From 18be370342c9b2a93f1d56b2b674bd2fbdcbb019 Mon Sep 17 00:00:00 2001
From: Yoshua Wuyts <yoshuawuyts@gmail.com>
Date: Sun, 5 Apr 2020 17:50:45 +0200
Subject: [PATCH] Add core::ready! macro

---
 src/libcore/task/mod.rs   |  4 +++
 src/libcore/task/ready.rs | 60 +++++++++++++++++++++++++++++++++++++++
 src/libstd/lib.rs         |  1 +
 3 files changed, 65 insertions(+)
 create mode 100644 src/libcore/task/ready.rs

diff --git a/src/libcore/task/mod.rs b/src/libcore/task/mod.rs
index 27760749c1d4b..3d6f4f5971a62 100644
--- a/src/libcore/task/mod.rs
+++ b/src/libcore/task/mod.rs
@@ -9,3 +9,7 @@ pub use self::poll::Poll;
 mod wake;
 #[stable(feature = "futures_api", since = "1.36.0")]
 pub use self::wake::{Context, RawWaker, RawWakerVTable, Waker};
+
+mod ready;
+#[unstable(feature = "ready_macro", issue = "70922")]
+pub use ready::ready;
diff --git a/src/libcore/task/ready.rs b/src/libcore/task/ready.rs
new file mode 100644
index 0000000000000..d4e733eb2bcf5
--- /dev/null
+++ b/src/libcore/task/ready.rs
@@ -0,0 +1,60 @@
+/// Extracts the successful type of a `Poll<T>`.
+///
+/// This macro bakes in propagation of `Pending` signals by returning early.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(future_readiness_fns)]
+/// #![feature(ready_macro)]
+///
+/// use core::task::{ready, Context, Poll};
+/// use core::future::{self, Future};
+/// use core::pin::Pin;
+///
+/// pub fn do_poll(cx: &mut Context<'_>) -> Poll<()> {
+///     let mut fut = future::ready(42);
+///     let fut = Pin::new(&mut fut);
+///
+///     let num = ready!(fut.poll(cx));
+///     # drop(num);
+///     // ... use num
+///
+///     Poll::Ready(())
+/// }
+/// ```
+///
+/// The `ready!` call expands to:
+///
+/// ```
+/// # #![feature(future_readiness_fns)]
+/// # #![feature(ready_macro)]
+/// #
+/// # use core::task::{Context, Poll};
+/// # use core::future::{self, Future};
+/// # use core::pin::Pin;
+/// #
+/// # pub fn do_poll(cx: &mut Context<'_>) -> Poll<()> {
+///     # let mut fut = future::ready(42);
+///     # let fut = Pin::new(&mut fut);
+///     #
+/// let num = match fut.poll(cx) {
+///     Poll::Ready(t) => t,
+///     Poll::Pending => return Poll::Pending,
+/// };
+///     # drop(num);
+///     # // ... use num
+///     #
+///     # Poll::Ready(())
+/// # }
+/// ```
+#[unstable(feature = "ready_macro", issue = "70922")]
+#[rustc_macro_transparency = "semitransparent"]
+pub macro ready($e:expr) {
+    match $e {
+        $crate::task::Poll::Ready(t) => t,
+        $crate::task::Poll::Pending => {
+            return $crate::task::Poll::Pending;
+        }
+    }
+}
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index bd585d39c242f..939db4bb12e56 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -299,6 +299,7 @@
 #![feature(ptr_internals)]
 #![feature(raw)]
 #![feature(raw_ref_macros)]
+#![feature(ready_macro)]
 #![feature(renamed_spin_loop)]
 #![feature(rustc_attrs)]
 #![feature(rustc_private)]