From 695710e3a28e68fa9688934a6d20aea9232de73a Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Sat, 28 Nov 2020 17:13:22 +0900
Subject: [PATCH] Fix a false positive for
 `Style/MethodCallWithoutArgsParentheses`

This PR fixes the following false positive for `Style/MethodCallWithoutArgsParentheses`
when assigning to a default argument with the same name.

```console
% cat example.rb
def foo(test = test())
end

% ruby -c example.rb
Syntax OK

% rubocop --only Style/MethodCallWithoutArgsParentheses -a example.rb
Inspecting 1 file
C

Offenses:

example.rb:1:20: C: [Corrected] Style/MethodCallWithoutArgsParentheses:
Do not use parentheses for method calls with no arguments.
def foo(test = test())
                   ^^

1 file inspected, 1 offense detected, 1 offense corrected

% cat example.rb
def foo(test = test)
end

% ruby -c example.rb
example.rb:1: circular argument reference - test
```

It prevents `example.rb:1: circular argument reference - test`.
---
 ...tive_for_method_call_without_args_parentheses.md |  1 +
 .../style/method_call_without_args_parentheses.rb   | 13 +++++++++++--
 .../method_call_without_args_parentheses_spec.rb    |  7 +++++++
 3 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 changelog/fix_false_positive_for_method_call_without_args_parentheses.md

diff --git a/changelog/fix_false_positive_for_method_call_without_args_parentheses.md b/changelog/fix_false_positive_for_method_call_without_args_parentheses.md
new file mode 100644
index 00000000000..5e3d265ab15
--- /dev/null
+++ b/changelog/fix_false_positive_for_method_call_without_args_parentheses.md
@@ -0,0 +1 @@
+* [#9113](https://github.com/rubocop-hq/rubocop/pull/9113): Fix a false positive for `Style/MethodCallWithoutArgsParentheses` when assigning to a default argument with the same name. ([@koic][])
diff --git a/lib/rubocop/cop/style/method_call_without_args_parentheses.rb b/lib/rubocop/cop/style/method_call_without_args_parentheses.rb
index f27500c34b1..fb1e0351484 100644
--- a/lib/rubocop/cop/style/method_call_without_args_parentheses.rb
+++ b/lib/rubocop/cop/style/method_call_without_args_parentheses.rb
@@ -21,21 +21,30 @@ class MethodCallWithoutArgsParentheses < Base
         def on_send(node)
           return unless !node.arguments? && node.parenthesized?
           return if ineligible_node?(node)
+          return if default_argument?(node)
           return if ignored_method?(node.method_name)
           return if same_name_assignment?(node)
 
+          register_offense(node)
+        end
+
+        private
+
+        def register_offense(node)
           add_offense(offense_range(node)) do |corrector|
             corrector.remove(node.loc.begin)
             corrector.remove(node.loc.end)
           end
         end
 
-        private
-
         def ineligible_node?(node)
           node.camel_case_method? || node.implicit_call? || node.prefix_not?
         end
 
+        def default_argument?(node)
+          node.parent&.optarg_type?
+        end
+
         def same_name_assignment?(node)
           any_assignment?(node) do |asgn_node|
             next variable_in_mass_assignment?(node.method_name, asgn_node) if asgn_node.masgn_type?
diff --git a/spec/rubocop/cop/style/method_call_without_args_parentheses_spec.rb b/spec/rubocop/cop/style/method_call_without_args_parentheses_spec.rb
index 345a4e1e9ab..6646d55a41a 100644
--- a/spec/rubocop/cop/style/method_call_without_args_parentheses_spec.rb
+++ b/spec/rubocop/cop/style/method_call_without_args_parentheses_spec.rb
@@ -56,6 +56,13 @@
       expect_no_offenses('test = test()')
     end
 
+    it 'accepts parens in default argument assignment' do
+      expect_no_offenses(<<~RUBY)
+        def foo(test = test())
+        end
+      RUBY
+    end
+
     it 'accepts parens in shorthand assignment' do
       expect_no_offenses('test ||= test()')
     end