[Fix #4322] Fix Style/MultilineMemoization autocorrection

Author: dpostorivo

CHANGELOG.md

@@ -65,6 +65,7 @@
 * [#4646](https://github.com/bbatsov/rubocop/issues/4646): Make `Lint/Debugger` aware of `Kernel` and cbase. ([@pocke][])
 * [#4643](https://github.com/bbatsov/rubocop/issues/4643): Modify `Style/InverseMethods` to not register a separate offense for an inverse method nested inside of the block of an inverse method offense. ([@rrosenblum][])
 * [#4593](https://github.com/bbatsov/rubocop/issues/4593): Fix false positive in `Rails/SaveBang` when `save/update_attribute` is used with a `case` statement. ([@theRealNG][])
+* [#4322](https://github.com/bbatsov/rubocop/issues/4322): Fix Style/MultilineMemoization from autocorrecting to invalid ruby. ([@dpostorivo][])
 
 ### Changes
 

lib/rubocop/cop/style/multiline_memoization.rb

@@ -54,8 +54,7 @@ def on_or_asgn(node)
         def autocorrect(node)
           lambda do |corrector|
             if style == :keyword
-              corrector.replace(node.loc.begin, 'begin')
-              corrector.replace(node.loc.end, 'end')
+              keyword_autocorrect(node, corrector)
             else
               corrector.replace(node.loc.begin, '(')
               corrector.replace(node.loc.end, ')')
@@ -71,6 +70,29 @@ def bad_rhs?(rhs)
             rhs.kwbegin_type?
           end
         end
+
+        def keyword_autocorrect(node, corrector)
+          node_buf = node.source_range.source_buffer
+          corrector.replace(node.loc.begin, keyword_begin_str(node, node_buf))
+          corrector.replace(node.loc.end, keyword_end_str(node, node_buf))
+        end
+
+        def keyword_begin_str(node, node_buf)
+          indent = config.for_cop('IndentationWidth')['Width'] || 2
+          if node_buf.source[node.loc.begin.end_pos] == "\n"
+            'begin'
+          else
+            "begin\n" + (' ' * (node.loc.column + indent))
+          end
+        end
+
+        def keyword_end_str(node, node_buf)
+          if node_buf.source_line(node.loc.end.line) =~ /[^\s\)]/
+            "\n" + (' ' * node.loc.column) + 'end'
+          else
+            'end'
+          end
+        end
       end
     end
   end

spec/rubocop/cop/style/multiline_memoization_spec.rb

@@ -121,6 +121,18 @@
                                 baz
                               end
                           RUBY
+
+          it_behaves_like 'code with offense',
+                          <<-RUBY.strip_indent,
+                            foo ||= (bar ||
+                                     baz)
+                          RUBY
+                          <<-RUBY.strip_indent
+                             foo ||= begin
+                                       bar ||
+                                      baz
+                                     end
+                          RUBY
         end
       end