Adds pipeline editor link on root Ci config files

- Adds pipeline editor button on root config file
- This takes the user to ci/editor on master branch by default

app/views/projects/blob/_header.html.haml

@@ -9,6 +9,8 @@
     - else
       = edit_blob_button(@project, @ref, @path, blob: blob)
       = ide_edit_button(@project, @ref, @path, blob: blob)
+      - if can_view_pipeline_editor?(@project) && @path == @project.ci_config_path_or_default
+        = link_to "Pipeline Editor", project_ci_pipeline_editor_path(@project), class: "btn gl-button btn-confirm-secondary gl-ml-3"
     .btn-group{ role: "group", class: ("gl-ml-3" if current_user) }>
       = render_if_exists 'projects/blob/header_file_locks_link'
       - if current_user

spec/features/projects/blobs/user_views_pipeline_editor_button_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'User views pipeline editor button on root ci config file', :js do
+  include BlobSpecHelpers
+
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project) { create(:project, :public, :repository) }
+
+  context "when the ci config is the root file" do
+    before do
+      stub_feature_flags(consolidated_edit_button: false)
+      project.add_developer(user)
+      sign_in(user)
+    end
+
+    it 'shows the button to the Pipeline Editor' do
+      project.update!(ci_config_path: '.my-config.yml')
+      project.repository.create_file(user, project.ci_config_path_or_default, 'test', message: 'testing', branch_name: 'master')
+      visit project_blob_path(project, File.join('master', '.my-config.yml'))
+
+      expect(page).to have_content('Pipeline Editor')
+    end
+
+    it 'does not shows the Pipeline Editor button' do
+      project.repository.create_file(user, '.my-sub-config.yml', 'test', message: 'testing', branch_name: 'master')
+      visit project_blob_path(project, File.join('master', '.my-sub-config.yml'))
+
+      expect(page).not_to have_content('Pipeline Editor')
+    end
+  end
+
+  context "when user cannot collaborate" do
+    before do
+      stub_feature_flags(consolidated_edit_button: false)
+      sign_in(user)
+    end
+    it 'does not shows the Pipeline Editor button' do
+      visit project_blob_path(project, File.join('master', '.my-config.yml'))
+      expect(page).not_to have_content('Pipeline Editor')
+    end
+  end
+end