Crystal: Question method on member with value 0 in enum with flags attribute broken

[petoem]

Code:

@[Flags]
enum Animal
  UNKNOWN = 0
  DOG
  CAT
  LAMA
end

pp Animal::UNKNOWN.unknown? # => false

https://play.crystal-lang.org/#/r/5wi8

[j8r]

Why do you use @[Flags]?

[petoem]

@j8r This is just an example.
I came across it when I wanted to rename "None" to something else.
Ideally, a None member should only be created if there is no other member with a value of 0 and the member with a value of 0 should get the right question method using #== instead of #includes?.

Currently only the None member gets the right question method defined through define_enum_none_question_method.
https://github.com/crystal-lang/crystal/blob/5502b00c9482b20ed872ea0583a5fe90d91b1e84/src/compiler/crystal/semantic/top_level_visitor.cr#L698

And another effect of having None member always defined is this:
```crystal
pp Animal::UNKNOWN # => None

[petoem]

Fun fact, a None member is only created if there is no one.
https://github.com/crystal-lang/crystal/blob/5502b00c9482b20ed872ea0583a5fe90d91b1e84/src/compiler/crystal/semantic/top_level_visitor.cr#L585-L591

But this means if I define a None = 0 member, no functioning question method is created.

@[Flags]
enum Animal
  None = 0
  DOG
  CAT
  LAMA
end

pp Animal::None.none? # => false

https://play.crystal-lang.org/#/r/5wjq

[asterite]

I still think we should remove the autogenerated None and All enum members.

[petoem]

Whether we keep them or not, does not change the fact that we need to define the right question method for a member with a value of 0.

[asterite]

@petoem It's failing right now because there's special logic in Enum#includes? and Enum#each to deal with None and All. If we remove those generated enum members the issue will be trivially fixed.

[petoem]

Yeah, for example replacing this ...
https://github.com/crystal-lang/crystal/blob/fcfb8f71db6c49254f821e7346797b5499af8173/src/compiler/crystal/semantic/top_level_visitor.cr#L663
with this ...

if is_flags && counter == 0
  define_enum_question_method(enum_type, member, false)
else
  define_enum_question_method(enum_type, member, is_flags)
end

... should define the correct question method.