Support auto-correction in WordArray.

Part of solution for rubocop#743.

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#714](https://github.com/bbatsov/rubocop/issues/714): New cop `RequireParentheses` checks for method calls without parentheses together with a boolean operator indicating that a mistake about precedence may have been made. ([@jonas054][])
+* [#743](https://github.com/bbatsov/rubocop/issues/743): `WordArray` cop does auto-correction. ([@jonas054][])
 
 ### Changes
 

lib/rubocop/cop/style/word_array.rb

@@ -53,6 +53,33 @@ def complex_content?(arr_sexp)
         def min_size
           cop_config['MinSize']
         end
+
+        def autocorrect(node)
+          sb = node.loc.expression.source_buffer
+          interpolated = false
+
+          contents = node.children.map do |n|
+            if character_literal?(n)
+              interpolated = true
+              begin_pos = n.loc.expression.begin_pos + '?'.length
+              end_pos = n.loc.expression.end_pos
+            else
+              begin_pos = n.loc.begin.end_pos
+              end_pos = n.loc.end.begin_pos
+            end
+            Parser::Source::Range.new(sb, begin_pos, end_pos).source
+          end.join(' ')
+
+          char = interpolated ? 'W' : 'w'
+
+          @corrections << lambda do |corrector|
+            corrector.replace(node.loc.expression, "%#{char}(#{contents})")
+          end
+        end
+
+        def character_literal?(node)
+          node.loc.end.nil?
+        end
       end
     end
   end

spec/rubocop/cop/style/word_array_spec.rb

@@ -84,4 +84,14 @@
 
     expect(cop.offences.size).to eq(1)
   end
+
+  it 'auto-corrects an array of words' do
+    new_source = autocorrect_source(cop, "['one', %q(two), 'three']")
+    expect(new_source).to eq('%w(one two three)')
+  end
+
+  it 'auto-corrects an array of words and character constants' do
+    new_source = autocorrect_source(cop, '[%{one}, %Q(two), ?\n, ?\t]')
+    expect(new_source).to eq('%W(one two \n \t)')
+  end
 end