Add must_use annotations to Result::is_ok and is_err

src/libcore/option.rs

@@ -178,6 +178,7 @@ impl<T> Option<T> {
     /// ```
     ///
     /// [`Some`]: #variant.Some
+    #[must_use]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_some(&self) -> bool {
@@ -200,6 +201,7 @@ impl<T> Option<T> {
     /// ```
     ///
     /// [`None`]: #variant.None
+    #[must_use]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_none(&self) -> bool {

src/libcore/result.rs

@@ -277,6 +277,7 @@ impl<T, E> Result<T, E> {
     /// let x: Result<i32, &str> = Err("Some error message");
     /// assert_eq!(x.is_ok(), false);
     /// ```
+    #[must_use]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_ok(&self) -> bool {
@@ -301,6 +302,7 @@ impl<T, E> Result<T, E> {
     /// let x: Result<i32, &str> = Err("Some error message");
     /// assert_eq!(x.is_err(), true);
     /// ```
+    #[must_use]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_err(&self) -> bool {

src/librustc_data_structures/owning_ref/mod.rs

@@ -1471,7 +1471,7 @@ mod tests {
             let x = Box::new(123_i32);
             let y: Box<dyn Any> = x;
 
-            OwningRef::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_ok();
+            assert!(OwningRef::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_ok());
         }
 
         #[test]
@@ -1481,7 +1481,7 @@ mod tests {
             let x = Box::new(123_i32);
             let y: Box<dyn Any> = x;
 
-            OwningRef::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_err();
+            assert!(!OwningRef::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_err());
         }
     }
 
@@ -1868,7 +1868,7 @@ mod tests {
             let x = Box::new(123_i32);
             let y: Box<dyn Any> = x;
 
-            OwningRefMut::new(y).try_map_mut(|x| x.downcast_mut::<i32>().ok_or(())).is_ok();
+            assert!(OwningRefMut::new(y).try_map_mut(|x| x.downcast_mut::<i32>().ok_or(())).is_ok());
         }
 
         #[test]
@@ -1878,7 +1878,7 @@ mod tests {
             let x = Box::new(123_i32);
             let y: Box<dyn Any> = x;
 
-            OwningRefMut::new(y).try_map_mut(|x| x.downcast_mut::<i32>().ok_or(())).is_err();
+            assert!(!OwningRefMut::new(y).try_map_mut(|x| x.downcast_mut::<i32>().ok_or(())).is_err());
         }
 
         #[test]
@@ -1888,7 +1888,7 @@ mod tests {
             let x = Box::new(123_i32);
             let y: Box<dyn Any> = x;
 
-            OwningRefMut::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_ok();
+            assert!(OwningRefMut::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_ok());
         }
 
         #[test]
@@ -1898,7 +1898,7 @@ mod tests {
             let x = Box::new(123_i32);
             let y: Box<dyn Any> = x;
 
-            OwningRefMut::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_err();
+            assert!(!OwningRefMut::new(y).try_map(|x| x.downcast_ref::<i32>().ok_or(())).is_err());
         }
 
         #[test]

src/libstd/sync/mpsc/mod.rs

@@ -1005,7 +1005,7 @@ impl<T> SyncSender<T> {
     /// thread::spawn(move || {
     ///     // This will return an error and send
     ///     // no message if the buffer is full
-    ///     sync_sender2.try_send(3).is_err();
+    ///     let _ = sync_sender2.try_send(3);
     /// });
     ///
     /// let mut msg;

src/test/run-pass/issues/issue-18353.rs

@@ -11,5 +11,5 @@ struct Str {
 
 fn main() {
     let str: Option<&Str> = None;
-    str.is_some();
+    let _ = str.is_some();
 }