Remove unnecessary lets and borrowing from Waker::noop() usage.

`Waker::noop()` now returns a `&'static Waker` reference, so it can be
passed directly to `Context` creation with no temporary lifetime issue.

library/core/tests/async_iter/mod.rs

@@ -7,8 +7,7 @@ fn into_async_iter() {
     let async_iter = async_iter::from_iter(0..3);
     let mut async_iter = pin!(async_iter.into_async_iter());
 
-    let waker = core::task::Waker::noop();
-    let mut cx = &mut core::task::Context::from_waker(&waker);
+    let mut cx = &mut core::task::Context::from_waker(core::task::Waker::noop());
 
     assert_eq!(async_iter.as_mut().poll_next(&mut cx), Poll::Ready(Some(0)));
     assert_eq!(async_iter.as_mut().poll_next(&mut cx), Poll::Ready(Some(1)));

src/tools/miri/tests/pass/async-fn.rs

@@ -76,8 +76,7 @@ async fn unreachable(_: Never) {}
 fn run_fut<T>(fut: impl Future<Output = T>) -> T {
     use std::task::{Context, Poll, Waker};
 
-    let waker = Waker::noop();
-    let mut context = Context::from_waker(&waker);
+    let mut context = Context::from_waker(Waker::noop());
 
     let mut pinned = Box::pin(fut);
     loop {

src/tools/miri/tests/pass/dyn-star.rs

@@ -93,8 +93,7 @@ async fn async_main() {
     let mut fut = async_main();
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match unsafe { Pin::new_unchecked(&mut fut).poll(ctx) } {

src/tools/miri/tests/pass/future-self-referential.rs

@@ -77,8 +77,7 @@ fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
 }
 
 fn run_fut<T>(fut: impl Future<Output = T>) -> T {
-    let waker = Waker::noop();
-    let mut context = Context::from_waker(&waker);
+    let mut context = Context::from_waker(Waker::noop());
 
     let mut pinned = pin!(fut);
     loop {
@@ -90,8 +89,7 @@ fn run_fut<T>(fut: impl Future<Output = T>) -> T {
 }
 
 fn self_referential_box() {
-    let waker = Waker::noop();
-    let cx = &mut Context::from_waker(&waker);
+    let cx = &mut Context::from_waker(Waker::noop());
 
     async fn my_fut() -> i32 {
         let val = 10;

src/tools/miri/tests/pass/issues/issue-miri-2068.rs

@@ -6,8 +6,7 @@
 
 pub fn fuzzing_block_on<O, F: Future<Output = O>>(fut: F) -> O {
     let mut fut = std::pin::pin!(fut);
-    let waker = Waker::noop();
-    let mut context = Context::from_waker(&waker);
+    let mut context = Context::from_waker(Waker::noop());
     loop {
         match fut.as_mut().poll(&mut context) {
             Poll::Ready(v) => return v,

src/tools/miri/tests/pass/move-data-across-await-point.rs

@@ -56,8 +56,7 @@ fn helper(mut data: Vec<u8>, raw_pointer: *mut Vec<u8>) {
 fn run_fut<T>(fut: impl Future<Output = T>) -> T {
     use std::task::{Context, Poll, Waker};
 
-    let waker = Waker::noop();
-    let mut context = Context::from_waker(&waker);
+    let mut context = Context::from_waker(Waker::noop());
 
     let mut pinned = Box::pin(fut);
     loop {

tests/coverage/async.coverage

@@ -117,8 +117,7 @@
    LL|       |    #[coverage(off)]
    LL|       |    pub fn block_on<F: Future>(mut future: F) -> F::Output {
    LL|       |        let mut future = pin!(future);
-   LL|       |        let waker = Waker::noop();
-   LL|       |        let mut context = Context::from_waker(&waker);
+   LL|       |        let mut context = Context::from_waker(Waker::noop());
    LL|       |
    LL|       |        loop {
    LL|       |            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/coverage/async.rs

@@ -110,8 +110,7 @@ mod executor {
     #[coverage(off)]
     pub fn block_on<F: Future>(mut future: F) -> F::Output {
         let mut future = pin!(future);
-        let waker = Waker::noop();
-        let mut context = Context::from_waker(&waker);
+        let mut context = Context::from_waker(Waker::noop());
 
         loop {
             if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/coverage/async2.coverage

@@ -41,8 +41,7 @@
    LL|       |    #[coverage(off)]
    LL|       |    pub fn block_on<F: Future>(mut future: F) -> F::Output {
    LL|       |        let mut future = pin!(future);
-   LL|       |        let waker = Waker::noop();
-   LL|       |        let mut context = Context::from_waker(&waker);
+   LL|       |        let mut context = Context::from_waker(Waker::noop());
    LL|       |
    LL|       |        loop {
    LL|       |            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/coverage/async2.rs

@@ -39,8 +39,7 @@ mod executor {
     #[coverage(off)]
     pub fn block_on<F: Future>(mut future: F) -> F::Output {
         let mut future = pin!(future);
-        let waker = Waker::noop();
-        let mut context = Context::from_waker(&waker);
+        let mut context = Context::from_waker(Waker::noop());
 
         loop {
             if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/coverage/async_block.coverage

@@ -24,8 +24,7 @@
    LL|       |    #[coverage(off)]
    LL|       |    pub fn block_on<F: Future>(mut future: F) -> F::Output {
    LL|       |        let mut future = pin!(future);
-   LL|       |        let waker = Waker::noop();
-   LL|       |        let mut context = Context::from_waker(&waker);
+   LL|       |        let mut context = Context::from_waker(Waker::noop());
    LL|       |
    LL|       |        loop {
    LL|       |            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/coverage/async_block.rs

@@ -23,8 +23,7 @@ mod executor {
     #[coverage(off)]
     pub fn block_on<F: Future>(mut future: F) -> F::Output {
         let mut future = pin!(future);
-        let waker = Waker::noop();
-        let mut context = Context::from_waker(&waker);
+        let mut context = Context::from_waker(Waker::noop());
 
         loop {
             if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/coverage/closure_macro_async.coverage

@@ -54,8 +54,7 @@
    LL|       |    #[coverage(off)]
    LL|       |    pub fn block_on<F: Future>(mut future: F) -> F::Output {
    LL|       |        let mut future = pin!(future);
-   LL|       |        let waker = Waker::noop();
-   LL|       |        let mut context = Context::from_waker(&waker);
+   LL|       |        let mut context = Context::from_waker(Waker::noop());
    LL|       |
    LL|       |        loop {
    LL|       |            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/coverage/closure_macro_async.rs

@@ -53,8 +53,7 @@ mod executor {
     #[coverage(off)]
     pub fn block_on<F: Future>(mut future: F) -> F::Output {
         let mut future = pin!(future);
-        let waker = Waker::noop();
-        let mut context = Context::from_waker(&waker);
+        let mut context = Context::from_waker(Waker::noop());
 
         loop {
             if let Poll::Ready(val) = future.as_mut().poll(&mut context) {

tests/ui/async-await/for-await-passthrough.rs

@@ -25,8 +25,7 @@ async fn real_main() {
 
 fn main() {
     let future = real_main();
-    let waker = std::task::Waker::noop();
-    let mut cx = &mut core::task::Context::from_waker(&waker);
+    let mut cx = &mut core::task::Context::from_waker(std::task::Waker::noop());
     let mut future = core::pin::pin!(future);
     while let core::task::Poll::Pending = future.as_mut().poll(&mut cx) {}
 }

tests/ui/async-await/for-await.rs

@@ -17,8 +17,7 @@ async fn real_main() {
 
 fn main() {
     let future = real_main();
-    let waker = std::task::Waker::noop();
-    let mut cx = &mut core::task::Context::from_waker(&waker);
+    let mut cx = &mut core::task::Context::from_waker(std::task::Waker::noop());
     let mut future = core::pin::pin!(future);
     while let core::task::Poll::Pending = future.as_mut().poll(&mut cx) {}
 }

tests/ui/async-await/in-trait/async-default-fn-overridden.rs

@@ -40,8 +40,7 @@ fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {

tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs

@@ -43,8 +43,7 @@ fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {

tests/ui/async-await/in-trait/dont-project-to-specializable-projection.stderr

@@ -21,7 +21,7 @@ LL |     default async fn foo(_: T) -> &'static str {
    = note: specialization behaves in inconsistent and surprising ways with async functions in traits, and for now is disallowed
 
 error[E0599]: no method named `poll` found for struct `Pin<&mut impl Future<Output = ()>>` in the current scope
-  --> $DIR/dont-project-to-specializable-projection.rs:50:28
+  --> $DIR/dont-project-to-specializable-projection.rs:49:28
    |
 LL |         match fut.as_mut().poll(ctx) {
    |                            ^^^^ method not found in `Pin<&mut impl Future<Output = ()>>`

tests/ui/coroutine/async-gen-yield-ty-is-unit.rs

@@ -11,7 +11,6 @@
 
 pub fn main() {
     let async_iterator = pin!(gen_fn());
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
     async_iterator.poll_next(ctx);
 }

tests/ui/coroutine/async_gen_fn_iter.rs

@@ -74,8 +74,7 @@ fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {

tests/ui/dyn-star/dispatch-on-pin-mut.rs

@@ -19,15 +19,14 @@ async fn async_main() {
 // ------------------------------------------------------------------------- //
 // Implementation Details Below...
 
-use std::task::*;
 use std::pin::pin;
+use std::task::*;
 
 fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {