Make Admin::UsersController work with Ruby 2.6

Ruby 2.6 introduced `Enumerable#filter`, which takes no arguments.
Attempting to call `filter` on an `ActiveRecord::Relation` with a scope
will fail with a `wrong number of arguments (given 1, expected 0)`
message because the `Enumerable#filter` implementation overrides the
delegated `ActiveRecord::Relation#filter` method.

To make Admin::UsersController compatible with Ruby 2.6, rename
`User.filter` to `User.filter_items`.

app/controllers/admin/users_controller.rb

@@ -7,7 +7,7 @@ class Admin::UsersController < Admin::ApplicationController
   before_action :check_impersonation_availability, only: :impersonate
 
   def index
-    @users = User.order_name_asc.filter(params[:filter])
+    @users = User.filter_items(params[:filter]).order_name_asc
     @users = @users.search_with_secondary_emails(params[:search_query]) if params[:search_query].present?
     @users = @users.sort_by_attribute(@sort = params[:sort])
     @users = @users.page(params[:page])

app/models/user.rb

@@ -388,7 +388,7 @@ class User < ApplicationRecord
       find_by(id: user_id)
     end
 
-    def filter(filter_name)
+    def filter_items(filter_name)
       case filter_name
       when 'admins'
         admins

spec/controllers/admin/users_controller_spec.rb

@@ -8,6 +8,20 @@ describe Admin::UsersController do
     sign_in(admin)
   end
 
+  describe 'GET #index' do
+    it 'retrieves all users' do
+      get :index
+
+      expect(assigns(:users)).to match_array([user, admin])
+    end
+
+    it 'filters by admins' do
+      get :index, params: { filter: 'admins' }
+
+      expect(assigns(:users)).to eq([admin])
+    end
+  end
+
   describe 'GET :id' do
     it 'finds a user case-insensitively' do
       user = create(:user, username: 'CaseSensitive')

spec/models/user_spec.rb

@@ -976,43 +976,43 @@ describe User do
     end
   end
 
-  describe '.filter' do
+  describe '.filter_items' do
     let(:user) { double }
 
     it 'filters by active users by default' do
       expect(described_class).to receive(:active).and_return([user])
 
-      expect(described_class.filter(nil)).to include user
+      expect(described_class.filter_items(nil)).to include user
     end
 
     it 'filters by admins' do
       expect(described_class).to receive(:admins).and_return([user])
 
-      expect(described_class.filter('admins')).to include user
+      expect(described_class.filter_items('admins')).to include user
     end
 
     it 'filters by blocked' do
       expect(described_class).to receive(:blocked).and_return([user])
 
-      expect(described_class.filter('blocked')).to include user
+      expect(described_class.filter_items('blocked')).to include user
     end
 
     it 'filters by two_factor_disabled' do
       expect(described_class).to receive(:without_two_factor).and_return([user])
 
-      expect(described_class.filter('two_factor_disabled')).to include user
+      expect(described_class.filter_items('two_factor_disabled')).to include user
     end
 
     it 'filters by two_factor_enabled' do
       expect(described_class).to receive(:with_two_factor).and_return([user])
 
-      expect(described_class.filter('two_factor_enabled')).to include user
+      expect(described_class.filter_items('two_factor_enabled')).to include user
     end
 
     it 'filters by wop' do
       expect(described_class).to receive(:without_projects).and_return([user])
 
-      expect(described_class.filter('wop')).to include user
+      expect(described_class.filter_items('wop')).to include user
     end
   end