[Fix #764] Handle heredocs in TrailingComma

There was a bug that made the cop consider commas inside heredocs as
trailing commas if the heredoc was part of the last item in a list.

CHANGELOG.md

@@ -10,6 +10,10 @@
 
 * [#762](https://github.com/bbatsov/rubocop/issues/762): Support Rainbow gem both 1.99.x and 2.x. ([@yujinakayama][])
 
+### Bugs fixed
+
+* [#764](https://github.com/bbatsov/rubocop/issues/764): Handle heredocs in `TrailingComma`. ([@jonas054][])
+
 ## 0.17.0 (25/01/2014)
 
 ### New features

lib/rubocop/cop/style/trailing_comma.rb

@@ -48,6 +48,9 @@ def check_literal(node, kind)
         def check(node, items, kind, begin_pos, end_pos)
           sb = items.first.loc.expression.source_buffer
           after_last_item = Parser::Source::Range.new(sb, begin_pos, end_pos)
+
+          return if heredoc?(after_last_item.source)
+
           comma_offset = after_last_item.source =~ /,/
           should_have_comma = style == :comma && multiline?(node)
           if comma_offset
@@ -60,6 +63,10 @@ def check(node, items, kind, begin_pos, end_pos)
           end
         end
 
+        def heredoc?(source_after_last_item)
+          source_after_last_item =~ /\w/
+        end
+
         # Returns true if the node has round/square/curly brackets.
         def brackets?(node)
           !node.loc.end.nil?

spec/rubocop/cop/style/trailing_comma_spec.rb

@@ -130,6 +130,16 @@
                              '           )'])
         expect(cop.offences).to be_empty
       end
+
+      it 'accepts comma inside a heredoc' +
+        ' parameters at the end' do
+        inspect_source(cop, ['route(help: {',
+                             "  'auth' => <<-HELP.chomp",
+                             ',',
+                             'HELP',
+                             '})'])
+        expect(cop.offences).to be_empty
+      end
     end
 
     context 'when EnforcedStyleForMultiline is comma' do
@@ -195,6 +205,17 @@
                              '           )'])
         expect(cop.offences).to be_empty
       end
+
+      it 'accepts missing comma after a heredoc' do
+        # A heredoc that's the last item in a literal or parameter list can not
+        # have a trailing comma. It's a syntax error.
+        inspect_source(cop, ['route(help: {',
+                             "  'auth' => <<-HELP.chomp",
+                             '...',
+                             'HELP',
+                             '},)']) # We still need a comma after the hash.
+        expect(cop.offences).to be_empty
+      end
     end
   end
 end