[Fix rubocop#3450] Prevent Style/TernaryParentheses from making uns…

…afe corrections

This cop, when configured to omit parentheses, would remove them even when the
condition contained an unparenthesized method call, e.g.:

```
foo = (bar? baz) ? 'Yes' : 'No'
```

which would change the semantics of the expression. This change fixes that.

CHANGELOG.md

@@ -40,6 +40,7 @@
 * [#3423](https://github.com/bbatsov/rubocop/issues/3423): Checks if .rubocop is a file before parsing. ([@joejuzl][])
 * [#3439](https://github.com/bbatsov/rubocop/issues/3439): Fix variable assignment check not working properly when a block is used in `Rails/SaveBang`. ([@QuinnHarris][])
 * [#3401](https://github.com/bbatsov/rubocop/issues/3401): Read file contents in binary mode so `Style/EndOfLine` works on Windows. ([@jonas054][])
+* [#3450](https://github.com/bbatsov/rubocop/issues/3450): Prevent `Style/TernaryParentheses` cop from making unsafe corrections. ([@drenmi][])
 
 ### Changes
 

lib/rubocop/cop/style/ternary_parentheses.rb

@@ -67,8 +67,8 @@ def autocorrect(node)
               corrector.insert_before(condition.source_range, '(')
               corrector.insert_after(condition.source_range, ')')
             else
-              # Don't correct if it's a safe assignment
-              unless safe_assignment?(condition)
+              unless safe_assignment?(condition) ||
+                     unsafe_autocorrect?(condition)
                 corrector.remove(condition.loc.begin)
                 corrector.remove(condition.loc.end)
               end
@@ -101,6 +101,23 @@ def infinite_loop?
           require_parentheses? &&
             redundant_parentheses_enabled?
         end
+
+        def unsafe_autocorrect?(condition)
+          condition.children.any? do |child|
+            unparenthesized_method_call?(child)
+          end
+        end
+
+        def unparenthesized_method_call?(child)
+          argument = method_call_argument(child)
+
+          argument && argument !~ /^\(/
+        end
+
+        def_node_matcher :method_call_argument, <<-PATTERN
+          {(:defined? $...)
+           (send {(send ...) nil} _ $(send nil _)...)}
+        PATTERN
       end
     end
   end

spec/rubocop/cop/style/ternary_parentheses_spec.rb

@@ -146,6 +146,28 @@
                         'foo = (bar = baz = find_baz) ? a : b'
       end
     end
+
+    context 'with an unparenthesized method call condition' do
+      it_behaves_like 'code with offense',
+                      'foo = (defined? bar) ? a : b',
+                      'foo = (defined? bar) ? a : b'
+
+      it_behaves_like 'code with offense',
+                      'foo = (baz? bar) ? a : b',
+                      'foo = (baz? bar) ? a : b'
+
+      context 'when calling method on a receiver' do
+        it_behaves_like 'code with offense',
+                        'foo = (baz.foo? bar) ? a : b',
+                        'foo = (baz.foo? bar) ? a : b'
+      end
+
+      context 'when calling method with multiple arguments' do
+        it_behaves_like 'code with offense',
+                        'foo = (baz.foo? bar, baz) ? a : b',
+                        'foo = (baz.foo? bar, baz) ? a : b'
+      end
+    end
   end
 
   context 'when `RedundantParenthesis` would cause an infinite loop' do