fix(termion): Add workaround for failing cursor detection

src/backend/termion.rs

@@ -67,6 +67,7 @@ where
     W: Write,
 {
     writer: W,
+    cursor: Option<(u16, u16)>,
 }
 
 impl<W> TermionBackend<W>
@@ -83,7 +84,10 @@ where
     /// let backend = TermionBackend::new(stdout());
     /// ```
     pub const fn new(writer: W) -> Self {
-        Self { writer }
+        Self {
+            writer,
+            cursor: None,
+        }
     }
 }
 
@@ -137,11 +141,21 @@ where
     }
 
     fn get_cursor(&mut self) -> io::Result<(u16, u16)> {
-        termion::cursor::DetectCursorPos::cursor_pos(&mut self.writer).map(|(x, y)| (x - 1, y - 1))
+        match termion::cursor::DetectCursorPos::cursor_pos(&mut self.writer) {
+            Ok((x, y)) => {
+                let cursor = (x - 1, y - 1);
+                self.cursor = Some(cursor);
+                Ok(cursor)
+            }
+            Err(_) => self
+                .cursor
+                .ok_or_else(|| io::Error::other("No last known cursor position")),
+        }
     }
 
     fn set_cursor(&mut self, x: u16, y: u16) -> io::Result<()> {
         write!(self.writer, "{}", termion::cursor::Goto(x + 1, y + 1))?;
+        self.cursor = Some((x, y));
         self.writer.flush()
     }
 

tests/backend_termion.rs

@@ -61,3 +61,58 @@ fn backend_termion_should_only_write_diffs() -> Result<(), Box<dyn std::error::E
 
     Ok(())
 }
+
+/// Retrieving the cursor from an in-memory buffer will fail in
+/// `termion::cursor::DetectCursorPos::cursor_pos()`. If there is no known last cursor, retrieving
+/// the cursor will ulimately fail.
+///
+/// This simulates a usage of `termion` where retrieving the cursor fails in a multi-threaded
+/// environment: [](https://gitlab.redox-os.org/redox-os/termion/-/issues/173)
+#[cfg(feature = "termion")]
+#[test]
+fn backend_termion_should_fail_on_missing_last_known_cursor(
+) -> Result<(), Box<dyn std::error::Error>> {
+    use std::io::{self, Cursor};
+
+    use ratatui::{backend::TermionBackend, Terminal};
+
+    let mut bytes = Vec::new();
+    let mut stdout = Cursor::new(&mut bytes);
+
+    let backend = TermionBackend::new(&mut stdout);
+    let mut terminal = Terminal::new(backend)?;
+
+    let cursor = terminal.get_cursor();
+    let error_kind = cursor.unwrap_err().kind();
+    let expected_kind = io::ErrorKind::Other;
+
+    assert_eq!(error_kind, expected_kind);
+
+    Ok(())
+}
+
+/// Retrieving the cursor from an in-memory buffer will fail in
+/// `termion::cursor::DetectCursorPos::cursor_pos()`. If a cursor was set explicitely, retrieving
+/// the cursor will fallback to its last known position.
+///
+/// This simulates a usage of `termion` where retrieving the cursor fails in a multi-threaded
+/// environment: [](https://gitlab.redox-os.org/redox-os/termion/-/issues/173)
+#[cfg(feature = "termion")]
+#[test]
+fn backend_termion_should_use_last_known_cursor() -> Result<(), Box<dyn std::error::Error>> {
+    use std::io::Cursor;
+
+    use ratatui::{backend::TermionBackend, Terminal};
+
+    let mut bytes = Vec::new();
+    let mut stdout = Cursor::new(&mut bytes);
+
+    let backend = TermionBackend::new(&mut stdout);
+    let mut terminal = Terminal::new(backend)?;
+
+    terminal.set_cursor(13, 12)?;
+
+    assert_eq!(terminal.get_cursor()?, (13, 12));
+
+    Ok(())
+}