Add #[must_use] to conversions that move self

library/std/src/io/buffered/bufwriter.rs

@@ -476,6 +476,7 @@ pub struct WriterPanicked {
 impl WriterPanicked {
     /// Returns the perhaps-unwritten data.  Some of this data may have been written by the
     /// panicking call(s) to the underlying writer, so simply writing it again is not a good idea.
+    #[must_use = "`self` will be dropped if the result is not used"]
     #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
     pub fn into_inner(self) -> Vec<u8> {
         self.buf

library/std/src/io/error.rs

@@ -657,6 +657,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "io_error_inner", since = "1.3.0")]
+    #[must_use = "`self` will be dropped if the result is not used"]
     #[inline]
     pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
         match self.repr {

library/std/src/io/stdio.rs

@@ -464,6 +464,7 @@ impl Stdin {
     ///     println!("got a line: {}", line.unwrap());
     /// }
     /// ```
+    #[must_use = "`self` will be dropped if the result is not used"]
     #[unstable(feature = "stdin_forwarders", issue = "87096")]
     pub fn lines(self) -> Lines<StdinLock<'static>> {
         self.into_locked().lines()