Remove native git calls from MR. Dump diff as array, not class

app/models/merge_request.rb

@@ -24,8 +24,6 @@ require Rails.root.join("lib/static_model")
 class MergeRequest < ActiveRecord::Base
   include Issuable
 
-  BROKEN_DIFF = "--broken-diff"
-
   attr_accessible :title, :assignee_id, :target_branch, :source_branch, :milestone_id,
                   :author_id_of_changes, :state_event
 
@@ -109,22 +107,18 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def diffs
-    st_diffs || []
+    load_diffs(st_diffs) || []
   end
 
   def reloaded_diffs
     if opened? && unmerged_diffs.any?
-      self.st_diffs = unmerged_diffs
+      self.st_diffs = dump_diffs(unmerged_diffs)
       self.save
     end
-
-  rescue Grit::Git::GitTimeout
-    self.st_diffs = [BROKEN_DIFF]
-    self.save
   end
 
   def broken_diffs?
-    diffs == [BROKEN_DIFF]
+    diffs == [Gitlab::Git::Diff::BROKEN_DIFF]
   end
 
   def valid_diffs?
@@ -132,11 +126,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def unmerged_diffs
-    # Only show what is new in the source branch compared to the target branch, not the other way around.
-    # The linex below with merge_base is equivalent to diff with three dots (git diff branch1...branch2)
-    # From the git documentation: "git diff A...B" is equivalent to "git diff $(git-merge-base A B) B"
-    common_commit = project.repo.git.native(:merge_base, {}, [target_branch, source_branch]).strip
-    diffs = project.repo.diff(common_commit, source_branch)
+    project.repository.diffs_between(source_branch, target_branch)
   end
 
   def last_commit
@@ -222,4 +212,12 @@ class MergeRequest < ActiveRecord::Base
   def load_commits(array)
     array.map { |hash| Commit.new(Gitlab::Git::Commit.new(hash)) }
   end
+
+  def dump_diffs(diffs)
+    diffs.map(&:to_hash)
+  end
+
+  def load_diffs(array)
+    array.map { |hash| Gitlab::Git::Diff.new(hash) }
+  end
 end