Show modified and added public paths in MR

app/models/environment_status.rb

@@ -24,4 +24,33 @@ class EnvironmentStatus
   def deployed_at
     deployment&.created_at
   end
+
+  def changes
+    sha = merge_request.diff_head_sha
+    return [] if project.route_map_for(sha).nil?
+
+    changed_files.map { |file| build_change(file, sha) }.compact
+  end
+
+  def changed_files
+    merge_request.merge_request_diff
+      .merge_request_diff_files.where(deleted_file: false)
+  end
+
+  private
+
+  PAGE_EXTENSIONS = /\A\.(s?html?|php|asp|cgi|pl)\z/i.freeze
+
+  def build_change(file, sha)
+    public_path = project.public_path_for_source_path(file.new_path, sha)
+    return if public_path.nil?
+
+    ext = File.extname(public_path)
+    return if ext.present? && ext !~ PAGE_EXTENSIONS
+
+    {
+      path: public_path,
+      external_url: environment.external_url_for(file.new_path, sha)
+    }
+  end
 end

app/serializers/environment_status_entity.rb

@@ -36,6 +36,8 @@ class EnvironmentStatusEntity < Grape::Entity
     es.deployment.try(:formatted_deployment_time)
   end
 
+  expose :changes, if: ->(*) { Feature.enabled?(:ci_environments_status_changes, project) }
+
   private
 
   def environment

spec/models/environment_status_spec.rb

@@ -30,4 +30,32 @@ describe EnvironmentStatus do
 
     it { is_expected.to eq(deployment) }
   end
+
+  # $ git diff --stat pages-deploy-target...pages-deploy
+  # .gitlab/route-map.yml              |  5 +++++
+  # files/html/500.html                | 13 -------------
+  # files/html/page.html               |  3 +++
+  # files/js/application.js            |  3 +++
+  # files/markdown/ruby-style-guide.md |  4 ++++
+  # pages-deploy.txt                   |  1 +
+  #
+  # $ cat .gitlab/route-map.yml
+  # - source: /files\/markdown\/(.+)\.md$/
+  #   public: '\1.html'
+  #
+  # - source: /files\/(.+)/
+  #   public: '\1'
+  describe '#changes' do
+    it 'contains only added and modified public pages' do
+      expect(environment_status.changes).to contain_exactly(
+        {
+          path: 'ruby-style-guide.html',
+          external_url: "#{environment.external_url}/ruby-style-guide.html"
+        }, {
+          path: 'html/page.html',
+          external_url: "#{environment.external_url}/html/page.html"
+        }
+      )
+    end
+  end
 end

spec/serializers/environment_status_entity_spec.rb

@@ -25,11 +25,20 @@ describe EnvironmentStatusEntity do
   it { is_expected.to include(:external_url_formatted) }
   it { is_expected.to include(:deployed_at) }
   it { is_expected.to include(:deployed_at_formatted) }
+  it { is_expected.to include(:changes) }
 
   it { is_expected.not_to include(:stop_url) }
   it { is_expected.not_to include(:metrics_url) }
   it { is_expected.not_to include(:metrics_monitoring_url) }
 
+  context 'when :ci_environments_status_changes feature flag is disabled' do
+    before do
+      stub_feature_flags(ci_environments_status_changes: false)
+    end
+
+    it { is_expected.not_to include(:changes) }
+  end
+
   context 'when the user is project maintainer' do
     before do
       project.add_maintainer(user)