Rubocop converting single-line methods to Endless methods on unsupported Rubies

[searls]

Noticed this while updating Standard to support 1.8.1, but verified in this repro repo that it persists in 1.9.0 as well

Expected behavior

When running on Rubies older than 3.0, I'd expect Rubocop's defaults to not change code into endless methods, as they won't be valid Ruby.

Given:

echo "def Foo;'hi'end" | bundle exec rubocop -a -s wat.rb

I'd expect it to correct to:

====================
def Foo
  'hi'
end

Actual behavior

In fact, it looks like Rubocop is doing a first-pass and converting it to an endless method, then blowing up because it's not parseable. Full output follows:

For /Users/justin/tmp/wat: Default configuration from /Users/justin/.rbenv/versions/2.4.10/lib/ruby/gems/2.4.0/gems/rubocop-1.9.0/config/default.yml
Inspecting 1 file
Scanning /Users/justin/tmp/wat/wat.rb
E

Offenses:

wat.rb:1:1: C: [Corrected] Style/SingleLineMethods: Avoid single-line method definitions.
def Foo;'hi'end
^^^^^^^^^^^^^^^
wat.rb:1:8: C: [Corrected] Layout/SpaceAfterSemicolon: Space missing after semicolon.
def Foo;'hi'end
       ^
wat.rb:1:11: E: Lint/Syntax: unexpected token tEQL
(Using Ruby 2.4 parser; configure using TargetRubyVersion parameter, under AllCops)
def Foo() = 'hi'
          ^

1 file inspected, 3 offenses detected, 2 offenses corrected
====================
def Foo() = 'hi'
Finished in 0.14265999989584088 seconds

Steps to reproduce the problem

Here's a repro repo: https://github.com/searls/rubocop-endless-method-repro#rubocop-and-endless-methods

RuboCop version

Tested under Ruby 2.4 and 2.7 FWIW

$ [bundle exec] rubocop -V
1.9.0 (using Parser 3.0.0.0, rubocop-ast 1.4.1, running on ruby 2.7.2 x86_64-darwin20)

[rrosenblum]

Sounds like we need to add a check for the Ruby version before handling anything with endless methods. A quick look into the code, Style/EndlessMethod appears to have a check for Ruby 3.0. This issue seems to be coming from Style/SingleLineMethods because that cop supports auto-correct to endless methods. Style/SingleLineMethods is checking the config from Style/EndlessMethod, however it doesn't seem to pickup on the minimum Ruby version.

As a quick workaround, it looks like you can either disable Style/EndlessMethod or set its EnforcedStyle to disallow to prevent Style/SingleLineMethods from correcting the code to an endless method

[searls]

Thanks for digging in @rrosenblum

[dvandersluis]

Thanks @searls I overlooked this will fix shortly.

[searls]

Holy cow, @dvandersluis -- what incredible turnaround time. Thank you!! ✨

[dvandersluis]

Happy to, thanks for the bug report!