discard stale completion requests

Completion requests are computed asynchronously to avoid common micro
freezes while editing. This means that once a completion request
completes, the state of the editor might have changed. Currently,
there is a check to ensure we are still in insert mode. However,
we also need to ensure that the view and document hasn't changed
to avoid accidentally using a savepoint with the wrong view/document.

Furthermore, the editor might request a new completion while the
previous completion request hasn't complemented yet. This can
lead to weird flickering or an outdated completion request replacing
a newer completion that has already completed (the LSP server
is not required to process completion requests in order). This change
also needed to ensure determinism/linear ordering so that completion
popup always correspond to the last completion request.

1 files changed, 10 insertions, 1 deletions

diff --git a/helix-view/src/editor.rs b/helix-view/src/editor.rs
index 5b819b33..c6541105 100644
--- a/helix-view/src/editor.rs
+++ b/helix-view/src/editor.rs
@@ -31,7 +31,7 @@ use std::{
 use tokio::{
     sync::{
         mpsc::{unbounded_channel, UnboundedReceiver, UnboundedSender},
-        Notify, RwLock,
+        oneshot, Notify, RwLock,
     },
     time::{sleep, Duration, Instant, Sleep},
 };
@@ -852,6 +852,14 @@ pub struct Editor {
     /// avoid calculating the cursor position multiple
     /// times during rendering and should not be set by other functions.
     pub cursor_cache: Cell<Option<Option<Position>>>,
+    /// When a new completion request is sent to the server old
+    /// unifinished request must be dropped. Each completion
+    /// request is associated with a channel that cancels
+    /// when the channel is dropped. That channel is stored
+    /// here. When a new completion request is sent this
+    /// field is set and any old requests are automatically
+    /// canceled as a result
+    pub completion_request_handle: Option<oneshot::Sender<()>>,
 }
 
 pub type RedrawHandle = (Arc<Notify>, Arc<RwLock<()>>);
@@ -950,6 +958,7 @@ impl Editor {
             redraw_handle: Default::default(),
             needs_redraw: false,
             cursor_cache: Cell::new(None),
+            completion_request_handle: None,
         }
     }