Add new Lint/ToEnumArguments cop

[fatkodima]

Closes #7753

This cop ensures that to_enum/enum_for, called for the current method, has correct arguments.

# bad
def method(x, y = 1)
  return to_enum(__method__, x) # `y` is missing
end
      
# good
def method(x, y = 1)
  return to_enum(__method__, x, y)
end

I have made this mistake myself 😄 - proof

[bbatsov]

I don't think I've ever used those methods, so I'll leave it to the others to provide feedback for that cop. Some more rationale might be useful, as others like me might first think this is something about enumerations. :D

[marcandre]

Good cop! I've made this kind of mistake a few times.

Need to get to bed, just checked the tests, looks good, I'd be even stricter.

[marcandre]

Also, could you support forwarding please? (..., Ruby 2.7+)

[fatkodima]

Did you mean something like

def meth(...)
  return to_enum(...) unless block_given?
end

Is there a usecase for this?

It does not make much sense to me, compared to

def meth(...)
  return to_enum(:meth, ...) unless block_given?
end

which is an invalid syntax, unfortunately.

Also, currently the first example passes without violation.

[marcandre]

It does not make much sense to me, compared to

def meth(...)
  return to_enum(:meth, ...) unless block_given?
end

This is what I meant, and it is Ruby 3.0+ only, my bad. Still would be nice to do (maybe just missing a test)

[fatkodima]

Added a TODO for the future, as it is easy to implement, but hard to test before 3.0 is released.

[marcandre]

Added a TODO for the future, as it is easy to implement, but hard to test before 3.0 is released.

As you wish. FYI, we already run our CI against ruby-head, and testing locally is easy with rvm install ruby-head.

[marcandre]

@bbatsov ok to merge?

[bbatsov]

Yep.

[bquorning]

I am not sure I completely understand this cop. I am not sure that the following code should be flagged:

def foo
  bar = to_enum(:baz).count
  bar > 42
end

Is it a bug, or have I just misunderstood this cop?