Fix loading database.yml file with aliases

changelog/fix_loading_database_yml_with_aliases.md

@@ -0,0 +1 @@
+* [#947](https://github.com/rubocop/rubocop-rails/issues/947): Fix loading `database.yml` file with aliases. ([@fatkodima][])

lib/rubocop/cop/rails/bulk_change_table.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'yaml'
+
 module RuboCop
   module Cop
     module Rails
@@ -192,11 +194,8 @@ def database_from_yaml
         def database_yaml
           return nil unless File.exist?('config/database.yml')
 
-          yaml = if YAML.respond_to?(:unsafe_load_file)
-                   YAML.unsafe_load_file('config/database.yml')
-                 else
-                   YAML.load_file('config/database.yml')
-                 end
+          src = File.read('config/database.yml')
+          yaml = load_yaml(src)
           return nil unless yaml.is_a? Hash
 
           config = yaml['development']
@@ -207,6 +206,14 @@ def database_yaml
           nil
         end
 
+        def load_yaml(src)
+          if Psych::VERSION > '4.0'
+            YAML.safe_load(src, aliases: true)
+          else
+            YAML.load(src) # rubocop:disable Security/YAMLLoad
+          end
+        end
+
         def support_bulk_alter?
           case database
           when MYSQL

spec/rubocop/cop/rails/bulk_change_table_spec.rb

@@ -440,36 +440,35 @@ def change
   end
 
   context 'when `database.yml` is exists' do
-    let(:yaml) { nil }
+    let(:yaml) { '' }
 
     before do
       allow(File).to receive(:exist?).with('config/database.yml').and_return(true)
-      if YAML.respond_to?(:unsafe_load_file)
-        allow(YAML).to receive(:unsafe_load_file).with('config/database.yml').and_return(yaml)
-      else
-        allow(YAML).to receive(:load_file).with('config/database.yml').and_return(yaml)
-      end
+      allow(File).to receive(:read).and_call_original
+      allow(File).to receive(:read).with('config/database.yml').and_return(yaml)
     end
 
     context 'mysql2' do
       let(:yaml) do
-        {
-          'development' => {
-            'adapter' => 'mysql2'
-          }
-        }
+        <<~YAML
+          default: &default
+            adapter: mysql2
+          development:
+            <<: *default
+        YAML
       end
 
       it_behaves_like 'offense for mysql'
     end
 
     context 'postgresql' do
       let(:yaml) do
-        {
-          'development' => {
-            'adapter' => 'postgresql'
-          }
-        }
+        <<~YAML
+          default: &default
+            adapter: postgresql
+          development:
+            <<: *default
+        YAML
       end
 
       context 'with Rails 5.2', :rails52 do