Fix unused_mut warning in nightly

src/io/stderr.rs

@@ -89,11 +89,12 @@ enum Operation {
 
 impl Write for Stderr {
     fn poll_write(
-        mut self: Pin<&mut Self>,
+        self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        let state = &mut *self.0.lock().unwrap();
+        let mut state_guard = self.0.lock().unwrap();
+        let state = &mut *state_guard;
 
         loop {
             match state {
@@ -137,8 +138,9 @@ impl Write for Stderr {
         }
     }
 
-    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        let state = &mut *self.0.lock().unwrap();
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let mut state_guard = self.0.lock().unwrap();
+        let state = &mut *state_guard;
 
         loop {
             match state {

src/io/stdin.rs

@@ -149,11 +149,12 @@ impl Stdin {
 
 impl Read for Stdin {
     fn poll_read(
-        mut self: Pin<&mut Self>,
+        self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &mut [u8],
     ) -> Poll<io::Result<usize>> {
-        let state = &mut *self.0.lock().unwrap();
+        let mut state_guard = self.0.lock().unwrap();
+        let state = &mut *state_guard;
 
         loop {
             match state {

src/io/stdout.rs

@@ -89,11 +89,12 @@ enum Operation {
 
 impl Write for Stdout {
     fn poll_write(
-        mut self: Pin<&mut Self>,
+        self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        let state = &mut *self.0.lock().unwrap();
+        let mut state_guard = self.0.lock().unwrap();
+        let state = &mut *state_guard;
 
         loop {
             match state {
@@ -137,8 +138,9 @@ impl Write for Stdout {
         }
     }
 
-    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        let state = &mut *self.0.lock().unwrap();
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let mut state_guard = self.0.lock().unwrap();
+        let state = &mut *state_guard;
 
         loop {
             match state {