Improve codeowner checks in BlobController

- fixes bug where checks unevenly applied to file create
- strip \n from error messages
- improve tests

ee/app/controllers/ee/projects/blob_controller.rb

@@ -11,19 +11,21 @@ module EE
 
       private
 
+      # rubocop:disable Gitlab/ModuleWithInstanceVariables
       def validate_codeowner_rules
         return unless ::Feature.enabled?(:use_legacy_codeowner_validations)
-        return if params[:file_path].blank?
+        return if @file_path.blank?
 
-        codeowners_error = codeowners_check_error(project, branch_name, params[:file_path])
+        codeowners_error = codeowners_check_error(project, branch_name, @file_path)
 
         if codeowners_error.present?
-          flash.now[:alert] = codeowners_error
+          flash.now[:alert] = codeowners_error.tr("\n", " ")
           view = params[:action] == 'update' ? :edit : :new
 
           render view
         end
       end
+      # rubocop:enable Gitlab/ModuleWithInstanceVariables
 
       def codeowners_check_error(project, branch_name, paths)
         ::Gitlab::CodeOwners::Validator.new(project, branch_name, paths).execute

ee/changelogs/unreleased/221199-unclear-error-is-shown-when-trying-to-update-codeowners-enabled-fi.yml

+---
+title: Fix issue with displaying Code Owner error messages in the UI
+merge_request: 34600
+author:
+type: fixed

ee/spec/controllers/ee/projects/blob_controller_spec.rb

@@ -4,6 +4,7 @@ require 'spec_helper'
 
 RSpec.describe Projects::BlobController do
   include ProjectForksHelper
+  include FakeBlobHelpers
 
   let(:project) { create(:project, :public, :repository) }
 
@@ -29,15 +30,34 @@ RSpec.describe Projects::BlobController do
   end
 
   shared_examples "renders to the expected_view with an error msg" do
-    let(:error_msg) { "Example error msg" }
-
-    it "renders to the expected_view with an error msg" do
-      default_params[:file_path] = "CHANGELOG"
+    let(:error_msg) do
+      "Pushes to protected branches that contain changes to files that match " \
+      "patterns defined in `CODEOWNERS` are disabled for this project. " \
+      "Please submit these changes via a merge request.  The following " \
+      "pattern(s) from `CODEOWNERS` were matched: - docs/ "
+    end
 
-      expect_next_instance_of(Gitlab::CodeOwners::Validator) do |validator|
-        expect(validator).to receive(:execute).and_return(error_msg)
+    before do
+      allow(::ProtectedBranch).to receive(:branch_requires_code_owner_approval?)
+        .and_return(true)
+
+      expect_next_instance_of(Repository) do |repo|
+        allow(repo).to receive(:code_owners_blob)
+          .with(ref: "master")
+          .and_return(
+            fake_blob(
+              path: "CODEOWNERS",
+              data: "*.rb @#{user.username}\ndocs/ @#{user.username}"
+            )
+          )
       end
 
+      stub_licensed_features(code_owner_approval_required: true)
+    end
+
+    it "renders to the edit page with an error msg" do
+      default_params[:file_path] = "docs/EXAMPLE_FILE"
+
       subject
 
       expect(flash[:alert]).to eq(error_msg)
@@ -53,7 +73,7 @@ RSpec.describe Projects::BlobController do
         project_id: project,
         id: 'master',
         branch_name: 'master',
-        file_name: 'CHANGELOG',
+        file_name: 'docs/EXAMPLE_FILE',
         content: 'Added changes',
         commit_message: 'Create CHANGELOG'
       }
@@ -68,7 +88,7 @@ RSpec.describe Projects::BlobController do
     it 'redirects to blob' do
       post :create, params: default_params
 
-      expect(response).to be_ok
+      expect(response).to be_redirect
     end
 
     it_behaves_like "file matches a codeowners rule" do
@@ -91,10 +111,6 @@ RSpec.describe Projects::BlobController do
       }
     end
 
-    def blob_after_edit_path
-      project_blob_path(project, 'master/CHANGELOG')
-    end
-
     before do
       project.add_maintainer(user)