Auto merge of #11698 - a1phyr:waker_clone_and_wake, r=y21

Add `waker_clone_and_wake` lint to check needless `Waker` clones

Check for patterns of `waker.clone().wake()` and replace them with `waker.wake_by_ref()`.

An alternative name could be `waker_clone_then_wake`

changelog: [ `waker_clone_wake`]: new lint

tests/ui/waker_clone_wake.fixed

@@ -0,0 +1,29 @@
+#[derive(Clone)]
+pub struct Custom;
+
+impl Custom {
+    pub fn wake(self) {}
+}
+
+macro_rules! mac {
+    ($cx:ident) => {
+        $cx.waker()
+    };
+}
+
+pub fn wake(cx: &mut std::task::Context) {
+    cx.waker().wake_by_ref();
+
+    mac!(cx).wake_by_ref();
+}
+
+pub fn no_lint(cx: &mut std::task::Context, c: &Custom) {
+    c.clone().wake();
+
+    let w = cx.waker().clone();
+    w.wake();
+
+    cx.waker().clone().wake_by_ref();
+}
+
+fn main() {}

tests/ui/waker_clone_wake.rs

@@ -0,0 +1,29 @@
+#[derive(Clone)]
+pub struct Custom;
+
+impl Custom {
+    pub fn wake(self) {}
+}
+
+macro_rules! mac {
+    ($cx:ident) => {
+        $cx.waker()
+    };
+}
+
+pub fn wake(cx: &mut std::task::Context) {
+    cx.waker().clone().wake();
+
+    mac!(cx).clone().wake();
+}
+
+pub fn no_lint(cx: &mut std::task::Context, c: &Custom) {
+    c.clone().wake();
+
+    let w = cx.waker().clone();
+    w.wake();
+
+    cx.waker().clone().wake_by_ref();
+}
+
+fn main() {}

tests/ui/waker_clone_wake.stderr

@@ -0,0 +1,17 @@
+error: cloning a `Waker` only to wake it
+  --> $DIR/waker_clone_wake.rs:15:5
+   |
+LL |     cx.waker().clone().wake();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `cx.waker().wake_by_ref()`
+   |
+   = note: `-D clippy::waker-clone-wake` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::waker_clone_wake)]`
+
+error: cloning a `Waker` only to wake it
+  --> $DIR/waker_clone_wake.rs:17:5
+   |
+LL |     mac!(cx).clone().wake();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `mac!(cx).wake_by_ref()`
+
+error: aborting due to 2 previous errors
+