Fix an incorrect auto-correct for Style/SingleLineMethods

This PR fixes an incorrect auto-correct for `Style/SingleLineMethods`
when using `return`, `break`, or `next` for one line method body in Ruby 3.0.

These are not supported in the endless method definition.

```console
% ruby -v
ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-darwin19]

% cat example.rb
def foo(argument) break bar(argument); end
def foo(argument) next bar(argument); end
def foo(argument) return bar(argument); end

% ruby -c example.rb
Syntax OK

% bundle exec rubocop --only Style/SingleLineMethods -a
(snip)

Inspecting 1 file
C

Offenses:

example.rb:1:1: C: [Corrected] Style/SingleLineMethods: Avoid
single-line method definitions.
def foo(argument) break bar(argument); end
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
example.rb:2:1: C: [Corrected] Style/SingleLineMethods: Avoid
single-line method definitions.
def foo(argument) next bar(argument); end
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
example.rb:3:1: C: [Corrected] Style/SingleLineMethods: Avoid
single-line method definitions.
def foo(argument) return bar(argument); end
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 3 offenses detected, 3 offenses corrected

% cat example.rb
def foo(argument) = break bar(argument)
def foo(argument) = next bar(argument)
def foo(argument) = return bar(argument)

% ruby -ce 'def foo(argument) = break bar(argument)'
-e:1: syntax error, unexpected local variable or method, expecting
end-of-input
def foo(argument) = break bar(argument)

% ruby -ce 'def foo(argument) = next bar(argument)'
-e:1: syntax error, unexpected local variable or method, expecting
end-of-input
def foo(argument) = next bar(argument)

% ruby -ce 'def foo(argument) = return bar(argument)'
-e:1: syntax error, unexpected local variable or method, expecting
end-of-input
def foo(argument) = return bar(argument)
```

changelog/fix_incorrect_autocorrect_for_style_single_line_methods.md

@@ -0,0 +1 @@
+* [#9909](https://github.com/rubocop/rubocop/pull/9909): This PR fixes an incorrect auto-correct for `Style/SingleLineMethods` when using `return`, `break`, or `next` for one line method body in Ruby 3.0. ([@koic][])

lib/rubocop/cop/style/single_line_methods.rb

@@ -36,6 +36,7 @@ class SingleLineMethods < Base
         extend AutoCorrector
 
         MSG = 'Avoid single-line method definitions.'
+        NOT_SUPPORTED_ENDLESS_METHOD_BODY_TYPES = %i[return break next].freeze
 
         def on_def(node)
           return unless node.single_line?
@@ -62,13 +63,10 @@ def allow_empty?
 
         def correct_to_endless?(body_node)
           return false if target_ruby_version < 3.0
-
-          endless_method_config = config.for_cop('Style/EndlessMethod')
-
-          return false unless endless_method_config['Enabled']
-          return false if endless_method_config['EnforcedStyle'] == 'disallow'
+          return false if disallow_endless_method_style?
           return false unless body_node
-          return false if body_node.parent.assignment_method?
+          return false if body_node.parent.assignment_method? ||
+                          NOT_SUPPORTED_ENDLESS_METHOD_BODY_TYPES.include?(body_node.type)
 
           !(body_node.begin_type? || body_node.kwbegin_type?)
         end
@@ -129,6 +127,13 @@ def method_body_source(method_body)
         def require_parentheses?(method_body)
           method_body.send_type? && !method_body.arguments.empty? && !method_body.comparison_method?
         end
+
+        def disallow_endless_method_style?
+          endless_method_config = config.for_cop('Style/EndlessMethod')
+          return false unless endless_method_config['Enabled']
+
+          endless_method_config['EnforcedStyle'] == 'disallow'
+        end
       end
     end
   end

spec/rubocop/cop/style/single_line_methods_spec.rb

@@ -219,6 +219,30 @@ def #{op}(other) = self #{op} other
         end
       end
 
+      it 'does not to an endless class method definition when using `return`' do
+        expect_correction(<<~RUBY.strip, source: 'def foo(argument) return bar(argument); end')
+          def foo(argument)#{trailing_whitespace}
+            return bar(argument);#{trailing_whitespace}
+          end
+        RUBY
+      end
+
+      it 'does not to an endless class method definition when using `break`' do
+        expect_correction(<<~RUBY.strip, source: 'def foo(argument) break bar(argument); end')
+          def foo(argument)#{trailing_whitespace}
+            break bar(argument);#{trailing_whitespace}
+          end
+        RUBY
+      end
+
+      it 'does not to an endless class method definition when using `next`' do
+        expect_correction(<<~RUBY.strip, source: 'def foo(argument) next bar(argument); end')
+          def foo(argument)#{trailing_whitespace}
+            next bar(argument);#{trailing_whitespace}
+          end
+        RUBY
+      end
+
       # NOTE: Setter method cannot be defined in the endless method definition.
       it 'corrects to multiline method definition when defining setter method' do
         expect_correction(<<~RUBY.chop, source: 'def foo=(foo) @foo = foo end')