Fix dismissing edit composer when change was undone (#9109)

* Fix dismissing edit composer when change was undone

* Add tests

cypress/e2e/editing/editing.spec.ts

@@ -0,0 +1,70 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/// <reference types="cypress" />
+
+import { MessageEvent } from "matrix-events-sdk";
+
+import type { ISendEventResponse } from "matrix-js-sdk/src/@types/requests";
+import type { EventType } from "matrix-js-sdk/src/@types/event";
+import { SynapseInstance } from "../../plugins/synapsedocker";
+import Chainable = Cypress.Chainable;
+
+const sendEvent = (roomId: string): Chainable<ISendEventResponse> => {
+    return cy.sendEvent(
+        roomId,
+        null,
+        "m.room.message" as EventType,
+        MessageEvent.from("Message").serialize().content,
+    );
+};
+
+describe("Editing", () => {
+    let synapse: SynapseInstance;
+
+    beforeEach(() => {
+        cy.startSynapse("default").then(data => {
+            synapse = data;
+            cy.initTestUser(synapse, "Edith").then(() => {
+                cy.injectAxe();
+                return cy.createRoom({ name: "Test room" }).as("roomId");
+            });
+        });
+    });
+
+    afterEach(() => {
+        cy.stopSynapse(synapse);
+    });
+
+    it("should close the composer when clicking save after making a change and undoing it", () => {
+        cy.get<string>("@roomId").then(roomId => {
+            sendEvent(roomId);
+            cy.visit("/#/room/" + roomId);
+        });
+
+        // Edit message
+        cy.contains(".mx_RoomView_body .mx_EventTile .mx_EventTile_line", "Message").within(() => {
+            cy.get('[aria-label="Edit"]').click({ force: true }); // Cypress has no ability to hover
+            cy.checkA11y();
+            cy.get(".mx_BasicMessageComposer_input").type("Foo{backspace}{backspace}{backspace}{enter}");
+            cy.checkA11y();
+        });
+        cy.get(".mx_RoomView_body .mx_EventTile").contains(".mx_EventTile[data-scroll-tokens]", "Message");
+
+        // Assert that the edit composer has gone away
+        cy.get(".mx_EditMessageComposer").should("not.exist");
+    });
+});