Handle positional or keywords args for Struct without keyword_init: true

CHANGELOG.md

@@ -39,6 +39,7 @@ Compatibility:
 * Fix `Coverage.supported?` and raise `TypeError` if argument is not Symbol (#3039, @andrykonchin).
 * Accept options argument to `Regexp.{new,compile}` of String and warn for unknown types (#3039, @rwstauner).
 * Implement `Time#deconstruct_keys` from Ruby 3.2 (#3039, @rwstauner).
+* Handle either positional or keywords arguments by default in `Struct.new` (#3039, @rwstauner).
 
 Performance:
 

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

@@ -56,7 +56,8 @@ def self.new(klass_name, *attrs, keyword_init: nil, &block)
     end
 
     klass = Class.new self do
-      _specialize attrs unless keyword_init
+      # _specialize doesn't support keyword arguments
+      _specialize attrs if Primitive.false?(keyword_init)
 
       attrs.each do |a|
         define_method(a) { Primitive.object_hidden_var_get(self, a) }
@@ -71,6 +72,7 @@ def self.[](*args)
         new(*args)
       end
 
+      # This doesn't apply when keyword_init is nil.
       if keyword_init
         def self.inspect
           super + '(keyword_init: true)'
@@ -156,7 +158,13 @@ def initialize(*args, **kwargs)
       raise ArgumentError, "Expected #{attrs.size}, got #{args.size}"
     end
 
-    if Primitive.class(self)::KEYWORD_INIT
+    keyword_init = Primitive.class(self)::KEYWORD_INIT
+
+    # When keyword_init is nil:
+    #   If there are any positional args we treat them all as positional.
+    #   If there are no args at all we also want to run the positional handling code.
+
+    if keyword_init || (Primitive.nil?(keyword_init) && args.empty? && !kwargs.empty?)
       # Accept a single positional hash for https://bugs.ruby-lang.org/issues/18632 and spec
       if kwargs.empty? && args.size == 1 && Primitive.is_a?(args.first, Hash)
         kwargs = args.first