PLT-3785 Re-enabled marking messages unread (#4179)

* Re-added ALT+Click to mark msgs unread, fixed mentions for DM

* Added string to /shortcuts

webapp/actions/post_actions.jsx

@@ -73,6 +73,7 @@ export function setUnreadPost(channelId, postId) {
     let ownNewMessage = false;
     const post = PostStore.getPost(channelId, postId);
     const posts = PostStore.getVisiblePosts(channelId).posts;
+    const currentChannel = ChannelStore.getCurrent();
     var currentUsedId = UserStore.getCurrentId();
     if (currentUsedId === post.user_id || PostUtils.isSystemMessage(post)) {
         for (const otherPostId in posts) {
@@ -103,6 +104,12 @@ export function setUnreadPost(channelId, postId) {
                 unreadPosts += 1;
             }
         }
+
+        // Temporary workaround for DM channels having wrong unread values
+        if (currentChannel.type === Constants.DM_CHANNEL) {
+            unreadPosts = 0;
+        }
+
         const member = ChannelStore.getMember(channelId);
         const channel = ChannelStore.get(channelId);
         member.last_viewed_at = lastViewed;

webapp/components/post_view/components/post.jsx

@@ -4,6 +4,7 @@
 import PostHeader from './post_header.jsx';
 import PostBody from './post_body.jsx';
 import ProfilePicture from 'components/profile_picture.jsx';
+import * as PostActions from 'actions/post_actions.jsx';
 
 import Constants from 'utils/constants.jsx';
 const ActionTypes = Constants.ActionTypes;
@@ -49,13 +50,11 @@ export default class Post extends React.Component {
         this.refs.info.forceUpdate();
         this.refs.header.forceUpdate();
     }
-    handlePostClick() {
-        /* Disabled do to a bug: https://mattermost.atlassian.net/browse/PLT-3785
+    handlePostClick(e) {
         if (e.altKey) {
             e.preventDefault();
             PostActions.setUnreadPost(this.props.post.channel_id, this.props.post.id);
         }
-        */
     }
     shouldComponentUpdate(nextProps, nextState) {
         if (!Utils.areObjectsEqual(nextProps.post, this.props.post)) {

webapp/stores/channel_store.jsx

@@ -328,8 +328,9 @@ class ChannelStoreClass extends EventEmitter {
         let chMentionCount = chMember.mention_count;
         let chUnreadCount = ch.total_msg_count - chMember.msg_count;
 
+        // Temporary workaround for DM channels having wrong unread values
         if (ch.type === 'D') {
-            chMentionCount = chUnreadCount;
+            chMentionCount = 0;
         } else if (chMember.notify_props && chMember.notify_props.mark_unread === NotificationPrefs.MENTION) {
             chUnreadCount = 0;
         }