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

Stabilize futures_api

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

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

Author: Centril

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;