Incompatible Struct#initialize with mixed keyword args

[nevans]

It looks like TruffleRuby behaves differently when a Struct is initialized with both positional and keyword args.

Here's a test script to demonstrate:

#!/usr/bin/env ruby

puts ?=*72
puts "Ruby Engine:   #{RUBY_ENGINE} #{RUBY_ENGINE_VERSION}"

Test = Struct.new(:foo, :attr)
puts "  Keywords:   %p" % [Test.new(foo: "foo", attr: {"bar" => "baz"})]
puts "  Positional: %p" % [Test.new("foo", {"bar" => "baz"})]
puts "  Mixed:      %p" % [Test.new("foo", "bar" => "baz")]
puts "  Mixed (2):  %p" % [Test.new("foo", attr: {"bar" => "baz"})]
puts "  Mixed (3):  %p" % [Test.new("foo", attr: {weird: true}, "bar" => "baz")]

__END__
$ ruby test.rb && RBENV_VERSION=truffleruby-24.2.1 ruby test.rb
========================================================================
Ruby Engine:   ruby 3.4.2
  Keywords:   #<struct Test foo="foo", attr={"bar" => "baz"}>
  Positional: #<struct Test foo="foo", attr={"bar" => "baz"}>
  Mixed:      #<struct Test foo="foo", attr={"bar" => "baz"}>
  Mixed (2):  #<struct Test foo="foo", attr={attr: {"bar" => "baz"}}>
  Mixed (3):  #<struct Test foo="foo", attr={attr: {weird: true}, "bar" => "baz"}>
========================================================================
Ruby Engine:   truffleruby 24.2.1
  Keywords:   #<struct Test foo="foo", attr={"bar"=>"baz"}>
  Positional: #<struct Test foo="foo", attr={"bar"=>"baz"}>
  Mixed:      #<struct Test foo="foo", attr=nil>
  Mixed (2):  #<struct Test foo="foo", attr=nil>
  Mixed (3):  #<struct Test foo="foo", attr=nil>

[andrykonchin]

Thank you for the report, we'll look into it.

[eregon]

We're fixing this. As a note, it's best to never do that in real code though, as it's really an edge that is I believe not supposed to be used, notably because it behaves inconsistently when there is 0 or 1+ positional arguments, as your 1st and 4th examples show.
IOW, since Struct#new accepts keyword arguments (except with Struct.new(..., keyword_init: false)), it should only be given keyword arguments when passing no positional arguments, otherwise it's unclear and confusing how these keyword arguments are treated.

[andrykonchin]

Fixed in a227095

[nevans]

As a note, it's best to never do that in real code though

Agreed. I think the code that triggered this may have been originally written prior to ruby 3.0 and the many keyword arguments changes. (I don't actually recall offhand what triggered it... but I think it was also only in the tests.)