chore: fix some clippy lints (#3720)

tokio/src/io/util/lines.rs

@@ -128,7 +128,7 @@ where
             }
         }
 
-        Poll::Ready(Ok(Some(mem::replace(me.buf, String::new()))))
+        Poll::Ready(Ok(Some(mem::take(me.buf))))
     }
 }
 

tokio/src/io/util/read_line.rs

@@ -36,7 +36,7 @@ where
 {
     ReadLine {
         reader,
-        buf: mem::replace(string, String::new()).into_bytes(),
+        buf: mem::take(string).into_bytes(),
         output: string,
         read: 0,
         _pin: PhantomPinned,
@@ -99,7 +99,7 @@ pub(super) fn read_line_internal<R: AsyncBufRead + ?Sized>(
     read: &mut usize,
 ) -> Poll<io::Result<usize>> {
     let io_res = ready!(read_until_internal(reader, cx, b'\n', buf, read));
-    let utf8_res = String::from_utf8(mem::replace(buf, Vec::new()));
+    let utf8_res = String::from_utf8(mem::take(buf));
 
     // At this point both buf and output are empty. The allocation is in utf8_res.
 

tokio/src/io/util/read_to_string.rs

@@ -37,7 +37,7 @@ pub(crate) fn read_to_string<'a, R>(
 where
     R: AsyncRead + ?Sized + Unpin,
 {
-    let buf = mem::replace(string, String::new()).into_bytes();
+    let buf = mem::take(string).into_bytes();
     ReadToString {
         reader,
         buf: VecWithInitialized::new(buf),

tokio/src/io/util/split.rs

@@ -106,7 +106,7 @@ where
             me.buf.pop();
         }
 
-        Poll::Ready(Ok(Some(mem::replace(me.buf, Vec::new()))))
+        Poll::Ready(Ok(Some(mem::take(me.buf))))
     }
 }
 

tokio/src/runtime/blocking/pool.rs

@@ -151,7 +151,7 @@ impl BlockingPool {
         self.spawner.inner.condvar.notify_all();
 
         let last_exited_thread = std::mem::take(&mut shared.last_exiting_thread);
-        let workers = std::mem::replace(&mut shared.worker_threads, HashMap::new());
+        let workers = std::mem::take(&mut shared.worker_threads);
 
         drop(shared);
 

tokio/src/sync/watch.rs

@@ -205,7 +205,7 @@ impl<T> Receiver<T> {
         // not memory access.
         shared.ref_count_rx.fetch_add(1, Relaxed);
 
-        Self { version, shared }
+        Self { shared, version }
     }
 
     /// Returns a reference to the most recently sent value

tokio/src/util/slab.rs

@@ -296,7 +296,7 @@ impl<T> Slab<T> {
 
             // Remove the slots vector from the page. This is done so that the
             // freeing process is done outside of the lock's critical section.
-            let vec = mem::replace(&mut slots.slots, vec![]);
+            let vec = mem::take(&mut slots.slots);
             slots.head = 0;
 
             // Drop the lock so we can drop the vector outside the lock below.