Fix error when viewing source of redacted events (#9914)

* Fix viewing source of redacted events

Clicking 'View Source' in the context menu of a redacted event causes an error,
and the user gets no visible result.

This fixes <ViewSource /> to indicate that the source is unavailable when a
message has been redacted. The original source remains available.

<SyntaxHighlight /> requires a non-null string for its `content` prop, and, in
the case of redacted events, <ViewSource /> was passing `undefined`. This is
ultimately because redacting an event causes `MatrixEvent.clearEvent` to be
`undefined`, which <ViewSource /> wasn't checking.

Fixes https://github.com/vector-im/element-web/issues/24165

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

* Use correct highlight.js call

Previous call signature was deprecated.

See https://github.com/highlightjs/highlight.js/issues/2277

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

test/components/structures/ViewSource-test.tsx

@@ -0,0 +1,59 @@
+/*
+Copyright 2023 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.
+*/
+
+import { render } from "@testing-library/react";
+import { EventType, MatrixEvent } from "matrix-js-sdk/src/matrix";
+import React from "react";
+
+import ViewSource from "../../../src/components/structures/ViewSource";
+import { mkEvent, stubClient } from "../../test-utils/test-utils";
+
+describe("ThreadView", () => {
+    const ROOM_ID = "!roomId:example.org";
+    const SENDER = "@alice:example.org";
+
+    let messageEvent: MatrixEvent;
+
+    const redactionEvent = mkEvent({
+        user: SENDER,
+        event: true,
+        type: EventType.RoomRedaction,
+        content: {},
+    });
+
+    beforeEach(() => {
+        messageEvent = new MatrixEvent({
+            type: EventType.RoomMessageEncrypted,
+            room_id: ROOM_ID,
+            sender: SENDER,
+            content: {},
+            state_key: undefined,
+        });
+        messageEvent.makeRedacted(redactionEvent);
+    });
+
+    beforeEach(stubClient);
+
+    // See https://github.com/vector-im/element-web/issues/24165
+    it("doesn't error when viewing redacted encrypted messages", () => {
+        // Sanity checks
+        expect(messageEvent.isEncrypted()).toBeTruthy();
+        // @ts-ignore clearEvent is private, but it's being used directly <ViewSource />
+        expect(messageEvent.clearEvent).toBe(undefined);
+
+        expect(() => render(<ViewSource mxEvent={messageEvent} onFinished={() => {}} />)).not.toThrow();
+    });
+});