Sort the network graph both by commit date and topographically.30973-network-graph-sorted-by-date-and-topo

- Previously, we sorted commits by date, which seemed to work okay.

- The one edge case where this failed was when multiple commits have the same
  commit date (for example: when a range of commits are cherry picked with a
  single command, they all have the same commit date [and different author
  dates]).

- Commits with the same commit date would be sorted arbitrarily, and usually
  break the network graph.

- This commit solves the problem by both sorting by date, and by sorting
  topographically (parents aren't displayed until all their children are
  displayed)

- Include review comments from @adamniedzielski

A more detailed explanation is present here:
https://gitlab.com/gitlab-org/gitlab-ce/issues/30973#note_28706230

1 files changed, 10 insertions, 7 deletions

diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index acd0037ee4f..684b2e72875 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -499,8 +499,9 @@ module Gitlab
       #     :contains is the commit contained by the refs from which to begin (SHA1 or name)
       #     :max_count is the maximum number of commits to fetch
       #     :skip is the number of commits to skip
-      #     :order is the commits order and allowed value is :none (default), :date, or :topo
-      #        commit ordering types are documented here:
+      #     :order is the commits order and allowed value is :none (default), :date,
+      #        :topo, or any combination of them (in an array). Commit ordering types
+      #        are documented here:
       #        http://www.rubydoc.info/github/libgit2/rugged/Rugged#SORT_NONE-constant)
       #
       def find_commits(options = {})
@@ -1290,16 +1291,18 @@ module Gitlab
         raise CommandError.new(e)
       end
 
-      # Returns the `Rugged` sorting type constant for a given
-      # sort type key. Valid keys are `:none`, `:topo`, and `:date`
-      def rugged_sort_type(key)
+      # Returns the `Rugged` sorting type constant for one or more given
+      # sort types. Valid keys are `:none`, `:topo`, and `:date`, or an array
+      # containing more than one of them. `:date` uses a combination of date and
+      # topological sorting to closer mimic git's native ordering.
+      def rugged_sort_type(sort_type)
         @rugged_sort_types ||= {
           none: Rugged::SORT_NONE,
           topo: Rugged::SORT_TOPO,
-          date: Rugged::SORT_DATE
+          date: Rugged::SORT_DATE | Rugged::SORT_TOPO
         }
 
-        @rugged_sort_types.fetch(key, Rugged::SORT_NONE)
+        @rugged_sort_types.fetch(sort_type, Rugged::SORT_NONE)
       end
     end
   end