FIX: Remove tag plugin code from tag hashtag check.

app/assets/javascripts/discourse/lib/link-tag-hashtag.js.es6

@@ -28,7 +28,7 @@ export function linkSeenTagHashtags($elem) {
 
   if ($hashtags.length) {
     const tagValues = $hashtags.map((_, hashtag) => {
-      return $(hashtag).text().substr(1).replace(`${TAG_HASHTAG_POSTFIX}`, "");
+      return $(hashtag).text().substr(1).replace(TAG_HASHTAG_POSTFIX, "");
     });
 
     if (tagValues.length) {

app/controllers/tags_controller.rb

@@ -177,8 +177,8 @@ class TagsController < ::ApplicationController
   def check_hashtag
     tag_values = params[:tag_values].each(&:downcase!)
 
-    valid_tags = TopicCustomField.where(name: DiscourseTagging::TAGS_FIELD_NAME, value: tag_values).map do |tag|
-      { value: tag.value, url: "#{Discourse.base_url}/tags/#{tag.value}" }
+    valid_tags = Tag.where(name: tag_values).map do |tag|
+      { value: tag.name, url: tag.full_url }
     end.compact
 
     render json: { valid: valid_tags }

app/models/tag.rb

@@ -34,6 +34,10 @@ class Tag < ActiveRecord::Base
   def self.include_tags?
     SiteSetting.tagging_enabled && SiteSetting.show_filter_by_tag
   end
+
+  def full_url
+    "#{Discourse.base_url}/tags/#{self.name}"
+  end
 end
 
 # == Schema Information

spec/integration/tags_spec.rb

@@ -0,0 +1,20 @@
+require 'rails_helper'
+
+describe "Tags" do
+  before do
+    SiteSetting.tagging_enabled = true
+  end
+
+  describe "checking tag hashtags" do
+    let(:tag) { Fabricate(:tag, name: 'test') }
+
+    it "should return the right response" do
+      get "/tags/check.json", { tag_values: [tag.name] }
+
+      expect(response).to be_success
+
+      tag = JSON.parse(response.body)["valid"].first
+      expect(tag["value"]).to eq('test')
+    end
+  end
+end