FIX: Process tag synonyms when approving reviewable queued post (#30810)

Followup 72c4709a5ab26f00e32b65d874b3a206d679181e

Previously we made a fix to allow skip validations when tagging
a topic via TopicCreator. However, this flow also skips a lot of
the more in-depth work on tags we do when creating a topic, like
processing tag synonyms. When approving reviewable queued posts,
we skip validations, so this would cause an issue where a topic
was approved and the tag synonyms weren't applied.

This commit changes the logic so we attempt the more complete
`DiscourseTagging.tag_topic_by_names` call first and if this fails
and skip validations is on, then we do
`DiscourseTagging.add_or_create_tags_by_name`.
This at least gives a chance for the full workflow to work first.

lib/topic_creator.rb

@@ -192,11 +192,14 @@ class TopicCreator
 
   def setup_tags(topic)
     if @opts[:tags].present?
-      if @opts[:skip_validations]
-        DiscourseTagging.add_or_create_tags_by_name(topic, @opts[:tags])
-      else
-        valid_tags = DiscourseTagging.tag_topic_by_names(topic, @guardian, @opts[:tags])
-        unless valid_tags
+      # We can try the full tagging workflow which does validations and other
+      # things like replacing synonyms first, but if this fails then we can try
+      # the simple workflow if validations are skipped.
+      valid_tags = DiscourseTagging.tag_topic_by_names(topic, @guardian, @opts[:tags])
+      if !valid_tags
+        if @opts[:skip_validations]
+          DiscourseTagging.add_or_create_tags_by_name(topic, @opts[:tags])
+        else
           topic.errors.add(:base, :unable_to_tag)
           rollback_from_errors!(topic)
         end

spec/models/reviewable_queued_post_spec.rb

@@ -320,6 +320,16 @@ RSpec.describe ReviewableQueuedPost, type: :model do
       expect(Topic.count).to eq(topic_count)
       expect(Post.count).to eq(post_count)
     end
+
+    it "remaps tags with synonyms when approved" do
+      syn_tag = Fabricate(:tag, name: "syntag", target_tag: Fabricate(:tag, name: "maintag"))
+      reviewable.payload["tags"] += ["syntag"]
+
+      result = reviewable.perform(moderator, :approve_post)
+
+      expect(result.success?).to eq(true)
+      expect(result.created_post_topic.tags.pluck(:name)).to match_array(%w[cool neat maintag])
+    end
   end
 
   describe "Callbacks" do