ensure correct trigger/start completion offset

When re requesting a completion that already has a selected item we
reuse that selections savepoint. However, the selection has likely
changed since that savepoint which requires us to use the selection
from that savepoint

helix-term/src/commands.rs

@@ -4210,16 +4210,23 @@ pub fn completion(cx: &mut Context) {
 
     let (view, doc) = current!(cx.editor);
 
+    let savepoint = if let Some(CompleteAction::Selected { savepoint }) = &cx.editor.last_completion
+    {
+        savepoint.clone()
+    } else {
+        doc.savepoint(view)
+    };
+
     let language_server = match doc.language_server() {
         Some(language_server) => language_server,
         None => return,
     };
 
     let offset_encoding = language_server.offset_encoding();
-    let text = doc.text().slice(..);
-    let cursor = doc.selection(view.id).primary().cursor(text);
+    let text = savepoint.text.clone();
+    let cursor = savepoint.cursor();
 
-    let pos = pos_to_lsp_pos(doc.text(), cursor, offset_encoding);
+    let pos = pos_to_lsp_pos(&text, cursor, offset_encoding);
 
     let future = match language_server.completion(doc.identifier(), pos, None) {
         Some(future) => future,
@@ -4254,12 +4261,6 @@ pub fn completion(cx: &mut Context) {
     iter.reverse();
     let offset = iter.take_while(|ch| chars::char_is_word(*ch)).count();
     let start_offset = cursor.saturating_sub(offset);
-    let savepoint = if let Some(CompleteAction::Selected { savepoint }) = &cx.editor.last_completion
-    {
-        savepoint.clone()
-    } else {
-        doc.savepoint(view)
-    };
 
     let trigger_doc = doc.id();
     let trigger_view = view.id;

helix-view/src/document.rs

@@ -114,6 +114,19 @@ pub struct SavePoint {
     /// The view this savepoint is associated with
     pub view: ViewId,
     revert: Mutex<Transaction>,
+    pub text: Rope,
+}
+
+impl SavePoint {
+    pub fn cursor(&self) -> usize {
+        // we always create transactions with selections
+        self.revert
+            .lock()
+            .selection()
+            .unwrap()
+            .primary()
+            .cursor(self.text.slice(..))
+    }
 }
 
 pub struct Document {
@@ -1230,6 +1243,7 @@ impl Document {
         let savepoint = Arc::new(SavePoint {
             view: view.id,
             revert: Mutex::new(revert),
+            text: self.text.clone(),
         });
         self.savepoints.push(Arc::downgrade(&savepoint));
         savepoint