FIX: users watching tags in open tag groups not notified (#16384)

All users are members of the EVERYONE group, but this group is special and
is omitted from the group_users table. When checking permission we need to
make sure we also add a bypass.

This also fixes a very buggy test in post_alerter, it was confirming the
broken behavior due to fabricator flow.

When it defined the tag group the everyone group automatically had full access
then the additional permission fabricated just added one more group. After
fix was made to code the test started failing. Fabricators can be risky.

app/services/post_alerter.rb

@@ -802,7 +802,12 @@ class PostAlerter
      LEFT JOIN tag_group_memberships tgm ON tag_users.tag_id = tgm.tag_id
      LEFT JOIN tag_group_permissions tgp ON tgm.tag_group_id = tgp.tag_group_id
      LEFT JOIN group_users gu ON gu.user_id = tag_users.user_id
-         WHERE (tgp.group_id IS NULL OR tgp.group_id = gu.group_id OR gu.group_id = :staff_group_id)
+         WHERE (
+            tgp.group_id IS NULL OR
+            tgp.group_id = gu.group_id OR
+            tgp.group_id = :everyone_group_id OR
+            gu.group_id = :staff_group_id
+          )
                AND (tag_users.notification_level = :watching
                     AND tag_users.tag_id IN (:tag_ids)
                     AND (tu.user_id IS NULL OR tu.notification_level = :watching))
@@ -814,7 +819,8 @@ class PostAlerter
       topic_id: post.topic_id,
       category_id: post.topic.category_id,
       tag_ids: tag_ids,
-      staff_group_id: Group::AUTO_GROUPS[:staff]
+      staff_group_id: Group::AUTO_GROUPS[:staff],
+      everyone_group_id: Group::AUTO_GROUPS[:everyone]
     )
 
     if group_ids.present?

spec/models/tag_user_spec.rb

@@ -183,6 +183,11 @@ describe TagUser do
 
       it "sets notification levels correctly" do
 
+        # define a wide open tag group to ensure it also works
+        group = TagGroup.new(name: 'Visible & usable by everyone', tag_names: [watched_tag.name])
+        group.permissions = [[Group::AUTO_GROUPS[:everyone], TagGroupPermission.permission_types[:full]]]
+        group.save!
+
         expect(Notification.where(user_id: user.id, topic_id: watched_post.topic_id).count).to eq 1
         expect(Notification.where(user_id: user.id, topic_id: tracked_post.topic_id).count).to eq 0
 

spec/services/post_alerter_spec.rb

@@ -1372,8 +1372,10 @@ describe PostAlerter do
         tag = Fabricate(:tag)
         topic = Fabricate(:topic, tags: [tag])
         post = Fabricate(:post, topic: topic)
-        tag_group = Fabricate(:tag_group, tags: [tag])
-        Fabricate(:tag_group_permission, tag_group: tag_group, group: group)
+
+        tag_group = TagGroup.new(name: 'Only visible to group', tag_names: [tag.name])
+        tag_group.permissions = [[group.id, TagGroupPermission.permission_types[:full]]]
+        tag_group.save!
 
         TagUser.change(user.id, tag.id, TagUser.notification_levels[:watching])