FIX: Allow only groups with flairs to be selected (#13744)

It used the same permission check as for primary groups which is
wrong because not all groups that can be primary have a flair.

app/services/user_updater.rb

@@ -124,7 +124,7 @@ class UserUpdater
     if attributes[:flair_group_id] &&
       attributes[:flair_group_id] != user.flair_group_id &&
       (attributes[:flair_group_id].blank? ||
-        guardian.can_use_primary_group?(user, attributes[:flair_group_id]))
+        guardian.can_use_flair_group?(user, attributes[:flair_group_id]))
 
       user.flair_group_id = attributes[:flair_group_id]
     end

lib/guardian.rb

@@ -323,6 +323,12 @@ class Guardian
     (group ? !group.automatic : false)
   end
 
+  def can_use_flair_group?(user, group_id = nil)
+    return false if !user || !group_id || !user.group_ids.include?(group_id.to_i)
+    flair_icon, flair_upload_id = Group.where(id: group_id.to_i).pluck_first(:flair_icon, :flair_upload_id)
+    flair_icon.present? || flair_upload_id.present?
+  end
+
   def can_change_primary_group?(user)
     user && is_staff?
   end

spec/components/guardian_spec.rb

@@ -2692,6 +2692,33 @@ describe Guardian do
     end
   end
 
+  describe 'can_use_flair_group?' do
+    fab!(:group) { Fabricate(:group, title: 'Groupie', flair_icon: 'icon') }
+
+    it 'is false without a logged in user' do
+      expect(Guardian.new(nil).can_use_flair_group?(user)).to eq(false)
+    end
+
+    it 'is false if the group does not exist' do
+      expect(Guardian.new(user).can_use_flair_group?(user, nil)).to eq(false)
+      expect(Guardian.new(user).can_use_flair_group?(user, Group.last.id + 1)).to eq(false)
+    end
+
+    it 'is false if the user is not a part of the group' do
+      expect(Guardian.new(user).can_use_flair_group?(user, group.id)).to eq(false)
+    end
+
+    it 'is false if the group does not have a flair' do
+      group.update(flair_icon: nil)
+      expect(Guardian.new(user).can_use_flair_group?(user, group.id)).to eq(false)
+    end
+
+    it 'is true if the user is a part of the group and the group has a flair' do
+      user.update(groups: [group])
+      expect(Guardian.new(user).can_use_flair_group?(user, group.id)).to eq(true)
+    end
+  end
+
   describe 'can_change_trust_level?' do
 
     it 'is false without a logged in user' do