From b1778dd5e6830f3ef758aaae26b71ee06f274c55 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Fri, 18 Feb 2022 02:00:32 +0900
Subject: [PATCH] [Fix #10421] Make `Style/DefWithParentheses` aware of endless
 method definition

Fixes #10421.

This PR makes `Style/DefWithParentheses` aware of endless method definition.

`def foo() do_something end` will continue to allow because `def foo do_something end`
is a syntax error.
On the other hand, be aware that the endless method definition's parentheses can be omitted.
---
 ...eses_aware_of_endless_method_definition.md |  1 +
 lib/rubocop/cop/style/def_with_parentheses.rb | 20 ++++++++++++-------
 .../cop/style/def_with_parentheses_spec.rb    | 13 ++++++++++++
 3 files changed, 27 insertions(+), 7 deletions(-)
 create mode 100644 changelog/fix_make_style_def_with_parentheses_aware_of_endless_method_definition.md

diff --git a/changelog/fix_make_style_def_with_parentheses_aware_of_endless_method_definition.md b/changelog/fix_make_style_def_with_parentheses_aware_of_endless_method_definition.md
new file mode 100644
index 00000000000..51cdef326a3
--- /dev/null
+++ b/changelog/fix_make_style_def_with_parentheses_aware_of_endless_method_definition.md
@@ -0,0 +1 @@
+* [#10421](https://github.com/rubocop/rubocop/issues/10421): Make `Style/DefWithParentheses` aware of endless method definition. ([@koic][])
diff --git a/lib/rubocop/cop/style/def_with_parentheses.rb b/lib/rubocop/cop/style/def_with_parentheses.rb
index 7a3c43f4830..0f502b63cd3 100644
--- a/lib/rubocop/cop/style/def_with_parentheses.rb
+++ b/lib/rubocop/cop/style/def_with_parentheses.rb
@@ -11,27 +11,33 @@ module Style
       #
       #   # bad
       #   def foo()
-      #     # does a thing
+      #     do_something
       #   end
       #
       #   # good
       #   def foo
-      #     # does a thing
+      #     do_something
       #   end
       #
-      #   # also good
-      #   def foo() does_a_thing end
+      #   # bad
+      #   def foo() = do_something
+      #
+      #   # good
+      #   def foo = do_something
+      #
+      #   # good (without parentheses it's a syntax error)
+      #   def foo() do_something end
       #
       # @example
       #
       #   # bad
       #   def Baz.foo()
-      #     # does a thing
+      #     do_something
       #   end
       #
       #   # good
       #   def Baz.foo
-      #     # does a thing
+      #     do_something
       #   end
       class DefWithParentheses < Base
         extend AutoCorrector
@@ -39,7 +45,7 @@ class DefWithParentheses < Base
         MSG = "Omit the parentheses in defs when the method doesn't accept any arguments."
 
         def on_def(node)
-          return if node.single_line?
+          return if node.single_line? && !node.endless?
           return unless !node.arguments? && (node_arguments = node.arguments.source_range)
 
           add_offense(node_arguments) do |corrector|
diff --git a/spec/rubocop/cop/style/def_with_parentheses_spec.rb b/spec/rubocop/cop/style/def_with_parentheses_spec.rb
index 52ffe16bbc0..51ae86d61d5 100644
--- a/spec/rubocop/cop/style/def_with_parentheses_spec.rb
+++ b/spec/rubocop/cop/style/def_with_parentheses_spec.rb
@@ -29,6 +29,19 @@ def Test.func
     RUBY
   end
 
+  context 'Ruby >= 3.0', :ruby30 do
+    it 'reports an offense for endless method definition with empty parens' do
+      expect_offense(<<~RUBY)
+        def foo() = do_something
+               ^^ Omit the parentheses in defs when the method doesn't accept any arguments.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        def foo = do_something
+      RUBY
+    end
+  end
+
   it 'accepts def with arg and parens' do
     expect_no_offenses(<<~RUBY)
       def func(a)