fix: rewrite prefix after carriage return

crates/turborepo-ui/src/prefixed.rs

@@ -128,12 +128,19 @@ impl<W: Write> PrefixedWriter<W> {
 
 impl<W: Write> Write for PrefixedWriter<W> {
     fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
-        self.writer.write_all(self.prefix.as_bytes())?;
-
+        for chunk in buf.split_inclusive(|c| *c == b'\r') {
+            // Before we write the chunk we write the prefix as either:
+            // - this is the first iteration and we haven't written the prefix
+            // - the previous chunk ended with a \r and the cursor is currently as the start
+            //   of the line so we want to rewrite the prefix over the existing prefix in
+            //   the line
+            self.writer.write_all(self.prefix.as_bytes())?;
+            self.writer.write_all(chunk)?;
+        }
         // We do end up writing more bytes than this to the underlying writer, but we
         // cannot report this to the callers as the amount of bytes we report
         // written must be less than or equal to the number of bytes in the buffer.
-        self.writer.write(buf)
+        Ok(buf.len())
     }
 
     fn flush(&mut self) -> std::io::Result<()> {
@@ -192,4 +199,20 @@ mod test {
         writer.write_all(b"cool!").unwrap();
         assert_eq!(String::from_utf8(buffer).unwrap(), expected);
     }
+
+    #[test_case("\ra whole message \n", "turbo > \rturbo > a whole message \n" ; "basic prefix cr")]
+    #[test_case("no return", "turbo > no return" ; "no return")]
+    #[test_case("foo\rbar\rbaz", "turbo > foo\rturbo > bar\rturbo > baz" ; "multiple crs")]
+    #[test_case("foo\r", "turbo > foo\r" ; "trailing cr")]
+    fn test_prefixed_writer_cr(input: &str, expected: &str) {
+        let mut buffer = Vec::new();
+        let mut writer = PrefixedWriter::new(
+            UI::new(false),
+            Style::new().apply_to("turbo > "),
+            &mut buffer,
+        );
+
+        writer.write_all(input.as_bytes()).unwrap();
+        assert_eq!(String::from_utf8(buffer).unwrap(), expected);
+    }
 }