FIX: Enforce tag group count validation before sending to review queue (#12728)

There is a category setting that enforces 1 or more tags must be added to a topic from a specific tag group before creating it. This validation was not being run before the topic was being sent to a review queue for categories that have that setting enabled.

There was an existing validation in `TopicCreator` but it was not correct; it was only validating when the tags did _not_ exist and also only happened on `create`. I now run the validation in `TopicCreator.valid?`

I also improved the error message shown to the user when they have not added the tags required (showing the tag names from the tag group), and changed the composer tag selector to not show "optional" if there are N tags required from a certain group.

lib/topic_creator.rb

@@ -24,6 +24,15 @@ class TopicCreator
     # this allows us to add errors
     valid = topic.valid?
 
+    category = find_category
+    if category.present? && guardian.can_tag?(topic)
+      tags = @opts[:tags].present? ? Tag.where(name: @opts[:tags]) : (@opts[:tags] || [])
+
+      # both add to topic.errors
+      DiscourseTagging.validate_min_required_tags_for_category(guardian, topic, category, tags)
+      DiscourseTagging.validate_required_tags_from_group(guardian, topic, category, tags)
+    end
+
     DiscourseEvent.trigger(:after_validate_topic, topic, self)
     valid &&= topic.errors.empty?
 
@@ -160,21 +169,12 @@ class TopicCreator
   end
 
   def setup_tags(topic)
-    if @opts[:tags].blank?
-      unless @guardian.is_staff? || !guardian.can_tag?(topic)
-        category = find_category
+    return if @opts[:tags].blank?
 
-        if !DiscourseTagging.validate_min_required_tags_for_category(@guardian, topic, category) ||
-            !DiscourseTagging.validate_required_tags_from_group(@guardian, topic, category)
-          rollback_from_errors!(topic)
-        end
-      end
-    else
-      valid_tags = DiscourseTagging.tag_topic_by_names(topic, @guardian, @opts[:tags])
-      unless valid_tags
-        topic.errors.add(:base, :unable_to_tag)
-        rollback_from_errors!(topic)
-      end
+    valid_tags = DiscourseTagging.tag_topic_by_names(topic, @guardian, @opts[:tags])
+    unless valid_tags
+      topic.errors.add(:base, :unable_to_tag)
+      rollback_from_errors!(topic)
     end
   end