rhg: handle broken pipe error for stderr

Differential Revision: https://phab.mercurial-scm.org/D8871

rust/rhg/src/ui.rs

@@ -1,96 +1,106 b''
 use std::io;
 use std::io::{ErrorKind, Write};
 
 #[derive(Debug)]
 pub struct Ui {
     stdout: std::io::Stdout,
     stderr: std::io::Stderr,
 }
 
 /// The kind of user interface error
 pub enum UiError {
     /// The standard output stream cannot be written to
     StdoutError(io::Error),
     /// The standard error stream cannot be written to
     StderrError(io::Error),
 }
 
 /// The commandline user interface
 impl Ui {
     pub fn new() -> Self {
         Ui {
             stdout: std::io::stdout(),
             stderr: std::io::stderr(),
         }
     }
 
     /// Returns a buffered handle on stdout for faster batch printing
     /// operations.
     pub fn stdout_buffer(&self) -> StdoutBuffer<std::io::StdoutLock> {
         StdoutBuffer::new(self.stdout.lock())
     }
 
     /// Write bytes to stdout
     pub fn write_stdout(&self, bytes: &[u8]) -> Result<(), UiError> {
         let mut stdout = self.stdout.lock();
 
         stdout
             .write_all(bytes)
             .or_else(|e| handle_stdout_error(e))?;
 
         stdout.flush().or_else(|e| handle_stdout_error(e))
     }
 
     /// Write bytes to stderr
     pub fn write_stderr(&self, bytes: &[u8]) -> Result<(), UiError> {
         let mut stderr = self.stderr.lock();
 
         stderr
             .write_all(bytes)
             .or_else(|e| handle_stderr_error(e))?;
 
-        stderr.flush().or_else(|e| Err(UiError::StderrError(e)))
+        stderr.flush().or_else(|e| handle_stderr_error(e))
     }
 }
 
 /// A buffered stdout writer for faster batch printing operations.
 pub struct StdoutBuffer<W: Write> {
     buf: io::BufWriter<W>,
 }
 
 impl<W: Write> StdoutBuffer<W> {
     pub fn new(writer: W) -> Self {
         let buf = io::BufWriter::new(writer);
         Self { buf }
     }
 
     /// Write bytes to stdout buffer
     pub fn write_all(&mut self, bytes: &[u8]) -> Result<(), UiError> {
         self.buf
             .write_all(bytes)
             .or_else(|e| handle_stdout_error(e))
     }
 
     /// Flush bytes to stdout
     pub fn flush(&mut self) -> Result<(), UiError> {
         self.buf.flush().or_else(|e| handle_stdout_error(e))
     }
 }
 
 /// Sometimes writing to stdout is not possible, try writing to stderr to
 /// signal that failure, otherwise just bail.
 fn handle_stdout_error(error: io::Error) -> Result<(), UiError> {
     if let ErrorKind::BrokenPipe = error.kind() {
         // This makes `| head` work for example
         return Ok(());
     }
     let mut stderr = io::stderr();
 
     stderr
         .write_all(&[b"abort: ", error.to_string().as_bytes(), b"\n"].concat())
         .map_err(|e| UiError::StderrError(e))?;
 
     stderr.flush().map_err(|e| UiError::StderrError(e))?;
 
     Err(UiError::StdoutError(error))
 }
+
+/// Sometimes writing to stderr is not possible.
+fn handle_stderr_error(error: io::Error) -> Result<(), UiError> {
+    // A broken pipe should not result in a error
+    // like with `| head` for example
+    if let ErrorKind::BrokenPipe = error.kind() {
+        return Ok(());
+    }
+    Err(UiError::StdoutError(error))
+}