Ignore ENV.update calls in Rails/SaveBang

CHANGELOG.md

@@ -12,6 +12,7 @@
 
 * [#12](https://github.com/rubocop-hq/rubocop-rails/issues/12): Fix a false positive for `Rails/SkipsModelValidations` when passing a boolean literal to `touch`. ([@eugeneius][])
 * [#238](https://github.com/rubocop-hq/rubocop-rails/issues/238): Fix auto correction for `Rails/IndexBy` when the `.to_h` invocation is separated in multiple lines. ([@diogoosorio][])
+* [#248](https://github.com/rubocop-hq/rubocop-rails/pull/248): Fix a false positive for `Rails/SaveBang` when `update` is called on `ENV`. ([@eugeneius][])
 
 ### Changes
 

lib/rubocop/cop/rails/save_bang.rb

@@ -246,6 +246,7 @@ def checked_immediately?(node)
 
         def allowed_receiver?(node)
           return false unless node.receiver
+          return true if node.receiver.const_name == 'ENV'
           return false unless cop_config['AllowedReceivers']
 
           cop_config['AllowedReceivers'].any? do |allowed_receiver|

spec/rubocop/cop/rails/save_bang_spec.rb

@@ -607,4 +607,8 @@ def find_or_create(**opts)
   it 'properly ignores lvasign without right hand side' do
     expect_no_offenses('variable += 1')
   end
+
+  it 'ignores update when called on ENV' do
+    expect_no_offenses('ENV.update("DISABLE_SPRING" => "1")')
+  end
 end