Make Writer::flush a no-op default method

Closes #9126

Author: alexcrichton

src/librustuv/uvio.rs

@@ -1653,9 +1653,6 @@ impl RtioFileStream for UvFileStream {
         let self_ = unsafe { cast::transmute::<&UvFileStream, &mut UvFileStream>(self) };
         self_.seek_common(0, SEEK_CUR)
     }
-    fn flush(&mut self) -> Result<(), IoError> {
-        Ok(())
-    }
 }
 
 pub struct UvProcess {

src/libstd/rt/io/buffered.rs

@@ -418,7 +418,6 @@ mod test {
 
         impl rt::io::Writer for S {
             fn write(&mut self, _: &[u8]) {}
-            fn flush(&mut self) {}
         }
 
         impl rt::io::Reader for S {

src/libstd/rt/io/comm_adapters.rs

@@ -32,8 +32,6 @@ impl<C: GenericChan<~[u8]>> ChanWriter<C> {
 
 impl<C: GenericChan<~[u8]>> Writer for ChanWriter<C> {
     fn write(&mut self, _buf: &[u8]) { fail!() }
-
-    fn flush(&mut self) { fail!() }
 }
 
 struct ReaderPort<R>;

src/libstd/rt/io/file.rs

@@ -383,15 +383,6 @@ impl Writer for FileStream {
             }
         }
     }
-
-    fn flush(&mut self) {
-        match self.fd.flush() {
-            Ok(_) => (),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-            }
-        }
-    }
 }
 
 /// a `std::rt::io:Seek` trait impl for file I/O.

src/libstd/rt/io/mem.rs

@@ -62,8 +62,6 @@ impl Writer for MemWriter {
         // Bump us forward
         self.pos += buf.len();
     }
-
-    fn flush(&mut self) { /* no-op */ }
 }
 
 impl Seek for MemWriter {

src/libstd/rt/io/mock.rs

@@ -32,19 +32,16 @@ impl Reader for MockReader {
 
 pub struct MockWriter {
     priv write: ~fn(buf: &[u8]),
-    priv flush: ~fn()
 }
 
 impl MockWriter {
     pub fn new() -> MockWriter {
         MockWriter {
             write: |_| (),
-            flush: || ()
         }
     }
 }
 
 impl Writer for MockWriter {
     fn write(&mut self, buf: &[u8]) { (self.write)(buf) }
-    fn flush(&mut self) { (self.flush)() }
 }

src/libstd/rt/io/mod.rs

@@ -810,8 +810,12 @@ pub trait Writer {
     /// Raises the `io_error` condition on error
     fn write(&mut self, buf: &[u8]);
 
-    /// Flush output
-    fn flush(&mut self);
+    /// Flush this output stream, ensuring that all intermediately buffered
+    /// contents reach their destination.
+    ///
+    /// This is by default a no-op and implementors of the `Writer` trait should
+    /// decide whether their stream needs to be buffered or not.
+    fn flush(&mut self) {}
 
     /// Write the result of passing n through `int::to_str_bytes`.
     fn write_int(&mut self, n: int) {

src/libstd/rt/io/native/file.rs

@@ -132,8 +132,6 @@ impl Writer for FileDesc {
             raise_error();
         }
     }
-
-    fn flush(&mut self) {}
 }
 
 impl Drop for FileDesc {

src/libstd/rt/io/net/tcp.rs

@@ -84,8 +84,6 @@ impl Writer for TcpStream {
             Err(ioerr) => io_error::cond.raise(ioerr),
         }
     }
-
-    fn flush(&mut self) { /* no-op */ }
 }
 
 pub struct TcpListener {

src/libstd/rt/io/net/udp.rs

@@ -100,8 +100,6 @@ impl Writer for UdpStream {
             sock.sendto(buf, self.connectedTo);
         }
     }
-
-    fn flush(&mut self) { fail!() }
 }
 
 #[cfg(test)]

src/libstd/rt/io/net/unix.rs

@@ -78,7 +78,6 @@ impl Reader for UnixStream {
 
 impl Writer for UnixStream {
     fn write(&mut self, buf: &[u8]) { self.obj.write(buf) }
-    fn flush(&mut self) { self.obj.flush() }
 }
 
 pub struct UnixListener {

src/libstd/rt/io/pipe.rs

@@ -86,6 +86,4 @@ impl Writer for PipeStream {
             }
         }
     }
-
-    fn flush(&mut self) {}
 }

src/libstd/rt/io/stdio.rs

@@ -294,8 +294,6 @@ impl Writer for StdWriter {
             Err(e) => io_error::cond.raise(e)
         }
     }
-
-    fn flush(&mut self) { /* nothing to do */ }
 }
 
 #[cfg(test)]

src/libstd/rt/rtio.rs

@@ -173,7 +173,6 @@ pub trait RtioFileStream {
     fn pwrite(&mut self, buf: &[u8], offset: u64) -> Result<(), IoError>;
     fn seek(&mut self, pos: i64, whence: SeekStyle) -> Result<u64, IoError>;
     fn tell(&self) -> Result<u64, IoError>;
-    fn flush(&mut self) -> Result<(), IoError>;
 }
 
 pub trait RtioProcess {