Apply codeowner validation when creating/updating a blob in the UI

app/controllers/concerns/check_codeowner_rules.rb

+# frozen_string_literal: true
+
+module CheckCodeownerRules
+  extend ActiveSupport::Concern
+
+  def codeowners_check_error(project, branch_name, paths)
+    ::Gitlab::CodeOwners::Validator.new(project, branch_name, paths).execute
+  end
+end

app/controllers/projects/blob_controller.rb

@@ -9,6 +9,7 @@ class Projects::BlobController < Projects::ApplicationController
   include ActionView::Helpers::SanitizeHelper
   include RedirectsForMissingPathOnTree
   include SourcegraphDecorator
+  include CheckCodeownerRules
 
   prepend_before_action :authenticate_user!, only: [:edit]
 
@@ -28,6 +29,7 @@ class Projects::BlobController < Projects::ApplicationController
   before_action :editor_variables, except: [:show, :preview, :diff]
   before_action :validate_diff_params, only: :diff
   before_action :set_last_commit_sha, only: [:edit, :update]
+  before_action :validate_codeowner_rules, only: [:create, :update]
 
   before_action only: :show do
     push_frontend_feature_flag(:code_navigation, @project)
@@ -71,6 +73,7 @@ class Projects::BlobController < Projects::ApplicationController
 
   def update
     @path = params[:file_path] if params[:file_path].present?
+
     create_commit(Files::UpdateService, success_path: -> { after_edit_path },
                                         failure_view: :edit,
                                         failure_path: project_blob_path(@project, @id))
@@ -115,6 +118,19 @@ class Projects::BlobController < Projects::ApplicationController
 
   private
 
+  def validate_codeowner_rules
+    return if params[:file_path].blank?
+
+    codeowners_error = codeowners_check_error(@project, @branch_name, params[:file_path])
+
+    if codeowners_error.present?
+      flash.now[:alert] = codeowners_error
+      view = params[:action] == 'update' ? :edit : :new
+
+      render view
+    end
+  end
+
   def blob
     @blob ||= @repository.blob_at(@commit.id, @path)
 

spec/controllers/projects/blob_controller_spec.rb

@@ -250,6 +250,56 @@ describe Projects::BlobController do
     end
   end
 
+  shared_examples "file matches a codeowners rule" do
+    let(:error_msg) { "Example error msg" }
+
+    it "renders to the edit page with an error msg" do
+      default_params[:file_path] = "CHANGELOG"
+
+      expect_next_instance_of(Gitlab::CodeOwners::Validator) do |validator|
+        expect(validator).to receive(:execute).and_return(error_msg)
+      end
+
+      subject
+
+      expect(flash[:alert]).to eq(error_msg)
+      expect(response).to render_template(expected_view)
+    end
+  end
+
+  describe 'POST create' do
+    let(:user) { create(:user) }
+    let(:default_params) do
+      {
+        namespace_id: project.namespace,
+        project_id: project,
+        id: 'master',
+        branch_name: 'master',
+        file_name: 'CHANGELOG',
+        content: 'Added changes',
+        commit_message: 'Create CHANGELOG'
+      }
+    end
+
+    before do
+      project.add_developer(user)
+
+      sign_in(user)
+    end
+
+    it 'redirects to blob' do
+      post :create, params: default_params
+
+      expect(response).to be_ok
+    end
+
+    it_behaves_like "file matches a codeowners rule" do
+      subject { post :create, params: default_params }
+
+      let(:expected_view) { :new }
+    end
+  end
+
   describe 'PUT update' do
     let(:user) { create(:user) }
     let(:default_params) do
@@ -279,6 +329,12 @@ describe Projects::BlobController do
       expect(response).to redirect_to(blob_after_edit_path)
     end
 
+    it_behaves_like "file matches a codeowners rule" do
+      subject { put :update, params: default_params }
+
+      let(:expected_view) { :edit }
+    end
+
     context '?from_merge_request_iid' do
       let(:merge_request) { create(:merge_request, source_project: project, target_project: project) }
       let(:mr_params) { default_params.merge(from_merge_request_iid: merge_request.iid) }