Merge branch 'wiki-fix-reloaded' into 'master'

Use the relative url prefix for links in Wiki

Retry of gitlab-org/gitlab-ce!4026

@rymai !4050 solved all other problems how it looks like. I [tested](https://gitlab.com/artem-forks/gitlab-ce/commit/ff01eca7b559efa7cacf3412aa01cd8ae8a6db7e/builds) this with ruby22

Fixes #17071 



See merge request !4131

CHANGELOG

@@ -57,6 +57,9 @@ v 8.8.0 (unreleased)
   - Add counter metrics for rails cache
   - Import pull requests from GitHub where the source or target branches were removed
 
+v 8.7.6
+  - Fix links on wiki pages for relative url setups. !4131 (Artem Sidorenko)
+
 v 8.7.5
   - Fix relative links in wiki pages. !4050
   - Fix always showing build notification message when switching between merge requests !4086

app/models/project_wiki.rb

@@ -40,7 +40,7 @@ class ProjectWiki
   end
 
   def wiki_base_path
-    ["/", @project.path_with_namespace, "/wikis"].join('')
+    [Gitlab.config.gitlab.relative_url_root, "/", @project.path_with_namespace, "/wikis"].join('')
   end
 
   # Returns the Gollum::Wiki object.

lib/gitlab/url_builder.rb

@@ -62,7 +62,7 @@ module Gitlab
     end
 
     def wiki_page_url
-      "#{Gitlab.config.gitlab.url}#{object.wiki.wiki_base_path}/#{object.slug}"
+      namespace_project_wiki_url(object.wiki.project.namespace, object.wiki.project, object.slug)
     end
   end
 end

spec/models/project_wiki_spec.rb

@@ -38,7 +38,8 @@ describe ProjectWiki, models: true do
 
   describe "#wiki_base_path" do
     it "returns the wiki base path" do
-      wiki_base_path = "/#{project.path_with_namespace}/wikis"
+      wiki_base_path = "#{Gitlab.config.gitlab.relative_url_root}/#{project.path_with_namespace}/wikis"
+
       expect(subject.wiki_base_path).to eq(wiki_base_path)
     end
   end