Auto merge of #70831 - sfackler:shrink-future-stack, r=matthewjasper

Remove a stack frame from .await calls

The stack frames when `.await`ing one async fn from another currently look like this:

```
  12: foo::b::{{closure}}
             at src/main.rs:2
  13: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at /home/sfackler/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/future/mod.rs:66
  14: core::future::poll_with_context
             at /home/sfackler/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/future/mod.rs:84
  15: foo::a::{{closure}}
             at src/main.rs:6
```

Since the move away from using TLS to pass the Context around, it's now easy to remove frame 14 by removing poll_with_context in favor of calling Future::poll directly. This still leaves the `GenFuture` frame, but that seems significantly harder to deal with.

It also improves diagnostics a bit since they no longer talk about the private poll_with_context function.

1 files changed, 2 insertions, 5 deletions

diff --git a/src/libcore/future/mod.rs b/src/libcore/future/mod.rs
index 8dfda7a4a32..a6b769147d0 100644
--- a/src/libcore/future/mod.rs
+++ b/src/libcore/future/mod.rs
@@ -77,9 +77,6 @@ where
 #[unstable(feature = "gen_future", issue = "50547")]
 #[cfg(not(bootstrap))]
 #[inline]
-pub unsafe fn poll_with_context<F>(f: Pin<&mut F>, mut cx: ResumeTy) -> Poll<F::Output>
-where
-    F: Future,
-{
-    F::poll(f, cx.0.as_mut())
+pub unsafe fn get_context<'a, 'b>(cx: ResumeTy) -> &'a mut Context<'b> {
+    &mut *cx.0.as_ptr().cast()
 }