Add Enumerator#product.

Author: itarato

CHANGELOG.md

@@ -29,6 +29,7 @@ Compatibility:
 * Add `Module#refinements` (#3039, @itarato).
 * Add `Refinement#refined_class` (#3039, @itarato).
 * Add `rb_hash_new_capa` function (#3039, @itarato).
+* Add `Enumerator#product` (#3039, @itarato).
 
 Performance:
 

spec/truffleruby.next-specs

@@ -34,3 +34,5 @@ spec/ruby/core/module/refinements_spec.rb
 spec/ruby/core/refinement/refined_class_spec.rb
 spec/ruby/core/module/used_refinements_spec.rb
 spec/ruby/optional/capi/hash_spec.rb
+
+spec/ruby/core/enumerator/product_spec.rb

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

@@ -231,6 +231,40 @@ def self.produce(initial = nil)
     end
   end
 
+  def self.product(*enums, **kwargs, &block)
+    Truffle::KernelOperations.validate_no_kwargs(kwargs)
+
+    return Product.new(*enums) if Primitive.nil?(block)
+    product_iterator([], enums, &block)
+  end
+
+  class << self
+    protected def product_iterator(current, rest_enums, &block)
+      return block.call(current) if rest_enums.empty?
+
+      rest_enums_tail = rest_enums[1..]
+      rest_enums.first.each_entry do |next_e|
+        product_iterator(current + [next_e], rest_enums_tail, &block)
+      end
+    end
+  end
+
+  class Product  < Enumerator
+    def initialize(*enums, **kwargs)
+      Truffle::KernelOperations.validate_no_kwargs(kwargs)
+
+      @enums = enums
+    end
+
+    def each(&block)
+      Primitive.class(self).product_iterator([], @enums, &block)
+    end
+
+    def size
+      @enums.map(&:size).reduce(1, &:*)
+    end
+  end
+
   class Yielder
     attr_accessor :memo
 

src/main/ruby/truffleruby/core/truffle/kernel_operations.rb

@@ -242,6 +242,13 @@ def self.value_frozen?(value)
       KERNEL_FROZEN.bind(value).call
     end
 
+    def self.validate_no_kwargs(kwargs)
+      return if (kwargs_size = kwargs.size) == 0
+
+      raise ArgumentError, "unknown keyword: #{kwargs.keys.first.inspect}" if kwargs_size == 1
+      raise ArgumentError, "unknown keywords: #{kwargs.keys.map(&:inspect).join(', ')}"
+    end
+
     # To get the class even if the value's class does not include `Kernel`, use `Primitive.class`.
   end
 end