[Fix rubocop#3142] Fix Style/Lambda whitespacing when auto-correct un…

…parenthesized arguments (rubocop#3160)

CHANGELOG.md

@@ -18,6 +18,7 @@
 * [#3146](https://github.com/bbatsov/rubocop/pull/3146): Fix `NegatedIf` and `NegatedWhile` to ignore double negations. ([@natalzia-paperless][])
 * [#3140](https://github.com/bbatsov/rubocop/pull/3140): `Style/FrozenStringLiteralComment` works with file doesn't have any tokens. ([@pocke][])
 * [#3154](https://github.com/bbatsov/rubocop/issues/3154): Fix handling of `()` in `Style/RedundantParentheses`. ([@lumeet][])
+* [#3160](https://github.com/bbatsov/rubocop/pull/3160): `Style/Lambda` fix whitespacing when auto-correcting unparenthesized arguments. ([@palkan][])
 
 ### Changes
 

lib/rubocop/cop/style/lambda.rb

@@ -137,6 +137,10 @@ def autocorrect(node)
 
         def autocorrect_literal_to_method(corrector, node)
           block_method, args = *node
+
+          # Check for unparenthesized args' preceding and trailing whitespaces.
+          remove_unparenthesized_whitespaces(corrector, node)
+
           # Avoid correcting to `lambdado` by inserting whitespace
           # if none exists before or after the lambda arguments.
           if needs_whitespace?(block_method, args, node)
@@ -181,6 +185,24 @@ def arg_to_unparenthesized_call?(node)
           index = parent.children.index { |c| c.equal?(node) }
           index >= 2
         end
+
+        def remove_unparenthesized_whitespaces(corrector, node)
+          block_method, args = *node
+          return unless unparenthesized_literal_args?(args)
+          # First, remove leading whitespaces (beetween arrow and args)
+          corrector.remove_preceding(
+            args.source_range,
+            args.source_range.begin_pos - block_method.source_range.end_pos
+          )
+
+          # Then, remove trailing whitespaces (beetween args and 'do')
+          delta = node.loc.begin.begin_pos - args.source_range.end_pos - 1
+          corrector.remove_preceding(node.loc.begin, delta)
+        end
+
+        def unparenthesized_literal_args?(args)
+          args.source_range && args.source_range.begin && !parentheses?(args)
+        end
       end
     end
   end

spec/rubocop/cop/style/lambda_spec.rb

@@ -279,6 +279,48 @@
                                            '  x',
                                            'end'].join("\n")
         end
+
+        context 'without parentheses' do
+          let(:source) do
+            ['-> hello do',
+             '  puts hello',
+             'end']
+          end
+
+          it_behaves_like 'registers an offense',
+                          'Use the `lambda` method for multiline lambdas.'
+          it_behaves_like 'auto-correct', ['lambda do |hello|',
+                                           '  puts hello',
+                                           'end'].join("\n")
+        end
+
+        context 'with no parentheses and bad spacing' do
+          let(:source) do
+            ['->   hello  do',
+             '  puts hello',
+             'end']
+          end
+
+          it_behaves_like 'registers an offense',
+                          'Use the `lambda` method for multiline lambdas.'
+          it_behaves_like 'auto-correct', ['lambda do |hello|',
+                                           '  puts hello',
+                                           'end'].join("\n")
+        end
+
+        context 'with no parentheses and many args' do
+          let(:source) do
+            ['->   hello, user  do',
+             '  puts hello',
+             'end']
+          end
+
+          it_behaves_like 'registers an offense',
+                          'Use the `lambda` method for multiline lambdas.'
+          it_behaves_like 'auto-correct', ['lambda do |hello, user|',
+                                           '  puts hello',
+                                           'end'].join("\n")
+        end
       end
     end