Implement no args Struct.new constructor in Ruby 3.3

[simonlevasseur]

Ruby 3.3 introduces a new 0 args constructor for Struct. This PR implements that compatibility in Truffleruby.

[andrykonchin]

It doesn't seem a correct change. And adding more specs would catch the issue.

Optional parameter will always consume the first argument and will be nil only if there are no positional arguments at all. But it isn't how it's supposed to work:

Struct.new(:foo, :bar).name # => nil

Handling the first argument (if any) depends on its type. Non-Symbol argument will be handled as a class name. A Symbol argument - as a member name.

So it's more like:

if klass_name.is_a?(Symbol)
  attrs.unshift(klass_name)
  klass_name = nil
end

[nirvdrum]

Thanks. We'll add more specs and fix this.

[nirvdrum]

@andrykonchin I took another look at this and I'm a little confused. The code appears to already do what you suggest with regards to checking if the first argument is a Symbol and I couldn't see a behavioral difference in the Struct.new(:foo, :bar).name example. Can you please elaborate on what the problem is?

[eregon]

I'm not sure exactly what Andrii meant but the current logic + optional argument makes it really hard to reason about.

Optional + rest arguments seems quite difficult to follow, how about def self.new(*attrs, keyword_init: nil, &block) and then below check if attrs.first is a Symbol (if so it's an attribute, so nothing special to do, if not try StringValue and if that succeeds use it as the name and .shift).
Another advantage of that is the common case by far is no klass_name, so then we avoid an extra unshift for that case + make the logic clearer.

[andrykonchin]

Oh, my bad. Sorry for such delaying. The PR will be merged ASAP.