Fix Parser::SyntaxError error with endless method for object equality

[bkuhlmann]

Overview

Discovered when attempting to write an endless method for object equality that I'd get a syntax error. Here's a snippet for illustration:

class Example
  def ==(other) = hash == other.hash
end

In this case, I'm using Reek to illustrate the stack dump in case it's helpful:

Reek Stack Dump

Inspecting 1 file(s):
        !!!
        Source '/Users/bkuhlmann/Engineering/Misc/snippet.rb' cannot be processed by Reek due to a syntax error in the source file.

        This is a problem that is outside of Reek's scope and should be fixed by you, the
        user, in order for Reek being able to continue.

        Things you can try:
        - Check the syntax of the problematic file
        - If the file is not in fact a Ruby file, exclude it in your .reek.yml file

        Exception message:

        #<Parser::SyntaxError: setter method cannot be defined in an endless method definition>

        Original backtrace:

        /Users/bkuhlmann/.gem/ruby/3.0.1/gems/parser-3.0.1.0/lib/parser/diagnostic/engine.rb:72:in `process'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/parser-3.0.1.0/lib/parser/base.rb:274:in `diagnostic'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/parser-3.0.1.0/lib/parser/ruby30.rb:27:in `endless_method_name'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/parser-3.0.1.0/lib/parser/ruby30.rb:5156:in `_reduce_249'
	(eval):3:in `_racc_do_parse_c'
	(eval):3:in `do_parse'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/parser-3.0.1.0/lib/parser/base.rb:190:in `parse'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/parser-3.0.1.0/lib/parser/base.rb:207:in `parse_with_comments'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/source/source_code.rb:117:in `parse'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/source/source_code.rb:53:in `syntax_tree'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/examiner.rb:116:in `syntax_tree'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/examiner.rb:120:in `examine_tree'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/examiner.rb:94:in `block in run'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/examiner.rb:104:in `wrap_exceptions'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/examiner.rb:93:in `run'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/examiner.rb:61:in `smells'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/examiner.rb:77:in `smelly?'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/report/progress_formatter.rb:43:in `progress'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/report/text_report.rb:22:in `add_examiner'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/cli/command/report_command.rb:26:in `block in populate_reporter_with_smells'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/cli/command/report_command.rb:25:in `each'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/cli/command/report_command.rb:25:in `populate_reporter_with_smells'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/cli/command/report_command.rb:17:in `execute'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/lib/reek/cli/application.rb:32:in `execute'
	/Users/bkuhlmann/.gem/ruby/3.0.1/gems/reek-6.0.3/bin/reek:12:in `<top (required)>'
	/Users/bkuhlmann/.gem/ruby/3.0.1/bin/reek:23:in `load'
	/Users/bkuhlmann/.gem/ruby/3.0.1/bin/reek:23:in `<main>'

        !!!

Steps to Recreate

You can recreate this issue quickly by saving this Ruby snippet to snippet.rb:

class Example
  def ==(other) = hash == other.hash
end

...and then you can run the following to recreate the error:

reek snippet.rb

Desired Behavior

I would like to be able to use an endless method since it's not assignment but equality that the parser is getting confused by.

Environment

rubocop -V
1.12.1 (using Parser 3.0.1.0, rubocop-ast 1.4.1, running on ruby 3.0.1 arm64-darwin20)
  - rubocop-performance 1.10.2
  - rubocop-rake 0.5.1
  - rubocop-rspec 2.2.0

gem list reek
reek (6.0.3)

[bkuhlmann]

Thanks! 🙇