Refactor Import/Export permission error

The permission error is shared between Group and project  import/export
so move this to the error class so that the functionality can be shared
by the different call sites.

app/services/groups/import_export/export_service.rb

@@ -24,12 +24,7 @@ module Groups
 
       def validate_user_permissions
         unless @current_user.can?(:admin_group, @group)
-          @shared.error(
-            ::Gitlab::ImportExport::Error.new(
-              "User with ID: %s does not have permission to Group %s with ID: %s." %
-              [@current_user.id, @group.name, @group.id]
-            )
-          )
+          @shared.error(::Gitlab::ImportExport::Error.permission_error(@current_user, @group))
 
           notify_error!
         end

app/services/groups/import_export/import_service.rb

@@ -52,12 +52,7 @@ module Groups
         if current_user.can?(:admin_group, group)
           true
         else
-          @shared.error(
-            Gitlab::ImportExport::Error.new(
-              "User with ID: %s does not have permission to Group %s with ID: %s." %
-              [current_user.id, group.name, group.id]
-            )
-          )
+          @shared.error(::Gitlab::ImportExport::Error.permission_error(current_user, group))
 
           false
         end

app/services/projects/import_export/export_service.rb

@@ -5,9 +5,7 @@ module Projects
     class ExportService < BaseService
       def execute(after_export_strategy = nil, options = {})
         unless project.template_source? || can?(current_user, :admin_project, project)
-          raise ::Gitlab::ImportExport::Error.new(
-            "User with ID: %s does not have permission to Project %s with ID: %s." %
-              [current_user.id, project.name, project.id])
+          raise ::Gitlab::ImportExport::Error.permission_error(current_user, project)
         end
 
         @shared = project.import_export_shared

lib/gitlab/import_export/error.rb

@@ -2,6 +2,13 @@
 
 module Gitlab
   module ImportExport
-    Error = Class.new(StandardError)
+    class Error < StandardError
+      def self.permission_error(user, importable)
+        self.new(
+          "User with ID: %s does not have required permissions for %s: %s with ID: %s" %
+          [user.id, importable.class.name, importable.name, importable.id]
+        )
+      end
+    end
   end
 end

spec/lib/gitlab/import_export/error_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::ImportExport::Error do
+  describe '.permission_error' do
+    subject(:error) do
+      described_class.permission_error(user, importable)
+    end
+
+    let(:user) { build(:user, id: 1) }
+
+    context 'when supplied a project' do
+      let(:importable) { build(:project, id: 1, name: 'project1') }
+
+      it 'returns an error with the correct message' do
+        expect(error.message)
+          .to eq 'User with ID: 1 does not have required permissions for Project: project1 with ID: 1'
+      end
+    end
+
+    context 'when supplied a group' do
+      let(:importable) { build(:group, id: 1, name: 'group1') }
+
+      it 'returns an error with the correct message' do
+        expect(error.message)
+          .to eq 'User with ID: 1 does not have required permissions for Group: group1 with ID: 1'
+      end
+    end
+  end
+end

spec/services/groups/import_export/export_service_spec.rb

@@ -39,7 +39,7 @@ describe Groups::ImportExport::ExportService do
       let(:service) { described_class.new(group: group, user: another_user, params: { shared: shared }) }
 
       let(:expected_message) do
-        "User with ID: %s does not have permission to Group %s with ID: %s." %
+        "User with ID: %s does not have required permissions for Group: %s with ID: %s" %
           [another_user.id, group.name, group.id]
       end
 

spec/services/groups/import_export/import_service_spec.rb

@@ -61,7 +61,7 @@ describe Groups::ImportExport::ImportService do
         allow(Gitlab::ImportExport::Shared).to receive(:new).and_return(shared)
 
         expect(shared).to receive(:error) do |param|
-          expect(param.message).to include 'does not have permission to'
+          expect(param.message).to include 'does not have required permissions for'
         end
 
         expect { subject }.to raise_error(Gitlab::ImportExport::Error)

spec/services/projects/import_export/export_service_spec.rb

@@ -164,7 +164,7 @@ describe Projects::ImportExport::ExportService do
 
       it 'fails' do
         expected_message =
-          "User with ID: %s does not have permission to Project %s with ID: %s." %
+          "User with ID: %s does not have required permissions for Project: %s with ID: %s" %
             [another_user.id, project.name, project.id]
         expect { service.execute }.to raise_error(Gitlab::ImportExport::Error).with_message(expected_message)
       end