Do not register an offense for TrailingUnderscoreVariable preceeded b…

…y a splat variable

CHANGELOG.md

@@ -13,6 +13,7 @@
 * [#2275](https://github.com/bbatsov/rubocop/pull/2275): Copy default `Exclude` into `Exclude` lists in `.rubocop_todo.yml`. ([@jonas054][])
 * `Style/IfUnlessModifier` accepts blocks followed by a chained call. ([@lumeet][])
 * [#2261](https://github.com/bbatsov/rubocop/issues/2261): Make relative `Exclude` paths in `$HOME/.rubocop_todo.yml` be relative to current directory. ([@jonas054][])
+* [#2246](https://github.com/bbatsov/rubocop/pull/2246): Do not register an offense for `Style/TrailingUnderscoreVariable` when the underscore variable is preceeded by a splat variable. ([@rrosenblum][])
 
 ## 0.34.2 (21/09/2015)
 

lib/rubocop/cop/style/trailing_underscore_variable.rb

@@ -15,6 +15,8 @@ module Style
       #   #good
       #   a, b, = foo()
       #   a, = foo()
+      #   *a, b, _ = foo()  => We need to know to not include 2 variables in a
+      #   a, *b, _ = foo()  => The correction `a, *b, = foo()` is a syntax error
       class TrailingUnderscoreVariable < Cop
         include SurroundingSpace
 
@@ -71,6 +73,13 @@ def find_first_offense(variables)
             first_offense = variable
           end
 
+          return nil if first_offense.nil?
+
+          first_offense_index = variables.index(first_offense)
+          0.upto(first_offense_index - 1).each do |index|
+            return nil if variables[index].splat_type?
+          end
+
           first_offense
         end
 

spec/rubocop/cop/style/trailing_underscore_variable_spec.rb

@@ -65,6 +65,56 @@
       expect(cop.messages).to be_empty
     end
 
+    it 'does not register an offense for an underscore preceeded by a ' \
+       'splat variable anywhere in the argument chain' do
+      inspect_source(cop, '*a, b, _ = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'does not register an offense for an underscore preceeded by a ' \
+       'splat variable' do
+      inspect_source(cop, 'a, *b, _ = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'does not register an offense for multiple underscores preceeded by a ' \
+       'splat variable' do
+      inspect_source(cop, 'a, *b, _, _ = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'does not register an offense for multiple named underscores ' \
+       'preceeded by a splat variable' do
+      inspect_source(cop, 'a, *b, _c, _d = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'registers an offense for multiple underscore variables preceeded by ' \
+       'a splat underscore variable' do
+      inspect_source(cop, 'a, *_, _, _ = foo()')
+
+      expect(cop.messages)
+        .to eq(['Do not use trailing `_`s in parallel assignment.'])
+    end
+
+    it 'does not register an offense for a named underscore variable ' \
+       'preceeded by a splat variable' do
+      inspect_source(cop, 'a, *b, _c = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'does not register an offense for a named variable preceeded by a ' \
+       'names splat underscore variable' do
+      inspect_source(cop, 'a, *b, _c = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
     describe 'autocorrect' do
       it 'removes trailing underscores automatically' do
         new_source = autocorrect_source(cop, 'a, b, _ = foo()')
@@ -120,6 +170,13 @@
                           })
     end
 
+    it 'does not register an offense for an underscore variable preceeded ' \
+       'by a named splat underscore variable' do
+      inspect_source(cop, 'a, *_b, _ = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
     it 'does not register an offense for named variables ' \
        'that start with an underscore' do
       inspect_source(cop, 'a, b, _c = foo()')
@@ -133,6 +190,20 @@
 
       expect(cop.messages).to be_empty
     end
+
+    it 'does not register an offense for an underscore preceeded by ' \
+       'a named splat underscore' do
+      inspect_source(cop, 'a, *_b, _ = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'does not register an offense for multiple underscore variables ' \
+       'preceeded by a named splat underscore variable' do
+      inspect_source(cop, 'a, *_b, _, _ = foo()')
+
+      expect(cop.messages).to be_empty
+    end
   end
 
   context 'configured to not allow named underscore variables' do
@@ -161,6 +232,37 @@
         .to eq(['Do not use trailing `_`s in parallel assignment.'])
     end
 
+    it 'does not register an offense for a named underscore preceeded by a ' \
+       'splat variable' do
+      inspect_source(cop, 'a, *b, _c = foo()')
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'registers an offense for an underscore variable preceeded ' \
+       'by a named splat underscore variable' do
+      inspect_source(cop, 'a, *_b, _ = foo()')
+
+      expect(cop.messages)
+        .to eq(['Do not use trailing `_`s in parallel assignment.'])
+    end
+
+    it 'registers an offense for an underscore preceeded by ' \
+       'a named splat underscore' do
+      inspect_source(cop, 'a, b, *_c, _ = foo()')
+
+      expect(cop.messages)
+        .to eq(['Do not use trailing `_`s in parallel assignment.'])
+    end
+
+    it 'registers an offense for multiple underscore variables ' \
+       'preceeded by a named splat underscore variable' do
+      inspect_source(cop, 'a, *_b, _, _ = foo()')
+
+      expect(cop.messages)
+        .to eq(['Do not use trailing `_`s in parallel assignment.'])
+    end
+
     context 'autocorrect' do
       it 'removes named underscore variables' do
         new_source = autocorrect_source(cop, 'a, _b = foo()')
@@ -173,6 +275,12 @@
 
         expect(new_source).to eq('a, = foo()')
       end
+
+      it 'removes named splat underscore and named underscore variables' do
+        new_source = autocorrect_source(cop, 'a, *_b, _c = foo()')
+
+        expect(new_source).to eq('a, = foo()')
+      end
     end
   end
 end