Add Context::ext

library/core/src/task/wake.rs

@@ -2,6 +2,7 @@
 
 use crate::mem::transmute;
 
+use crate::any::Any;
 use crate::fmt;
 use crate::marker::PhantomData;
 use crate::ptr;
@@ -220,6 +221,12 @@ impl RawWakerVTable {
     }
 }
 
+#[derive(Debug)]
+enum ExtData<'a> {
+    Some(&'a mut dyn Any),
+    None(()),
+}
+
 /// The context of an asynchronous task.
 ///
 /// Currently, `Context` only serves to provide access to a [`&Waker`](Waker)
@@ -229,6 +236,7 @@ impl RawWakerVTable {
 pub struct Context<'a> {
     waker: &'a Waker,
     local_waker: &'a LocalWaker,
+    ext: ExtData<'a>,
     // Ensure we future-proof against variance changes by forcing
     // the lifetime to be invariant (argument-position lifetimes
     // are contravariant while return-position lifetimes are
@@ -257,13 +265,25 @@ impl<'a> Context<'a> {
     pub const fn waker(&self) -> &'a Waker {
         &self.waker
     }
+
     /// Returns a reference to the [`LocalWaker`] for the current task.
     #[inline]
     #[unstable(feature = "local_waker", issue = "118959")]
     #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
     pub const fn local_waker(&self) -> &'a LocalWaker {
         &self.local_waker
     }
+
+    /// Returns a reference to the extension data for the current task.
+    #[inline]
+    #[unstable(feature = "context_ext", issue = "123392")]
+    #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
+    pub const fn ext(&mut self) -> &mut dyn Any {
+        match &mut self.ext {
+            ExtData::Some(data) => *data,
+            ExtData::None(unit) => unit,
+        }
+    }
 }
 
 #[stable(feature = "futures_api", since = "1.36.0")]
@@ -300,6 +320,7 @@ impl fmt::Debug for Context<'_> {
 pub struct ContextBuilder<'a> {
     waker: &'a Waker,
     local_waker: &'a LocalWaker,
+    ext: ExtData<'a>,
     // Ensure we future-proof against variance changes by forcing
     // the lifetime to be invariant (argument-position lifetimes
     // are contravariant while return-position lifetimes are
@@ -318,7 +339,39 @@ impl<'a> ContextBuilder<'a> {
     pub const fn from_waker(waker: &'a Waker) -> Self {
         // SAFETY: LocalWaker is just Waker without thread safety
         let local_waker = unsafe { transmute(waker) };
-        Self { waker: waker, local_waker, _marker: PhantomData, _marker2: PhantomData }
+        Self {
+            waker: waker,
+            local_waker,
+            ext: ExtData::None(()),
+            _marker: PhantomData,
+            _marker2: PhantomData,
+        }
+    }
+
+    /// Create a ContextBuilder from an existing Context.
+    #[inline]
+    #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
+    #[unstable(feature = "context_ext", issue = "123392")]
+    pub const fn from(cx: &'a mut Context<'_>) -> Self {
+        let ext = match &mut cx.ext {
+            ExtData::Some(ext) => ExtData::Some(*ext),
+            ExtData::None(()) => ExtData::None(()),
+        };
+        Self {
+            waker: cx.waker,
+            local_waker: cx.local_waker,
+            ext,
+            _marker: PhantomData,
+            _marker2: PhantomData,
+        }
+    }
+
+    /// This method is used to set the value for the waker on `Context`.
+    #[inline]
+    #[unstable(feature = "context_ext", issue = "123392")]
+    #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
+    pub const fn waker(self, waker: &'a Waker) -> Self {
+        Self { waker, ..self }
     }
 
     /// This method is used to set the value for the local waker on `Context`.
@@ -329,13 +382,21 @@ impl<'a> ContextBuilder<'a> {
         Self { local_waker, ..self }
     }
 
+    /// This method is used to set the value for the extension data on `Context`.
+    #[inline]
+    #[unstable(feature = "context_ext", issue = "123392")]
+    #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
+    pub const fn ext(self, data: &'a mut dyn Any) -> Self {
+        Self { ext: ExtData::Some(data), ..self }
+    }
+
     /// Builds the `Context`.
     #[inline]
     #[unstable(feature = "local_waker", issue = "118959")]
     #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
     pub const fn build(self) -> Context<'a> {
-        let ContextBuilder { waker, local_waker, _marker, _marker2 } = self;
-        Context { waker, local_waker, _marker, _marker2 }
+        let ContextBuilder { waker, local_waker, ext, _marker, _marker2 } = self;
+        Context { waker, local_waker, ext, _marker, _marker2 }
     }
 }
 

tests/ui/async-await/async-is-unwindsafe.rs

@@ -11,6 +11,7 @@ fn main() {
 
     is_unwindsafe(async {
         //~^ ERROR the type `&mut Context<'_>` may not be safely transferred across an unwind boundary
+        //~| ERROR the type `&mut (dyn Any + 'static)` may not be safely transferred across an unwind boundary
         use std::ptr::null;
         use std::task::{Context, RawWaker, RawWakerVTable, Waker};
         let waker = unsafe {

tests/ui/async-await/async-is-unwindsafe.stderr

@@ -6,19 +6,18 @@ LL |        is_unwindsafe(async {
    |  |_____|
    | ||
 LL | ||
+LL | ||
 LL | ||         use std::ptr::null;
-LL | ||         use std::task::{Context, RawWaker, RawWakerVTable, Waker};
 ...  ||
 LL | ||         drop(cx_ref);
 LL | ||     });
    | ||_____-^ `&mut Context<'_>` may not be safely transferred across an unwind boundary
    |  |_____|
-   |        within this `{async block@$DIR/async-is-unwindsafe.rs:12:19: 29:6}`
+   |        within this `{async block@$DIR/async-is-unwindsafe.rs:12:19: 30:6}`
    |
-   = help: within `{async block@$DIR/async-is-unwindsafe.rs:12:19: 29:6}`, the trait `UnwindSafe` is not implemented for `&mut Context<'_>`, which is required by `{async block@$DIR/async-is-unwindsafe.rs:12:19: 29:6}: UnwindSafe`
-   = note: `UnwindSafe` is implemented for `&Context<'_>`, but not for `&mut Context<'_>`
+   = help: within `{async block@$DIR/async-is-unwindsafe.rs:12:19: 30:6}`, the trait `UnwindSafe` is not implemented for `&mut Context<'_>`, which is required by `{async block@$DIR/async-is-unwindsafe.rs:12:19: 30:6}: UnwindSafe`
 note: future does not implement `UnwindSafe` as this value is used across an await
-  --> $DIR/async-is-unwindsafe.rs:25:18
+  --> $DIR/async-is-unwindsafe.rs:26:18
    |
 LL |         let cx_ref = &mut cx;
    |             ------ has type `&mut Context<'_>` which does not implement `UnwindSafe`
@@ -31,6 +30,38 @@ note: required by a bound in `is_unwindsafe`
 LL | fn is_unwindsafe(_: impl std::panic::UnwindSafe) {}
    |                          ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `is_unwindsafe`
 
-error: aborting due to 1 previous error
+error[E0277]: the type `&mut (dyn Any + 'static)` may not be safely transferred across an unwind boundary
+  --> $DIR/async-is-unwindsafe.rs:12:5
+   |
+LL |        is_unwindsafe(async {
+   |   _____^_____________-
+   |  |_____|
+   | ||
+LL | ||
+LL | ||
+LL | ||         use std::ptr::null;
+...  ||
+LL | ||         drop(cx_ref);
+LL | ||     });
+   | ||_____-^ `&mut (dyn Any + 'static)` may not be safely transferred across an unwind boundary
+   |  |_____|
+   |        within this `{async block@$DIR/async-is-unwindsafe.rs:12:19: 30:6}`
+   |
+   = help: within `{async block@$DIR/async-is-unwindsafe.rs:12:19: 30:6}`, the trait `UnwindSafe` is not implemented for `&mut (dyn Any + 'static)`, which is required by `{async block@$DIR/async-is-unwindsafe.rs:12:19: 30:6}: UnwindSafe`
+note: future does not implement `UnwindSafe` as this value is used across an await
+  --> $DIR/async-is-unwindsafe.rs:26:18
+   |
+LL |         let mut cx = Context::from_waker(&waker);
+   |             ------ has type `Context<'_>` which does not implement `UnwindSafe`
+...
+LL |         async {}.await; // this needs an inner await point
+   |                  ^^^^^ await occurs here, with `mut cx` maybe used later
+note: required by a bound in `is_unwindsafe`
+  --> $DIR/async-is-unwindsafe.rs:3:26
+   |
+LL | fn is_unwindsafe(_: impl std::panic::UnwindSafe) {}
+   |                          ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `is_unwindsafe`
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.