Add check for double negative in NegatedIf and NegatedWhile rules (…

…rubocop#3146)

Previously this file only looked at the first operator in the line.
With these changes there is now a pattern match to ensure `!!`
isn't flagged by these rules.

CHANGELOG.md

@@ -14,6 +14,7 @@
 * [#3125](https://github.com/bbatsov/rubocop/issues/3125): Fix `Rails/UniqBeforePluck` to ignore `uniq` with block. ([@tejasbubane][])
 * [#3116](https://github.com/bbatsov/rubocop/issues/3116): `Style/SpaceAroundKeyword` allows `&.` method calls after `super` and `yield`. ([@segiddins][])
 * [#3131](https://github.com/bbatsov/rubocop/issues/3131): Fix `Style/ZeroLengthPredicate` to ignore `size` and `length` variables. ([@tejasbubane][])
+* [#3146](https://github.com/bbatsov/rubocop/pull/3146): Fix `NegatedIf` and `NegatedWhile` to ignore double negations. ([@natalzia-paperless][])
 
 ## 0.40.0 (2016-05-09)
 
@@ -2168,3 +2169,4 @@
 [@tjwp]: https://github.com/tjwp
 [@neodelf]: https://github.com/neodelf
 [@josh]: https://github.com/josh
+[@natalzia-paperless]: https://github.com/natalzia-paperless

lib/rubocop/cop/mixin/negative_conditional.rb

@@ -6,17 +6,19 @@ module Cop
     # Some common code shared between FavorUnlessOverNegatedIf and
     # FavorUntilOverNegatedWhile.
     module NegativeConditional
+      def self.included(mod)
+        mod.def_node_matcher :single_negative?, '(send !(send _ :!) :!)'
+      end
+
       def check_negative_conditional(node)
         condition, _body, _rest = *node
 
         # Look at last expression of contents if there are parentheses
         # around condition.
         condition = condition.children.last while condition.type == :begin
-        return unless condition.type == :send
 
-        _object, method = *condition
-        return unless method == :! && !(node.loc.respond_to?(:else) &&
-                                        node.loc.else)
+        return unless single_negative?(condition) &&
+                      !(node.loc.respond_to?(:else) && node.loc.else)
 
         add_offense(node, :expression)
       end

spec/rubocop/cop/style/negated_if_spec.rb

@@ -68,6 +68,15 @@
     expect(cop.offenses).to be_empty
   end
 
+  it 'accepts an if where the condition is doubly negated' do
+    inspect_source(cop,
+                   ['if !!condition',
+                    '  some_method',
+                    'end',
+                    'some_method if !!condition'])
+    expect(cop.offenses).to be_empty
+  end
+
   it 'is not confused by negated elsif' do
     inspect_source(cop,
                    ['if test.is_a?(String)',

spec/rubocop/cop/style/negated_while_spec.rb

@@ -39,7 +39,7 @@
     expect(cop.offenses.map(&:line)).to eq([1, 4])
   end
 
-  it 'accepts an while where only part of the condition is negated' do
+  it 'accepts a while where only part of the condition is negated' do
     inspect_source(cop,
                    ['while !a_condition && another_condition',
                     '  some_method',
@@ -51,6 +51,15 @@
     expect(cop.messages).to be_empty
   end
 
+  it 'accepts a while where the condition is doubly negated' do
+    inspect_source(cop,
+                   ['while !!a_condition',
+                    '  some_method',
+                    'end',
+                    'some_method while !!a_condition'])
+    expect(cop.messages).to be_empty
+  end
+
   it 'autocorrects by replacing while not with until' do
     corrected = autocorrect_source(cop, ['something while !x.even?',
                                          'something while(!x.even?)'])