Rollup merge of rust-lang#59739 - cramertj:stabilize, r=withoutboats

Stabilize futures_api

cc rust-lang#59725.
Based on rust-lang#59733 and rust-lang#59119 -- only the last two commits here are relevant.

r? @withoutboats , @oli-obk for the introduction of `rustc_allow_const_fn_ptr`.

src/liballoc/boxed.rs

@@ -911,7 +911,7 @@ impl<G: ?Sized + Generator> Generator for Pin<Box<G>> {
     }
 }
 
-#[unstable(feature = "futures_api", issue = "50547")]
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl<F: ?Sized + Future + Unpin> Future for Box<F> {
     type Output = F::Output;
 

src/liballoc/lib.rs

@@ -85,7 +85,6 @@
 #![feature(fmt_internals)]
 #![feature(fn_traits)]
 #![feature(fundamental)]
-#![feature(futures_api)]
 #![feature(lang_items)]
 #![feature(libc)]
 #![feature(needs_allocator)]

src/libcore/future/future.rs

@@ -1,6 +1,4 @@
-#![unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
+#![stable(feature = "futures_api", since = "1.36.0")]
 
 use crate::marker::Unpin;
 use crate::ops;
@@ -26,8 +24,10 @@ use crate::task::{Context, Poll};
 /// `await!` the value.
 #[doc(spotlight)]
 #[must_use = "futures do nothing unless polled"]
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub trait Future {
     /// The type of value produced on completion.
+    #[stable(feature = "futures_api", since = "1.36.0")]
     type Output;
 
     /// Attempt to resolve the future to a final value, registering
@@ -92,9 +92,11 @@ pub trait Future {
     /// [`Context`]: ../task/struct.Context.html
     /// [`Waker`]: ../task/struct.Waker.html
     /// [`Waker::wake`]: ../task/struct.Waker.html#method.wake
+    #[stable(feature = "futures_api", since = "1.36.0")]
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl<F: ?Sized + Future + Unpin> Future for &mut F {
     type Output = F::Output;
 
@@ -103,6 +105,7 @@ impl<F: ?Sized + Future + Unpin> Future for &mut F {
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl<P> Future for Pin<P>
 where
     P: Unpin + ops::DerefMut,

src/libcore/future/mod.rs

@@ -1,8 +1,7 @@
-#![unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
+#![stable(feature = "futures_api", since = "1.36.0")]
 
 //! Asynchronous values.
 
 mod future;
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub use self::future::Future;

src/libcore/task/mod.rs

@@ -1,11 +1,11 @@
-#![unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
+#![stable(feature = "futures_api", since = "1.36.0")]
 
 //! Types and Traits for working with asynchronous tasks.
 
 mod poll;
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub use self::poll::Poll;
 
 mod wake;
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub use self::wake::{Context, Waker, RawWaker, RawWakerVTable};

src/libcore/task/poll.rs

@@ -1,6 +1,4 @@
-#![unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
+#![stable(feature = "futures_api", since = "1.36.0")]
 
 use crate::ops::Try;
 use crate::result::Result;
@@ -9,20 +7,27 @@ use crate::result::Result;
 /// scheduled to receive a wakeup instead.
 #[must_use = "this `Poll` may be a `Pending` variant, which should be handled"]
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub enum Poll<T> {
     /// Represents that a value is immediately ready.
-    Ready(T),
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    Ready(
+        #[stable(feature = "futures_api", since = "1.36.0")]
+        T
+    ),
 
     /// Represents that a value is not ready yet.
     ///
     /// When a function returns `Pending`, the function *must* also
     /// ensure that the current task is scheduled to be awoken when
     /// progress can be made.
+    #[stable(feature = "futures_api", since = "1.36.0")]
     Pending,
 }
 
 impl<T> Poll<T> {
     /// Changes the ready value of this `Poll` with the closure provided.
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn map<U, F>(self, f: F) -> Poll<U>
         where F: FnOnce(T) -> U
     {
@@ -34,6 +39,7 @@ impl<T> Poll<T> {
 
     /// Returns `true` if this is `Poll::Ready`
     #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn is_ready(&self) -> bool {
         match *self {
             Poll::Ready(_) => true,
@@ -43,13 +49,15 @@ impl<T> Poll<T> {
 
     /// Returns `true` if this is `Poll::Pending`
     #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn is_pending(&self) -> bool {
         !self.is_ready()
     }
 }
 
 impl<T, E> Poll<Result<T, E>> {
     /// Changes the success value of this `Poll` with the closure provided.
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>
         where F: FnOnce(T) -> U
     {
@@ -61,6 +69,7 @@ impl<T, E> Poll<Result<T, E>> {
     }
 
     /// Changes the error value of this `Poll` with the closure provided.
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>
         where F: FnOnce(E) -> U
     {
@@ -72,12 +81,14 @@ impl<T, E> Poll<Result<T, E>> {
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl<T> From<T> for Poll<T> {
     fn from(t: T) -> Poll<T> {
         Poll::Ready(t)
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl<T, E> Try for Poll<Result<T, E>> {
     type Ok = Poll<T>;
     type Error = E;
@@ -102,6 +113,7 @@ impl<T, E> Try for Poll<Result<T, E>> {
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl<T, E> Try for Poll<Option<Result<T, E>>> {
     type Ok = Poll<Option<T>>;
     type Error = E;

src/libcore/task/wake.rs

@@ -1,6 +1,4 @@
-#![unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
+#![stable(feature = "futures_api", since = "1.36.0")]
 
 use crate::fmt;
 use crate::marker::{PhantomData, Unpin};
@@ -13,6 +11,7 @@ use crate::marker::{PhantomData, Unpin};
 /// It consists of a data pointer and a [virtual function pointer table (vtable)][vtable] that
 /// customizes the behavior of the `RawWaker`.
 #[derive(PartialEq, Debug)]
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub struct RawWaker {
     /// A data pointer, which can be used to store arbitrary data as required
     /// by the executor. This could be e.g. a type-erased pointer to an `Arc`
@@ -37,9 +36,7 @@ impl RawWaker {
     /// from a `RawWaker`. For each operation on the `Waker`, the associated
     /// function in the `vtable` of the underlying `RawWaker` will be called.
     #[rustc_promotable]
-    #[unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub const fn new(data: *const (), vtable: &'static RawWakerVTable) -> RawWaker {
         RawWaker {
             data,
@@ -58,6 +55,7 @@ impl RawWaker {
 /// pointer of a properly constructed [`RawWaker`] object from inside the
 /// [`RawWaker`] implementation. Calling one of the contained functions using
 /// any other `data` pointer will cause undefined behavior.
+#[stable(feature = "futures_api", since = "1.36.0")]
 #[derive(PartialEq, Copy, Clone, Debug)]
 pub struct RawWakerVTable {
     /// This function will be called when the [`RawWaker`] gets cloned, e.g. when
@@ -131,9 +129,14 @@ impl RawWakerVTable {
     /// resources that are associated with this instance of a [`RawWaker`] and
     /// associated task.
     #[rustc_promotable]
-    #[unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
+    #[cfg_attr(stage0, unstable(feature = "futures_api_const_fn_ptr", issue = "50547"))]
+    #[cfg_attr(not(stage0), stable(feature = "futures_api", since = "1.36.0"))]
+    // `rustc_allow_const_fn_ptr` is a hack that should not be used anywhere else
+    // without first consulting with T-Lang.
+    //
+    // FIXME: remove whenever we have a stable way to accept fn pointers from const fn
+    // (see https://github.com/rust-rfcs/const-eval/issues/19#issuecomment-472799062)
+    #[cfg_attr(not(stage0), rustc_allow_const_fn_ptr)]
     pub const fn new(
         clone: unsafe fn(*const ()) -> RawWaker,
         wake: unsafe fn(*const ()),
@@ -153,6 +156,7 @@ impl RawWakerVTable {
 ///
 /// Currently, `Context` only serves to provide access to a `&Waker`
 /// which can be used to wake the current task.
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub struct Context<'a> {
     waker: &'a Waker,
     // Ensure we future-proof against variance changes by forcing
@@ -164,6 +168,7 @@ pub struct Context<'a> {
 
 impl<'a> Context<'a> {
     /// Create a new `Context` from a `&Waker`.
+    #[stable(feature = "futures_api", since = "1.36.0")]
     #[inline]
     pub fn from_waker(waker: &'a Waker) -> Self {
         Context {
@@ -173,12 +178,14 @@ impl<'a> Context<'a> {
     }
 
     /// Returns a reference to the `Waker` for the current task.
+    #[stable(feature = "futures_api", since = "1.36.0")]
     #[inline]
     pub fn waker(&self) -> &'a Waker {
         &self.waker
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl fmt::Debug for Context<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Context")
@@ -195,17 +202,22 @@ impl fmt::Debug for Context<'_> {
 ///
 /// Implements [`Clone`], [`Send`], and [`Sync`].
 #[repr(transparent)]
+#[stable(feature = "futures_api", since = "1.36.0")]
 pub struct Waker {
     waker: RawWaker,
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl Unpin for Waker {}
+#[stable(feature = "futures_api", since = "1.36.0")]
 unsafe impl Send for Waker {}
+#[stable(feature = "futures_api", since = "1.36.0")]
 unsafe impl Sync for Waker {}
 
 impl Waker {
     /// Wake up the task associated with this `Waker`.
     #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn wake(self) {
         // The actual wakeup call is delegated through a virtual function call
         // to the implementation which is defined by the executor.
@@ -227,6 +239,7 @@ impl Waker {
     /// where an owned `Waker` is available. This method should be preferred to
     /// calling `waker.clone().wake()`.
     #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn wake_by_ref(&self) {
         // The actual wakeup call is delegated through a virtual function call
         // to the implementation which is defined by the executor.
@@ -243,6 +256,7 @@ impl Waker {
     ///
     /// This function is primarily used for optimization purposes.
     #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn will_wake(&self, other: &Waker) -> bool {
         self.waker == other.waker
     }
@@ -253,13 +267,15 @@ impl Waker {
     /// in [`RawWaker`]'s and [`RawWakerVTable`]'s documentation is not upheld.
     /// Therefore this method is unsafe.
     #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
     pub unsafe fn from_raw(waker: RawWaker) -> Waker {
         Waker {
             waker,
         }
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl Clone for Waker {
     #[inline]
     fn clone(&self) -> Self {
@@ -272,6 +288,7 @@ impl Clone for Waker {
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl Drop for Waker {
     #[inline]
     fn drop(&mut self) {
@@ -282,6 +299,7 @@ impl Drop for Waker {
     }
 }
 
+#[stable(feature = "futures_api", since = "1.36.0")]
 impl fmt::Debug for Waker {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let vtable_ptr = self.waker.vtable as *const RawWakerVTable;

src/librustc/ich/impls_syntax.rs

@@ -121,6 +121,7 @@ impl_stable_hash_for!(struct ::syntax::attr::Stability {
     feature,
     rustc_depr,
     promotable,
+    allow_const_fn_ptr,
     const_stability
 });
 

src/librustc/middle/stability.rs

@@ -441,6 +441,7 @@ impl<'a, 'tcx> Index<'tcx> {
                     rustc_depr: None,
                     const_stability: None,
                     promotable: false,
+                    allow_const_fn_ptr: false,
                 });
                 annotator.parent_stab = Some(stability);
             }

src/librustc/query/mod.rs

@@ -235,6 +235,8 @@ rustc_queries! {
         /// constructor function).
         query is_promotable_const_fn(_: DefId) -> bool {}
 
+        query const_fn_is_allowed_fn_ptr(_: DefId) -> bool {}
+
         /// True if this is a foreign item (i.e., linked via `extern { ... }`).
         query is_foreign_item(_: DefId) -> bool {}
 

src/librustc/ty/constness.rs

@@ -95,9 +95,16 @@ pub fn provide<'tcx>(providers: &mut Providers<'tcx>) {
         }
     }
 
+    fn const_fn_is_allowed_fn_ptr<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
+        tcx.is_const_fn(def_id) &&
+            tcx.lookup_stability(def_id)
+                .map(|stab| stab.allow_const_fn_ptr).unwrap_or(false)
+    }
+
     *providers = Providers {
         is_const_fn_raw,
         is_promotable_const_fn,
+        const_fn_is_allowed_fn_ptr,
         ..*providers
     };
 }