pass failing test case for 'dw'. When we delete to the end of the file and the position the cursor was previously at no longer exists, move cursor to last valid character in file.

fcore/normal-mode/make-normal-delete.sml

@@ -277,7 +277,32 @@ struct
       val initialMsg = Fn.initMsgs (low, length, buffer)
       val buffer = LineGap.delete (low, length, buffer)
     in
-      finishAfterDeletingBuffer (app, low, buffer, time, initialMsg)
+      if low >= #textLength buffer - 1 andalso #textLength buffer > 0 then
+        (* edge case:
+         * when we delete from the cursor's position to the end of a file,
+         * we have to move the cursor to be on the last char
+         * because the original cursor's position is no longer valid. *)
+        let
+          val newCursorIdx = Int.max (#textLength buffer - 1, 0)
+          val buffer = LineGap.goToIdx (newCursorIdx, buffer)
+          val newCursorIdx =
+            if Cursor.isOnNewlineAfterChr (buffer, newCursorIdx) then
+              newCursorIdx - 1
+            else
+              newCursorIdx
+        in
+          finishAfterDeletingBuffer
+            (app, newCursorIdx, buffer, time, initialMsg)
+        end
+      else
+        let
+          val buffer = LineGap.goToIdx (low, buffer)
+          val newCursorIdx =
+            if Cursor.isOnNewlineAfterChr (buffer, low) then low - 1 else low
+        in
+          finishAfterDeletingBuffer
+            (app, newCursorIdx, buffer, time, initialMsg)
+        end
     end
 
   fun deleteByDfa (app as {buffer, ...}: app_type, count, fMove, time) =