Auto merge of #74493 - Manishearth:rollup-ust7yr4, r=Manishearth

Rollup of 7 pull requests

Successful merges:

 - #70817 (Add core::task::ready! macro)
 - #73762 (Document the trait keyword)
 - #74021 (impl Index<RangeFrom> for CStr)
 - #74071 (rustc_metadata: Make crate loading fully speculative)
 - #74445 (add test for #62878)
 - #74459 (Make unreachable_unchecked a const fn)
 - #74478 (Revert "Use an UTF-8 locale for the linker.")

Failed merges:

r? @ghost

1 files changed, 60 insertions, 0 deletions

diff --git a/src/libcore/task/ready.rs b/src/libcore/task/ready.rs
new file mode 100644
index 00000000000..d4e733eb2bc
--- /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;
+        }
+    }
+}