chore: use #[non_exhaustive] instead of private unit field (#3320)

tokio-util/src/codec/bytes_codec.rs

@@ -42,12 +42,13 @@ use std::io;
 /// ```
 ///
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Default)]
-pub struct BytesCodec(());
+#[non_exhaustive]
+pub struct BytesCodec;
 
 impl BytesCodec {
     /// Creates a new `BytesCodec` for shipping around raw bytes.
     pub fn new() -> BytesCodec {
-        BytesCodec(())
+        BytesCodec
     }
 }
 

tokio-util/src/codec/framed.rs

@@ -219,7 +219,6 @@ impl<T, U> Framed<T, U> {
             codec: self.inner.codec,
             read_buf: self.inner.state.read.buffer,
             write_buf: self.inner.state.write.buffer,
-            _priv: (),
         }
     }
 }
@@ -282,7 +281,7 @@ where
 ///
 /// [`Framed`]: crate::codec::Framed
 #[derive(Debug)]
-#[allow(clippy::manual_non_exhaustive)]
+#[non_exhaustive]
 pub struct FramedParts<T, U> {
     /// The inner transport used to read bytes to and write bytes to
     pub io: T,
@@ -295,10 +294,6 @@ pub struct FramedParts<T, U> {
 
     /// A buffer with unprocessed data which are not written yet.
     pub write_buf: BytesMut,
-
-    /// This private field allows us to add additional fields in the future in a
-    /// backwards compatible way.
-    _priv: (),
 }
 
 impl<T, U> FramedParts<T, U> {
@@ -312,7 +307,6 @@ impl<T, U> FramedParts<T, U> {
             codec,
             read_buf: BytesMut::new(),
             write_buf: BytesMut::new(),
-            _priv: (),
         }
     }
 }

tokio-util/src/codec/length_delimited.rs

@@ -409,9 +409,8 @@ pub struct Builder {
 }
 
 /// An error when the number of bytes read is more than max frame length.
-pub struct LengthDelimitedCodecError {
-    _priv: (),
-}
+#[non_exhaustive]
+pub struct LengthDelimitedCodecError;
 
 /// A codec for frames delimited by a frame head specifying their lengths.
 ///
@@ -496,7 +495,7 @@ impl LengthDelimitedCodec {
             if n > self.builder.max_frame_len as u64 {
                 return Err(io::Error::new(
                     io::ErrorKind::InvalidData,
-                    LengthDelimitedCodecError { _priv: () },
+                    LengthDelimitedCodecError,
                 ));
             }
 
@@ -586,7 +585,7 @@ impl Encoder<Bytes> for LengthDelimitedCodec {
         if n > self.builder.max_frame_len {
             return Err(io::Error::new(
                 io::ErrorKind::InvalidInput,
-                LengthDelimitedCodecError { _priv: () },
+                LengthDelimitedCodecError,
             ));
         }