[FIX rubocop#4751] Rails/HasManyOrHasOneDependent shouldn't report of…

…fense if :through option was specified

CHANGELOG.md

@@ -9,6 +9,7 @@
 * [#4745](https://github.com/bbatsov/rubocop/issues/4745): Make `Style/SafeNavigation` ignore negated continuations. ([@drenmi][])
 * [#4732](https://github.com/bbatsov/rubocop/issues/4732): Prevent `Performance/HashEachMethods` from registering an offense when `#each` follows `#to_a`. ([@drenmi][])
 * [#4730](https://github.com/bbatsov/rubocop/issues/4730): False positive on Lint/InterpolationCheck. ([@koic][])
+* [#4751](https://github.com/bbatsov/rubocop/issues/4751): Prevent `Rails/HasManyOrHasOneDependent` cop from registering offense if `:through` option was specified. ([@smakagon][])
 
 ## 0.50.0 (2017-09-14)
 

lib/rubocop/cop/rails/has_many_or_has_one_dependent.rb

@@ -5,6 +5,7 @@ module Cop
     module Rails
       # This cop looks for `has_many` or `has_one` associations that don't
       # specify a `:dependent` option.
+      # It doesn't register an offense if `:through` option was specified.
       #
       # @example
       #   # bad
@@ -17,6 +18,7 @@ module Rails
       #   class User < ActiveRecord::Base
       #     has_many :comments, dependent: :restrict_with_exception
       #     has_one :avatar, dependent: :destroy
+      #     has_many :patients, through: :appointments
       #   end
       class HasManyOrHasOneDependent < Cop
         MSG = 'Specify a `:dependent` option.'.freeze
@@ -33,11 +35,17 @@ class HasManyOrHasOneDependent < Cop
           (pair (sym :dependent) !(:nil))
         PATTERN
 
+        def_node_matcher :has_through?, <<-PATTERN
+          (pair (sym :through) !(:nil))
+        PATTERN
+
         def on_send(node)
           unless is_has_many_or_has_one_without_options?(node)
             pairs = is_has_many_or_has_one_with_options?(node)
             return unless pairs
-            return if pairs.any? { |pair| has_dependent?(pair) }
+            return if pairs.any? do |pair|
+              has_dependent?(pair) || has_through?(pair)
+            end
           end
 
           add_offense(node, :selector)

manual/cops_rails.md

@@ -482,6 +482,7 @@ Enabled | No
 
 This cop looks for `has_many` or `has_one` associations that don't
 specify a `:dependent` option.
+It doesn't register an offense if `:through` option was specified.
 
 ### Example
 
@@ -496,6 +497,7 @@ end
 class User < ActiveRecord::Base
   has_many :comments, dependent: :restrict_with_exception
   has_one :avatar, dependent: :destroy
+  has_many :patients, through: :appointments
 end
 ```
 

spec/rubocop/cop/rails/has_many_or_has_one_dependent_spec.rb

@@ -25,6 +25,21 @@ class Person
     it 'does not register an offense when specifying `:dependent` strategy' do
       expect_no_offenses('has_one :foo, dependent: :bar')
     end
+
+    context 'with :through option' do
+      it 'does not register an offense for non-nil value' do
+        expect_no_offenses('has_one :foo, through: :bar')
+      end
+
+      it 'registers an offense for nil value' do
+        expect_offense(<<-RUBY.strip_indent)
+        class Person
+          has_one :foo, through: nil
+          ^^^^^^^ Specify a `:dependent` option.
+        end
+        RUBY
+      end
+    end
   end
 
   context 'has_many' do
@@ -49,5 +64,20 @@ class Person
     it 'does not register an offense when specifying `:dependent` strategy' do
       expect_no_offenses('has_many :foo, dependent: :bar')
     end
+
+    context 'with :through option' do
+      it 'does not register an offense for non-nil value' do
+        expect_no_offenses('has_many :foo, through: :bars')
+      end
+
+      it 'registers an offense for nil value' do
+        expect_offense(<<-RUBY.strip_indent)
+        class Person
+          has_many :foo, through: nil
+          ^^^^^^^^ Specify a `:dependent` option.
+        end
+        RUBY
+      end
+    end
   end
 end