unsafe { __task_pool_get(#task_inner_ident).#spawn(move || #task_inner_ident(#(#full_args,)*)) }
     };
 
-    let task_outer_attrs = task_inner.attrs.clone();
+    let task_outer_attrs = &f.attrs;
 
     if !errors.is_empty() {
         task_outer_body = quote! {
@@ -183,10 +239,6 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
         };
     }
 
-    // Copy the generics + where clause to avoid more spurious errors.
-    let generics = &f.sig.generics;
-    let where_clause = &f.sig.generics.where_clause;
-
     let result = quote! {
         // This is the user's task function, renamed.
         // We put it outside the #task_ident fn below, because otherwise
@@ -196,7 +248,7 @@ pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
         #task_inner
 
         #(#task_outer_attrs)*
-        #visibility fn #task_ident #generics (#fargs) -> #embassy_executor::SpawnToken<impl Sized> #where_clause{
+        #visibility #unsafety fn #task_ident #generics (#fargs) -> #embassy_executor::SpawnToken<impl Sized> #where_clause{
             #task_outer_body
         }
 
@@ -213,7 +265,7 @@ fn check_arg_ty(errors: &mut TokenStream, ty: &Type) {
 
     impl<'a, 'ast> Visit<'ast> for Visitor<'a> {
         fn visit_type_reference(&mut self, i: &'ast syn::TypeReference) {
-            // only check for elided lifetime here. If not elided, it's checked by `visit_lifetime`.
+            // Only check for elided lifetime here. If not elided, it's checked by `visit_lifetime`.
             if i.lifetime.is_none() {
                 error(
                     self.errors,

embassy-executor/CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added support for `-> impl Future<Output = ()>` in `#[task]`
 - Fixed `Send` unsoundness with `-> impl Future` tasks
 - Marked `Spawner::for_current_executor` as `unsafe`
+- `#[task]` now properly marks the generated function as unsafe if the task is marked unsafe
 
 ## 0.7.0 - 2025-01-02
 

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;
 }

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());
+    }
+}

embassy-executor/tests/ui.rs

@@ -32,4 +32,7 @@ fn ui() {
     t.compile_fail("tests/ui/self.rs");
     t.compile_fail("tests/ui/type_error.rs");
     t.compile_fail("tests/ui/where_clause.rs");
+    t.compile_fail("tests/ui/unsafe_op_in_unsafe_task.rs");
+
+    t.pass("tests/ui/task_safety_attribute.rs");
 }

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

embassy-executor/tests/ui/nonstatic_struct_elided.stderr

@@ -8,3 +8,17 @@ help: indicate the anonymous lifetime
   |
 6 | async fn task(_x: Foo<'_>) {}
   |                      ++++
+
+error[E0700]: hidden type for `impl Sized` captures lifetime that does not appear in bounds
+ --> tests/ui/nonstatic_struct_elided.rs:5:1
+  |
+5 | #[embassy_executor::task]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ opaque type defined here
+6 | async fn task(_x: Foo) {}
+  |                   --- hidden type `impl Sized` captures the anonymous lifetime defined here
+  |
+  = note: this error originates in the attribute macro `embassy_executor::task` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: add a `use<...>` bound to explicitly capture `'_`
+  |
+5 | #[embassy_executor::task] + use<'_>
+  |                           +++++++++

embassy-executor/tests/ui/task_safety_attribute.rs

@@ -0,0 +1,25 @@
+#![cfg_attr(feature = "nightly", feature(impl_trait_in_assoc_type))]
+#![deny(unused_unsafe)]
+
+use std::mem;
+
+#[embassy_executor::task]
+async fn safe() {}
+
+#[embassy_executor::task]
+async unsafe fn not_safe() {}
+
+#[export_name = "__pender"]
+fn pender(_: *mut ()) {
+    // The test doesn't link if we don't include this.
+    // We never call this anyway.
+}
+
+fn main() {
+    let _forget_me = safe();
+    // SAFETY: not_safe has not safety preconditions
+    let _forget_me2 = unsafe { not_safe() };
+
+    mem::forget(_forget_me);
+    mem::forget(_forget_me2);
+}

embassy-executor/tests/ui/unsafe_op_in_unsafe_task.rs

@@ -0,0 +1,10 @@
+#![cfg_attr(feature = "nightly", feature(impl_trait_in_assoc_type))]
+#![deny(unsafe_op_in_unsafe_fn)]
+
+#[embassy_executor::task]
+async unsafe fn task() {
+    let x = 5;
+    (&x as *const i32).read();
+}
+
+fn main() {}

embassy-executor/tests/ui/unsafe_op_in_unsafe_task.stderr

@@ -0,0 +1,18 @@
+error[E0133]: call to unsafe function `std::ptr::const_ptr::<impl *const T>::read` is unsafe and requires unsafe block
+ --> tests/ui/unsafe_op_in_unsafe_task.rs:7:5
+  |
+7 |     (&x as *const i32).read();
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
+  |
+  = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/unsafe-op-in-unsafe-fn.html>
+  = note: consult the function's documentation for information on how to avoid undefined behavior
+note: an unsafe function restricts its caller, but its body is safe by default
+ --> tests/ui/unsafe_op_in_unsafe_task.rs:5:1
+  |
+5 | async unsafe fn task() {
+  | ^^^^^^^^^^^^^^^^^^^^^^
+note: the lint level is defined here
+ --> tests/ui/unsafe_op_in_unsafe_task.rs:2:9
+  |
+2 | #![deny(unsafe_op_in_unsafe_fn)]
+  |         ^^^^^^^^^^^^^^^^^^^^^^