chat: Move chatHead client var to clientVars hook

CHANGELOG.md

@@ -96,6 +96,7 @@
     * The `sendChatMessageToPadClients()` function in
       `src/node/handler/PadMessageHandler.js` is deprecated.
   * Client-side:
+    * The `chat` global variable is deprecated.
     * The `pad.determineChatVisibility()` method was removed.
     * The `pad.determineChatAndUsersVisibility()` method was removed.
 * Returning `true` from a `handleMessageSecurity` hook function is deprecated;

src/ep.json

@@ -21,6 +21,7 @@
         "postAceInit": "ep_etherpad-lite/static/js/chat"
       },
       "hooks": {
+        "clientVars": "ep_etherpad-lite/node/chat",
         "eejsBlock_mySettings": "ep_etherpad-lite/node/chat",
         "eejsBlock_stickyContainer": "ep_etherpad-lite/node/chat",
         "handleMessage": "ep_etherpad-lite/node/chat",

src/node/chat.js

@@ -23,6 +23,8 @@ const sendChatMessageToPadClients = async (message, padId) => {
   await promise;
 };
 
+exports.clientVars = (hookName, {pad: {chatHead}}) => ({chatHead});
+
 exports.eejsBlock_mySettings = (hookName, context) => {
   context.content += `
     <p class="hide-for-mobile">

src/node/handler/PadMessageHandler.js

@@ -903,9 +903,6 @@ const handleClientReady = async (socket, message) => {
       padShortcutEnabled: settings.padShortcutEnabled,
       initialTitle: `Pad: ${sessionInfo.auth.padID}`,
       opts: {},
-      // tell the client the number of the latest chat-message, which will be
-      // used to request the latest 100 chat-messages later (GET_CHAT_MESSAGES)
-      chatHead: pad.chatHead,
       numConnectedUsers: roomSockets.length,
       readOnlyId: sessionInfo.readOnlyPadId,
       readonly: sessionInfo.readonly,

src/templates/pad.html

@@ -467,9 +467,18 @@
 
       /* TODO: These globals shouldn't exist. */
       pad = require('ep_etherpad-lite/static/js/pad').pad;
-      chat = require('ep_etherpad-lite/static/js/chat').chat;
       padeditbar = require('ep_etherpad-lite/static/js/pad_editbar').padeditbar;
       padimpexp = require('ep_etherpad-lite/static/js/pad_impexp').padimpexp;
+
+      Object.defineProperty(window, 'chat', {
+        get: () => {
+          const {padutils: {warnDeprecated}} = require('ep_etherpad-lite/static/js/pad_utils');
+          warnDeprecated(
+              'window.chat is deprecated and will be removed in a future version of Etherpad');
+          return require('ep_etherpad-lite/static/js/chat').chat;
+        },
+      });
+
       require('ep_etherpad-lite/static/js/skin_variants');
 
     }());