FIX: Return 422 when creating topics with tags w/out permission (#10400)

The UI prevents users from trying to create tags on topics when they
don't have permission, but if you are trying to add tags to a topic via
the API and you don't have permission before this change it would
silently succeed in creating the topic, but it wouldn't have any tags.

Now a 422 error will be returned with an error message when trying to
create a topic with tags when tagging is disabled or you don't have
enough trust level to add tags to a topic.

Bug report: https://meta.discourse.org/t/-/70525/14

config/locales/server.en.yml

@@ -530,6 +530,7 @@ en:
               reply_by_email_disabled: "Reply by email has been disabled."
               target_user_not_found: "One of the users you are sending this message to could not be found."
               unable_to_update: "There was an error updating that topic."
+              unable_to_tag: "There was an error tagging the topic."
             featured_link:
               invalid: "is invalid. URL should include http:// or https://."
               invalid_category: "can't be edited in this category."

lib/discourse_tagging.rb

@@ -112,8 +112,9 @@ module DiscourseTagging
         topic.tags = []
       end
       topic.tags_changed = true
+      return true
     end
-    true
+    false
   end
 
   def self.validate_min_required_tags_for_category(guardian, topic, category, tags = [])

lib/topic_creator.rb

@@ -165,7 +165,10 @@ class TopicCreator
       end
     else
       valid_tags = DiscourseTagging.tag_topic_by_names(topic, @guardian, @opts[:tags])
-      rollback_from_errors!(topic) unless valid_tags
+      unless valid_tags
+        topic.errors.add(:base, :unable_to_tag)
+        rollback_from_errors!(topic)
+      end
     end
   end
 

spec/components/new_post_manager_spec.rb

@@ -289,6 +289,9 @@ describe NewPostManager do
     it "calls custom enqueuing handlers" do
       Reviewable.set_priorities(high: 20.5)
       SiteSetting.reviewable_default_visibility = 'high'
+      SiteSetting.tagging_enabled = true
+      SiteSetting.min_trust_to_create_tag = 0
+      SiteSetting.min_trust_level_to_tag_topics = 0
 
       manager = NewPostManager.new(
         topic.user,

spec/components/post_creator_spec.rb

@@ -406,7 +406,7 @@ describe PostCreator do
 
           it "doesn't create tags" do
             expect { @post = creator_with_tags.create }.to change { Tag.count }.by(0)
-            expect(@post.topic.tags.size).to eq(0)
+            expect(@post.topic&.tags&.size).to eq(nil)
           end
         end
 

spec/models/reviewable_queued_post_spec.rb

@@ -143,6 +143,12 @@ RSpec.describe ReviewableQueuedPost, type: :model do
   context "creating a topic" do
     let(:reviewable) { Fabricate(:reviewable_queued_post_topic, category: category) }
 
+    before do
+      SiteSetting.tagging_enabled = true
+      SiteSetting.min_trust_to_create_tag = 0
+      SiteSetting.min_trust_level_to_tag_topics = 0
+    end
+
     context "editing" do
 
       it "is editable and returns the fields" do

spec/requests/posts_controller_spec.rb

@@ -970,6 +970,51 @@ describe PostsController do
         expect(json['errors']).to be_present
       end
 
+      it 'cannot create a post with a tag when tagging is disabled' do
+        SiteSetting.tagging_enabled = false
+        tag = Fabricate(:tag)
+
+        post "/posts.json", params: {
+          raw: 'this is the test content',
+          title: 'this is the test title for the topic',
+          tags: [tag.name],
+        }
+
+        expect(response.status).to eq(422)
+        json = response.parsed_body
+        expect(json['errors']).to be_present
+      end
+
+      it 'cannot create a post with a tag without tagging permission' do
+        SiteSetting.tagging_enabled = true
+        SiteSetting.min_trust_level_to_tag_topics = 4
+        tag = Fabricate(:tag)
+
+        post "/posts.json", params: {
+          raw: 'this is the test content',
+          title: 'this is the test title for the topic',
+          tags: [tag.name],
+        }
+
+        expect(response.status).to eq(422)
+        json = response.parsed_body
+        expect(json['errors']).to be_present
+      end
+
+      it 'can create a post with a tag when tagging is enabled' do
+        SiteSetting.tagging_enabled = true
+        tag = Fabricate(:tag)
+
+        post "/posts.json", params: {
+          raw: 'this is the test content',
+          title: 'this is the test title for the topic',
+          tags: [tag.name],
+        }
+
+        expect(response.status).to eq(200)
+        expect(Post.last.topic.tags.count).to eq(1)
+      end
+
       it 'creates the post' do
         post "/posts.json", params: {
           raw: 'this is the test content',