FIX: permalinks redirect on subfolder installs could add the subfolder to the url twice

app/controllers/permalinks_controller.rb

@@ -11,7 +11,7 @@ class PermalinksController < ApplicationController
     if permalink.external_url
       redirect_to permalink.external_url, status: :moved_permanently
     elsif permalink.target_url
-      redirect_to "#{Discourse::base_uri}#{permalink.target_url}", status: :moved_permanently
+      redirect_to permalink.target_url, status: :moved_permanently
     else
       raise Discourse::NotFound
     end

app/models/permalink.rb

@@ -75,7 +75,7 @@ class Permalink < ActiveRecord::Base
 
   def target_url
     return external_url if external_url
-    return post.url if post
+    return "#{Discourse::base_uri}#{post.url}" if post
     return topic.relative_url if topic
     return category.url if category
     nil

spec/controllers/permalinks_controller_spec.rb

@@ -10,6 +10,16 @@ describe PermalinksController do
       expect(response.status).to eq(301)
     end
 
+    it "should work for subfolder installs too" do
+      GlobalSetting.stubs(:relative_url_root).returns('/forum')
+      Discourse.stubs(:base_uri).returns("/forum")
+      permalink = Fabricate(:permalink)
+      Permalink.any_instance.stubs(:target_url).returns('/forum/t/the-topic-slug/42')
+      get :show, url: permalink.url
+      expect(response).to redirect_to('/forum/t/the-topic-slug/42')
+      expect(response.status).to eq(301)
+    end
+
     it "should apply normalizations" do
       SiteSetting.permalink_normalizations = "/(.*)\\?.*/\\1"