feat: switch input source during prefix mode (#434)

On macOS, opt-in under [experimental], temporarily switch the host input
source to the current ASCII-capable layout while prefix mode is active so
prefix commands register even when a CJK IME is composing, then restore the
previous input source when prefix mode exits or is cancelled. No-op when the
current source is already ASCII-capable, on non-macOS platforms, or when any
input source call fails. Pane text input is unaffected.

Also pin next_resize_poll in next_loop_deadline_includes_selection_autoscroll_deadline
so the selection autoscroll deadline stays the earliest; the default resize
poll could otherwise beat it and flake the assertion.

refs #400

Co-authored-by: Can Celik <ogulcancelik@gmail.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/src/platform/mod.rs b/src/platform/mod.rs
index a836ed81..12c275f0 100644
--- a/src/platform/mod.rs
+++ b/src/platform/mod.rs
@@ -96,6 +96,49 @@ mod fallback;
 #[cfg(not(any(target_os = "linux", target_os = "macos")))]
 pub use fallback::*;
 
+#[cfg(not(target_os = "macos"))]
+#[derive(Debug)]
+pub(crate) struct InputSourceRestore;
+
+#[cfg(not(target_os = "macos"))]
+pub(crate) fn switch_to_ascii_input_source() -> Option<InputSourceRestore> {
+    None
+}
+
+/// Switches the host keyboard input source while prefix mode is active.
+///
+/// `App` drives this through a trait so the prefix-mode transitions can be
+/// tested with a fake, without touching the real macOS APIs or leaking a
+/// platform-specific restore type into `App`.
+pub(crate) trait PrefixInputSource {
+    /// Switch to an ASCII-capable input source for prefix commands. No-op if
+    /// the current source is already ASCII-capable, the platform is
+    /// unsupported, or the switch fails. Calling it again before `restore`
+    /// keeps the source saved by the first call.
+    fn switch_to_ascii(&mut self);
+
+    /// Restore whatever `switch_to_ascii` saved. No-op if nothing was switched.
+    fn restore(&mut self);
+}
+
+/// Production [`PrefixInputSource`] backed by the per-platform API.
+#[derive(Default)]
+pub(crate) struct RealPrefixInputSource {
+    restore: Option<InputSourceRestore>,
+}
+
+impl PrefixInputSource for RealPrefixInputSource {
+    fn switch_to_ascii(&mut self) {
+        if self.restore.is_none() {
+            self.restore = switch_to_ascii_input_source();
+        }
+    }
+
+    fn restore(&mut self) {
+        let _ = self.restore.take();
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;