added keyword_init? to classes generated by Struct.new, Ruby 3.1 support

[moste00]

As required by #2733, every class returned by Struct.new now has a keyword_init? method that returns nil if the optional argument to Struct.new of the same name was omitted, and returns true or false if that argument was provided and was truthy or falsey, respectively.

[andrykonchin]

It's common to use already defined magic singleton object undefined that is used as a default value of an optional argument.

For performance reason its value should be checked with a primitive Primitive.undefined?(obj).

[moste00]

Thanks! Using BasicObject was indeed ugly, can you expand on how to use "undefined" ? I can't do it, a literal mention of "undefined" is just a NameError.

Anyway, I noticed that CRuby considers passing "keyword_init: nil" to Struct.new as if keyword_init was omitted (i.e. keyword_init? returns nil in this case, as if keyword_init was never passed), so I had the much simpler idea to just initialize keyword_init to nil by default : every boolean test on keyword_init is unaffected because nil is falsey, but we can still distinguish the ommited case by Primitive.nil?. Much more elegant than what I had before.

[andrykonchin]

Indeed, we don't need to distinguish cases when keyword_init isn't passed and when passed nil.

Regarding undefined - it's a magic object, that is available by default only in Ruby Core library source files (and it shouldn't be available in irb, for instance). Actually it's handled magically on the parser level so it isn't declared explicitly in Ruby source code. It's widely used in the Core library:

truffleruby/src/main/ruby/truffleruby/core/io.rb

Lines 430 to 435 in 01e0ce5

	def self.foreach(name, separator=undefined, limit=undefined, **options, &block)
	return to_enum(:foreach, name, separator, limit, **options) unless block
	name = Truffle::Type.coerce_to_path name
	separator = $/ if Primitive.undefined?(separator)

[andrykonchin]

It seems simpler and shorted to me to calculate value in the keyword_init? method:

def self.keyword_init?
   return nil if Primitive.undefined?(KEYWORD_INIT) || Primitive.nil?(KEYWORD_INIT)
   KEYWORD_INIT != false
end

[andrykonchin]

Looks good to me 👍 .

minor: self::KEYWORD_INIT looks a bit shorter than self.const_get(:KEYWORD_INIT) but should work too.

[eregon]

Yes, self::KEYWORD_INIT is better, const_get is a few more indirections and less readable too.

[andrykonchin]

Probably I would add one missing spec for keyword_init: nil case.

[andrykonchin]

Extra empty line?

[eregon]

This should indented two spaces less

[andrykonchin]

Looks good to me.

There are minor formatting issues only.

[eregon]

@moste00 There is a feature freeze this Friday for truffleruby, so we need to get this PR and #2907 and #2908 merged before Friday. We will do the remaining changes (mostly style and git fixes) to make sure it's merged in time.

[eregon]

Merged in 8d6a531

[moste00]

Thank you so much for taking care of this @eregon, I greatly apologize for leaving it hanging the past week, things were a bit busy for me.