Fix EE for new diff notes

app/models/merge_request.rb

@@ -679,12 +679,8 @@ class MergeRequest < ActiveRecord::Base
     end
   end
 
-  def source_sha_parent
-    source_project.repository.commit(first_commit.sha).parents.first.sha
-  end
-
   def ff_merge_possible?
-    project.repository.is_ancestor?(target_sha, source_sha)
+    project.repository.is_ancestor?(target_branch_sha, diff_head_sha)
   end
 
   def should_be_rebased?

app/services/merge_requests/ff_merge_service.rb

@@ -9,7 +9,7 @@ module MergeRequests
     private
 
     def commit
-      repository.ff_merge(current_user, merge_request.source_sha, merge_request.target_branch)
+      repository.ff_merge(current_user, merge_request.diff_head_sha, merge_request.target_branch)
     end
   end
 end

features/steps/project/ff_merge_requests.rb

@@ -54,14 +54,14 @@ class Spinach::Features::ProjectFfMergeRequests < Spinach::FeatureSteps
   step 'merge request "Bug NS-05" is rebased' do
     merge_request.source_branch = 'flatten-dir'
     merge_request.target_branch = 'improve/awesome'
-    merge_request.reload_code
+    merge_request.reload_diff
     merge_request.save!
   end
 
   step 'merge request "Bug NS-05" merged target' do
     merge_request.source_branch = 'merged-target'
     merge_request.target_branch = 'improve/awesome'
-    merge_request.reload_code
+    merge_request.reload_diff
     merge_request.save!
   end
 

spec/models/merge_request_spec.rb

@@ -335,12 +335,6 @@ describe MergeRequest, models: true do
     end
   end
 
-  describe "#source_sha_parent" do
-    it "returns the sha of the parent commit of the first commit in the MR" do
-      expect(subject.source_sha_parent).to eq("ae73cb07c9eeaf35924a10f713b364d32b2dd34f")
-    end
-  end
-
   describe '#diverged_commits_count' do
     let(:project)      { create(:project) }
     let(:fork_project) { create(:project, forked_from_project: project) }