Add #[must_use] to remaining std functions (A-N)

4 files changed, 14 insertions, 0 deletions

diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs
index 59a9cd781cb..3da28695b34 100644
--- a/library/std/src/io/error.rs
+++ b/library/std/src/io/error.rs
@@ -442,6 +442,7 @@ impl Error {
     /// println!("last OS error: {:?}", Error::last_os_error());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub fn last_os_error() -> Error {
         Error::from_raw_os_error(sys::os::errno() as i32)
@@ -509,6 +510,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub fn raw_os_error(&self) -> Option<i32> {
         match self.repr {
@@ -547,6 +549,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "io_error_inner", since = "1.3.0")]
+    #[must_use]
     #[inline]
     pub fn get_ref(&self) -> Option<&(dyn error::Error + Send + Sync + 'static)> {
         match self.repr {
@@ -620,6 +623,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "io_error_inner", since = "1.3.0")]
+    #[must_use]
     #[inline]
     pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error + Send + Sync + 'static)> {
         match self.repr {
@@ -688,6 +692,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub fn kind(&self) -> ErrorKind {
         match self.repr {
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index abe29ba0f7c..f421185c2c5 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -1310,6 +1310,7 @@ pub struct Initializer(bool);
 impl Initializer {
     /// Returns a new `Initializer` which will zero out buffers.
     #[unstable(feature = "read_initializer", issue = "42788")]
+    #[must_use]
     #[inline]
     pub fn zeroing() -> Initializer {
         Initializer(true)
@@ -1324,6 +1325,7 @@ impl Initializer {
     /// the method accurately reflects the number of bytes that have been
     /// written to the head of the buffer.
     #[unstable(feature = "read_initializer", issue = "42788")]
+    #[must_use]
     #[inline]
     pub unsafe fn nop() -> Initializer {
         Initializer(false)
@@ -1331,6 +1333,7 @@ impl Initializer {
 
     /// Indicates if a buffer should be initialized.
     #[unstable(feature = "read_initializer", issue = "42788")]
+    #[must_use]
     #[inline]
     pub fn should_initialize(&self) -> bool {
         self.0
diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs
index 9389501e012..f471693774c 100644
--- a/library/std/src/io/stdio.rs
+++ b/library/std/src/io/stdio.rs
@@ -301,6 +301,7 @@ pub struct StdinLock<'a> {
 ///     Ok(())
 /// }
 /// ```
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn stdin() -> Stdin {
     static INSTANCE: SyncOnceCell<Mutex<BufReader<StdinRaw>>> = SyncOnceCell::new();
@@ -673,6 +674,7 @@ static STDOUT: SyncOnceCell<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>> = Sy
 ///     Ok(())
 /// }
 /// ```
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn stdout() -> Stdout {
     Stdout {
@@ -953,6 +955,7 @@ pub struct StderrLock<'a> {
 ///     Ok(())
 /// }
 /// ```
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn stderr() -> Stderr {
     // Note that unlike `stdout()` we don't use `at_exit` here to register a
diff --git a/library/std/src/io/util.rs b/library/std/src/io/util.rs
index 2f3520ae7a5..9cd7c514849 100644
--- a/library/std/src/io/util.rs
+++ b/library/std/src/io/util.rs
@@ -32,6 +32,7 @@ pub struct Empty;
 /// io::empty().read_to_string(&mut buffer).unwrap();
 /// assert!(buffer.is_empty());
 /// ```
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
 pub const fn empty() -> Empty {
@@ -112,6 +113,7 @@ pub struct Repeat {
 /// io::repeat(0b101).read_exact(&mut buffer).unwrap();
 /// assert_eq!(buffer, [0b101, 0b101, 0b101]);
 /// ```
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
 pub const fn repeat(byte: u8) -> Repeat {
@@ -192,6 +194,7 @@ pub struct Sink;
 /// let num_bytes = io::sink().write(&buffer).unwrap();
 /// assert_eq!(num_bytes, 5);
 /// ```
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
 pub const fn sink() -> Sink {