Add auto-correct to DotPosition cop

Fix rubocop#1279

CHANGELOG.md

@@ -10,6 +10,7 @@
 * `UselessAssignment` cop now suggests a variable name for possible typos if there's a variable-ish identifier similar to the unused variable name in the same scope. ([@yujinakayama][])
 * [#1272](https://github.com/bbatsov/rubocop/issues/1272): `Tab` cop does auto-correction. ([@yous][])
 * [#1274](https://github.com/bbatsov/rubocop/issues/1274): `MultilineIfThen` cop does auto-correction. ([@bbatsov][])
+* [#1279](https://github.com/bbatsov/rubocop/issues/1279): `DotPosition` cop does auto-correction. ([@yous][])
 
 ### Bugs fixed
 

lib/rubocop/cop/style/dot_position.rb

@@ -51,6 +51,26 @@ def proper_dot_position?(node)
           when :trailing then dot_line != selector_line
           end
         end
+
+        def autocorrect(node)
+          receiver, _method_name, *_args = *node
+          if node.loc.selector
+            selector = node.loc.selector
+          else
+            # l.(1) has no selector, so we use the opening parenthesis instead
+            selector = node.loc.begin
+          end
+
+          @corrections << lambda do |corrector|
+            corrector.remove(node.loc.dot)
+            case style
+            when :leading
+              corrector.insert_before(selector, '.')
+            when :trailing
+              corrector.insert_after(receiver.loc.expression, '.')
+            end
+          end
+        end
       end
     end
   end

spec/rubocop/cop/style/dot_position_spec.rb

@@ -45,6 +45,31 @@
       inspect_source(cop, ['something.method_name'])
       expect(cop.offenses).to be_empty
     end
+
+    it 'auto-corrects trailing dot in multi-line call' do
+      new_source = autocorrect_source(cop, ['something.',
+                                            '  method_name'])
+      expect(new_source).to eq(['something',
+                                '  .method_name'].join("\n"))
+    end
+
+    it 'auto-corrects trailing dot in multi-line call without selector' do
+      new_source = autocorrect_source(cop, ['something.',
+                                            '  (1)'])
+      expect(new_source).to eq(['something',
+                                '  .(1)'].join("\n"))
+    end
+
+    it 'auto-corrects correct + opposite style' do
+      new_source = autocorrect_source(cop, ['something',
+                                            '  .method_name',
+                                            'something.',
+                                            '  method_name'])
+      expect(new_source).to eq(['something',
+                                '  .method_name',
+                                'something',
+                                '  .method_name'].join("\n"))
+    end
   end
 
   context 'Trailing dots style' do
@@ -87,5 +112,19 @@
                            'compact.join("\n")'])
       expect(cop.offenses).to be_empty
     end
+
+    it 'auto-corrects leading dot in multi-line call' do
+      new_source = autocorrect_source(cop, ['something',
+                                            '  .method_name'])
+      expect(new_source).to eq(['something.',
+                                '  method_name'].join("\n"))
+    end
+
+    it 'auto-corrects leading dot in multi-line call without selector' do
+      new_source = autocorrect_source(cop, ['something',
+                                            '  .(1)'])
+      expect(new_source).to eq(['something.',
+                                '  (1)'].join("\n"))
+    end
   end
 end