Add core::future::IntoFuture

This patch adds `core::future::IntoFuture`. However unlike earlier PRs this patch does not integrate it into the `async/.await` lowering. That integration should be done in a follow-up PR.

2 files changed, 31 insertions, 0 deletions

diff --git a/src/libcore/future/into_future.rs b/src/libcore/future/into_future.rs
new file mode 100644
index 00000000000..4020c254446
--- /dev/null
+++ b/src/libcore/future/into_future.rs
@@ -0,0 +1,27 @@
+use crate::future::Future;
+
+/// Conversion into a `Future`.
+#[unstable(feature = "into_future", issue = "67644")]
+pub trait IntoFuture {
+    /// The output that the future will produce on completion.
+    #[unstable(feature = "into_future", issue = "67644")]
+    type Output;
+
+    /// Which kind of future are we turning this into?
+    #[unstable(feature = "into_future", issue = "67644")]
+    type Future: Future<Output = Self::Output>;
+
+    /// Creates a future from a value.
+    #[unstable(feature = "into_future", issue = "67644")]
+    fn into_future(self) -> Self::Future;
+}
+
+#[unstable(feature = "into_future", issue = "67644")]
+impl<F: Future> IntoFuture for F {
+    type Output = F::Output;
+    type Future = F;
+
+    fn into_future(self) -> Self::Future {
+        self
+    }
+}
diff --git a/src/libcore/future/mod.rs b/src/libcore/future/mod.rs
index b5a102916a0..6f6009b47e6 100644
--- a/src/libcore/future/mod.rs
+++ b/src/libcore/future/mod.rs
@@ -10,12 +10,16 @@ use crate::{
 };
 
 mod future;
+mod into_future;
 mod pending;
 mod ready;
 
 #[stable(feature = "futures_api", since = "1.36.0")]
 pub use self::future::Future;
 
+#[unstable(feature = "into_future", issue = "67644")]
+pub use into_future::IntoFuture;
+
 #[unstable(feature = "future_readiness_fns", issue = "70921")]
 pub use pending::{pending, Pending};
 #[unstable(feature = "future_readiness_fns", issue = "70921")]