Calculate modified paths of a git push operation

lib/gitlab/git/diff_stats_collection.rb

@@ -18,6 +18,10 @@ module Gitlab
         indexed_by_path[path]
       end
 
+      def paths
+        @collection.map(&:path)
+      end
+
       private
 
       def indexed_by_path

lib/gitlab/git/push.rb

@@ -28,6 +28,10 @@ module Gitlab
         Gitlab::Git.blank_ref?(@newrev)
       end
 
+      def branch_updated?
+        branch_push? && !branch_added? && !branch_removed?
+      end
+
       def force_push?
         Gitlab::Checks::ForcePush.force_push?(@project, @oldrev, @newrev)
       end
@@ -37,6 +41,16 @@ module Gitlab
           Gitlab::Git.branch_ref?(@ref)
         end
       end
+
+      def modified_paths
+        unless branch_updated?
+          raise ArgumentError, 'Unable to calculate modified paths!'
+        end
+
+        strong_memoize(:modified_paths) do
+          @project.repository.diff_stats(@oldrev, @newrev).paths
+        end
+      end
     end
   end
 end

spec/lib/gitlab/git/diff_stats_collection_spec.rb

@@ -14,7 +14,7 @@ describe Gitlab::Git::DiffStatsCollection do
   let(:diff_stats) { [stats_a, stats_b] }
   let(:collection) { described_class.new(diff_stats) }
 
-  describe '.find_by_path' do
+  describe '#find_by_path' do
     it 'returns stats by path when found' do
       expect(collection.find_by_path('foo')).to eq(stats_a)
     end
@@ -23,4 +23,10 @@ describe Gitlab::Git::DiffStatsCollection do
       expect(collection.find_by_path('no-file')).to be_nil
     end
   end
+
+  describe '#paths' do
+    it 'returns only modified paths' do
+      expect(collection.paths).to eq %w[foo bar]
+    end
+  end
 end

spec/lib/gitlab/git/push_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe Gitlab::Git::Push do
   set(:project) { create(:project, :repository) }
 
-  let(:oldrev) { project.commit('HEAD~10').id }
+  let(:oldrev) { project.commit('HEAD~2').id }
   let(:newrev) { project.commit.id }
   let(:ref) { 'refs/heads/some-branch' }
 
@@ -35,12 +35,36 @@ describe Gitlab::Git::Push do
     end
 
     context 'when it is a tag push' do
-      let(:ref) { 'refs/tags/my-branch' }
+      let(:ref) { 'refs/tags/my-tag' }
 
       it { is_expected.not_to be_branch_push }
     end
   end
 
+  describe '#branch_updated?' do
+    context 'when it is a branch push with correct old and new revisions' do
+      it { is_expected.to be_branch_updated }
+    end
+
+    context 'when it is not a branch push' do
+      let(:ref) { 'refs/tags/my-tag' }
+
+      it { is_expected.not_to be_branch_updated }
+    end
+
+    context 'when old revision is blank' do
+      let(:oldrev) { Gitlab::Git::BLANK_SHA }
+
+      it { is_expected.not_to be_branch_updated }
+    end
+
+    context 'when it is not a branch push' do
+      let(:newrev) { Gitlab::Git::BLANK_SHA }
+
+      it { is_expected.not_to be_branch_updated }
+    end
+  end
+
   describe '#force_push?' do
     context 'when old revision is an ancestor of the new revision' do
       let(:oldrev) { 'HEAD~3' }
@@ -80,4 +104,25 @@ describe Gitlab::Git::Push do
       it { is_expected.to be_branch_removed }
     end
   end
+
+  describe '#modified_paths' do
+    context 'when a push is a branch update' do
+      let(:oldrev) { '281d3a76f31c812dbf48abce82ccf6860adedd81' }
+      let(:new_rev) { '1b12f15a11fc6e62177bef08f47bc7b5ce50b141' }
+
+      it 'returns modified paths' do
+        expect(subject.modified_paths).to eq ['bar/branch-test.txt',
+                                              'files/js/commit.coffee',
+                                              'with space/README.md']
+      end
+    end
+
+    context 'when a push is not a branch update' do
+      let(:oldrev) { Gitlab::Git::BLANK_SHA }
+
+      it 'raises an error' do
+        expect { subject.modified_paths }.to raise_error(ArgumentError)
+      end
+    end
+  end
 end