Use wiki.disk_path

app/services/projects/destroy_service.rb

@@ -51,7 +51,7 @@ module Projects
     end
     def wiki_path
-      repo_path + '.wiki'
+      project.wiki.disk_path
     end
     def trash_repositories!

lib/github/import.rb

@@ -74,7 +74,7 @@ module Github
     def fetch_wiki_repository
       return if project.wiki.repository_exists?
-      wiki_path = "#{project.disk_path}.wiki"
+      wiki_path = project.wiki.disk_path
       gitlab_shell.import_repository(project.repository_storage_path, wiki_path, wiki_url)
     rescue Gitlab::Shell::Error => e
       # GitHub error message when the wiki repo has not been created,

lib/gitlab/github_import/wiki_formatter.rb

@@ -8,7 +8,7 @@ module Gitlab
       end
       def disk_path
-        "#{project.disk_path}.wiki"
+        project.wiki.disk_path
       end
       def import_url

spec/lib/gitlab/github_import/wiki_formatter_spec.rb

@@ -11,7 +11,7 @@ describe Gitlab::GithubImport::WikiFormatter do
   describe '#disk_path' do
     it 'appends .wiki to project path' do
-      expect(wiki.disk_path).to eq project.disk_path + '.wiki'
+      expect(wiki.disk_path).to eq project.wiki.disk_path
     end
   end