[Fix rubocop#3308] Make Lint/NextWithoutAccumulator aware of nested…

… enumeration

This cop would register an offense if a nested block contained a `next`
without an accumulator, e.g.:

```
[(1..3), (4..6)].reduce(0) do |acc, elems|
  elems.each_with_index do |elem, i|
    next if i == 1
    acc << elem
  end
  acc
end
```

This fix addresses that, by checking if the direct block parent of any
offending `next` is indeed the block that we were inspecting.

CHANGELOG.md

@@ -18,6 +18,7 @@
 ### Changes
 
 * [#2645](https://github.com/bbatsov/rubocop/issues/2645): `Style/EmptyLiteral` no longer generates an offense for `String.new` when using frozen string literals. ([@drenmi][])
+* [#3308](https://github.com/bbatsov/rubocop/issues/3308): Make `Lint/NextWithoutAccumulator` aware of nested enumeration. ([@drenmi][])
 
 ## 0.41.2 (2016-07-07)
 

lib/rubocop/cop/lint/next_without_accumulator.rb

@@ -27,11 +27,19 @@ class NextWithoutAccumulator < Cop
 
         def on_block(node)
           on_body_of_reduce(node) do |body|
-            void_next = body.each_node(:next).find { |n| n.children.empty? }
+            void_next = body.each_node(:next).find do |n|
+              n.children.empty? && parent_block_node(n) == node
+            end
 
             add_offense(void_next, :expression) if void_next
           end
         end
+
+        private
+
+        def parent_block_node(node)
+          node.each_ancestor.find { |n| n.type == :block }
+        end
       end
     end
   end

spec/rubocop/cop/lint/next_without_accumulator_spec.rb

@@ -24,6 +24,18 @@ def code_with_accumulator(method_name)
     SOURCE
   end
 
+  def code_with_nested_block(method_name)
+    <<-SOURCE
+      [(1..3), (4..6)].#{method_name}(0) do |acc, elems|
+        elems.each_with_index do |elem, i|
+          next if i == 1
+          acc << elem
+        end
+        acc
+      end
+    SOURCE
+  end
+
   shared_examples 'reduce/inject' do |reduce_alias|
     context "given a #{reduce_alias} block" do
       it 'registers an offense for a bare next' do
@@ -36,11 +48,16 @@ def code_with_accumulator(method_name)
         inspect_source(cop, code_with_accumulator(reduce_alias))
         expect(cop.offenses).to be_empty
       end
+
+      it 'accepts next within a nested block' do
+        inspect_source(cop, code_with_nested_block(reduce_alias))
+        expect(cop.offenses).to be_empty
+      end
     end
   end
 
-  include_examples 'reduce/inject', :reduce
-  include_examples 'reduce/inject', :inject
+  it_behaves_like 'reduce/inject', :reduce
+  it_behaves_like 'reduce/inject', :inject
 
   context 'given an unrelated block' do
     it 'accepts a bare next' do