FIX: tag input detects when a tag is not allowed and won't offer to create it anyway

app/assets/javascripts/discourse/components/tag-chooser.js.es6

@@ -43,6 +43,8 @@ export default Ember.TextField.extend({
       this.set('allowCreate', site.get('can_create_tag'));
     }
 
+    this.set('termMatchesForbidden', false);
+
     if (this.get('unlimitedTagCount')) {
       limit = null;
     } else if (this.get('limit')) {
@@ -78,7 +80,7 @@ export default Ember.TextField.extend({
         term = term.replace(filterRegexp, '').trim();
 
         // No empty terms, make sure the user has permission to create the tag
-        if (!term.length || !self.get('allowCreate')) return;
+        if (!term.length || !self.get('allowCreate') || self.get('termMatchesForbidden')) return;
 
         if ($(data).filter(function() {
           return this.text.localeCompare(term) === 0;
@@ -119,6 +121,7 @@ export default Ember.TextField.extend({
           if (self.siteSettings.tags_sort_alphabetically) {
             data.results = data.results.sort(function(a,b) { return a.id > b.id; });
           }
+          self.set('termMatchesForbidden', data.forbidden ? true : false);
           return data;
         }
       },

app/controllers/tags_controller.rb

@@ -156,7 +156,15 @@ class TagsController < ::ApplicationController
       tags << { id: t.name, text: t.name, count: 0 }
     end
 
-    render json: { results: tags }
+    json_response = { results: tags }
+
+    t = DiscourseTagging.clean_tag(params[:q])
+    if Tag.where(name: t).exists? && !tags.find { |h| h[:id] == t }
+      # filter_allowed_tags determined that the tag entered is not allowed
+      json_response[:forbidden] = t
+    end
+
+    render json: json_response
   end
 
   def notifications

spec/controllers/tags_controller_spec.rb

@@ -39,4 +39,38 @@ describe TagsController do
       end
     end
   end
+
+  describe 'search' do
+    context 'tagging disabled' do
+      it "returns 404" do
+        xhr :get, :search, q: 'stuff'
+        expect(response.status).to eq(404)
+      end
+    end
+
+    context 'tagging enabled' do
+      before do
+        SiteSetting.tagging_enabled = true
+      end
+
+      it "can return some tags" do
+        tag_names = ['stuff', 'stinky', 'stumped']
+        tag_names.each { |name| Fabricate(:tag, name: name) }
+        xhr :get, :search, q: 'stu'
+        expect(response).to be_success
+        json = ::JSON.parse(response.body)
+        expect(json["results"].map{|j| j["id"]}.sort).to eq(['stuff', 'stumped'])
+      end
+
+      it "can say if given tag is not allowed" do
+        yup, nope = Fabricate(:tag, name: 'yup'), Fabricate(:tag, name: 'nope')
+        category = Fabricate(:category, tags: [yup])
+        xhr :get, :search, q: 'nope', categoryId: category.id
+        expect(response).to be_success
+        json = ::JSON.parse(response.body)
+        expect(json["results"].map{|j| j["id"]}.sort).to eq([])
+        expect(json["forbidden"]).to be_present
+      end
+    end
+  end
 end