Merge branch '21446-service-external-wiki-only-works-when-project-wiki-is-enabled' into 'master'

Fix "Wiki" link not appearing in navigation for projects with external wiki

## Are there points in the code the reviewer needs to double check?

No

## What are the relevant issue numbers?

Closes #21446

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6057

2 files changed, 5 insertions, 1 deletions

diff --git a/app/models/ability.rb b/app/models/ability.rb
index a49dd703926..c1df4a865f6 100644
--- a/app/models/ability.rb
+++ b/app/models/ability.rb
@@ -355,7 +355,7 @@ class Ability
         rules += named_abilities('project_snippet')
       end
 
-      unless project.wiki_enabled
+      unless project.has_wiki?
         rules += named_abilities('wiki')
       end
 
diff --git a/app/models/project.rb b/app/models/project.rb
index 8cf093be4c3..edf536e2f98 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -680,6 +680,10 @@ class Project < ActiveRecord::Base
     update_column(:has_external_issue_tracker, services.external_issue_trackers.any?)
   end
 
+  def has_wiki?
+    wiki_enabled? || has_external_wiki?
+  end
+
   def external_wiki
     if has_external_wiki.nil?
       cache_has_external_wiki # Populate