Flush all repository caches when deleting a repo

This ensures that _all_ caches (including any caches normally only
flushed under certain conditions) are flushed whenever a project is
removed. Because cache keys are based on project namespaces (excluding
IDs) not doing so could result in a newly created project re-using old
caches (if the project was re-created using the same name).

app/models/repository.rb

@@ -238,6 +238,15 @@ class Repository
     expire_branch_cache(branch_name)
   end
 
+  # Expires _all_ caches, including those that would normally only be expired
+  # under specific conditions.
+  def expire_all_caches!
+    expire_cache
+    expire_root_ref_cache
+    expire_emptiness_caches
+    expire_has_visible_content_cache
+  end
+
   def expire_branch_cache(branch_name = nil)
     # When we push to the root branch we have to flush the cache for all other
     # branches as their statistics are based on the commits relative to the

app/services/projects/destroy_service.rb

@@ -16,11 +16,15 @@ module Projects
       return false unless can?(current_user, :remove_project, project)
 
       project.team.truncate
-      project.repository.expire_cache unless project.empty_repo?
 
       repo_path = project.path_with_namespace
       wiki_path = repo_path + '.wiki'
 
+      # Flush the cache for both repositories. This has to be done _before_
+      # removing the physical repositories as some expiration code depends on
+      # Git data (e.g. a list of branch names).
+      flush_caches(project, wiki_path)
+
       Project.transaction do
         project.destroy!
 
@@ -70,5 +74,13 @@ module Projects
     def removal_path(path)
       "#{path}+#{project.id}#{DELETED_FLAG}"
     end
+
+    def flush_caches(project, wiki_path)
+      project.repository.expire_all_caches! if project.repository.exists?
+
+      wiki_repo = Repository.new(wiki_path, project)
+
+      wiki_repo.expire_all_caches! if wiki_repo.exists?
+    end
   end
 end