Expose paths modified by a push from a pipeline class

app/models/ci/pipeline.rb

@@ -627,6 +627,18 @@ module Ci
       end
     end
 
+    def branch_updated?
+      strong_memoize(:branch_updated) do
+        push_details.branch_updated?
+      end
+    end
+
+    def modified_paths
+      strong_memoize(:changes) do
+        push_details.modified_paths
+      end
+    end
+
     private
 
     def ci_yaml_from_repo
@@ -650,6 +662,22 @@ module Ci
       Gitlab::DataBuilder::Pipeline.build(self)
     end
 
+    def push_details
+      strong_memoize(:push_details) do
+        Gitlab::Git::Push.new(project, before_sha, sha, push_ref)
+      end
+    end
+
+    def push_ref
+      if branch?
+        Gitlab::Git::BRANCH_REF_PREFIX + ref.to_s
+      elsif tag?
+        Gitlab::Git::TAG_REF_PREFIX + ref.to_s
+      else
+        raise ArgumentError, 'Invalid pipeline type!'
+      end
+    end
+
     def latest_builds_status
       return 'failed' unless yaml_errors.blank?
 

spec/models/ci/pipeline_spec.rb

@@ -825,6 +825,57 @@ describe Ci::Pipeline, :mailer do
     end
   end
 
+  describe '#branch_updated?' do
+    context 'when pipeline has before SHA' do
+      before do
+        pipeline.update_column(:before_sha, 'a1b2c3d4')
+      end
+
+      it 'runs on a branch update push' do
+        expect(pipeline.before_sha).not_to be Gitlab::Git::BLANK_SHA
+        expect(pipeline.branch_updated?).to be true
+      end
+    end
+
+    context 'when pipeline does not have before SHA' do
+      before do
+        pipeline.update_column(:before_sha, Gitlab::Git::BLANK_SHA)
+      end
+
+      it 'does not run on a branch updating push' do
+        expect(pipeline.branch_updated?).to be false
+      end
+    end
+  end
+
+  describe '#modified_paths' do
+    context 'when old and new revisions are set' do
+      let(:project) { create(:project, :repository) }
+
+      before do
+        pipeline.update(before_sha: '1234abcd', sha: '2345bcde')
+      end
+
+      it 'fetches stats for changes between commits' do
+        expect(project.repository)
+          .to receive(:diff_stats).with('1234abcd', '2345bcde')
+          .and_call_original
+
+        pipeline.modified_paths
+      end
+    end
+
+    context 'when either old or new revision is missing' do
+      before do
+        pipeline.update_column(:before_sha, Gitlab::Git::BLANK_SHA)
+      end
+
+      it 'raises an error' do
+        expect { pipeline.modified_paths }.to raise_error(ArgumentError)
+      end
+    end
+  end
+
   describe '#has_kubernetes_active?' do
     context 'when kubernetes is active' do
       shared_examples 'same behavior between KubernetesService and Platform::Kubernetes' do