clear composer undo history when sending a message

src/components/views/rooms/BasicMessageComposer.js

@@ -136,6 +136,10 @@ export default class BasicMessageEditor extends React.Component {
         return this._lastCaret;
     }
 
+    clearUndoHistory() {
+        this.historyManager.clear();
+    }
+
     getCaret() {
         return this._lastCaret;
     }

src/components/views/rooms/SendMessageComposer.js

@@ -100,6 +100,8 @@ export default class SendMessageComposer extends React.Component {
         const {roomId} = this.props.room;
         this.context.matrixClient.sendMessage(roomId, createMessageContent(this.model, this.props.permalinkCreator));
         this.model.reset([]);
+        this._editorRef.clearUndoHistory();
+
         if (isReply) {
             // Clear reply_to_event as we put the message into the queue
             // if the send fails, retry will handle resending.

src/editor/history.js

@@ -18,6 +18,10 @@ export const MAX_STEP_LENGTH = 10;
 
 export default class HistoryManager {
     constructor() {
+        this.clear();
+    }
+
+    clear() {
         this._stack = [];
         this._newlyTypedCharCount = 0;
         this._currentIndex = -1;