FIX: Allow redirection for slugs that start with digits

app/controllers/topics_controller.rb

@@ -60,6 +60,13 @@ class TopicsController < ApplicationController
     opts[:slow_platform] = true if slow_platform?
     opts[:username_filters] = username_filters.split(',') if username_filters.is_a?(String)
 
+    # Special case: a slug with a number in front should look by slug first before looking
+    # up that particular number
+    if params[:id] && params[:id] =~ /^\d+[^\d\\]+$/
+      topic = Topic.find_by(slug: params[:id].downcase)
+      return redirect_to_correct_topic(topic, opts[:post_number]) if topic && topic.visible
+    end
+
     begin
       @topic_view = TopicView.new(params[:id] || params[:topic_id], current_user, opts)
     rescue Discourse::NotFound

spec/controllers/topics_controller_spec.rb

@@ -569,6 +569,15 @@ describe TopicsController do
       expect(response).to redirect_to(topic.relative_url)
     end
 
+    it 'can find a topic when a slug has a number in front' do
+      another_topic = Fabricate(:post).topic
+
+      topic.update_column(:slug, "#{another_topic.id}-reasons-discourse-is-awesome")
+      xhr :get, :show, id: "#{another_topic.id}-reasons-discourse-is-awesome"
+
+      expect(response).to redirect_to(topic.relative_url)
+    end
+
     it 'keeps the post_number parameter around when redirecting' do
       xhr :get, :show, id: topic.slug, post_number: 42
       expect(response).to redirect_to(topic.relative_url + "/42")