[Fix rubocop#435] Fix a false negative for Rails/BelongsTo

Fixes rubocop#435.

This PR fixes a false negative for `Rails/BelongsTo`
when using `belongs_to` lambda block with `required: false`.

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Change log
 
+### Bug fixes
+
+* [#435](https://github.com/rubocop-hq/rubocop-rails/issues/435): Fix a false negative for `Rails/BelongsTo` when using `belongs_to` lambda block with `required: false`. ([@koic][])
+
 ## master (unreleased)
 
 ### Bug fixes

lib/rubocop/cop/rails/belongs_to.rb

@@ -68,7 +68,7 @@ class BelongsTo < Base
         RESTRICT_ON_SEND = %i[belongs_to].freeze
 
         def_node_matcher :match_belongs_to_with_options, <<~PATTERN
-          (send _ :belongs_to _
+          (send _ :belongs_to ...
             (hash <$(pair (sym :required) ${true false}) ...>)
           )
         PATTERN

spec/rubocop/cop/rails/belongs_to_spec.rb

@@ -23,6 +23,17 @@
     RUBY
   end
 
+  it 'registers an offense and corrects when using `belongs_to` lambda block with `required: false`' do
+    expect_offense(<<~RUBY)
+      belongs_to :foo, -> { bar }, required: false
+      ^^^^^^^^^^ You specified `required: false`, in Rails > 5.0 the required option is deprecated and you want to use `optional: true`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      belongs_to :foo, -> { bar }, optional: true
+    RUBY
+  end
+
   it 'registers no offense when setting `optional: true`' do
     expect_no_offenses('belongs_to :foo, optional: true')
   end