[Bug #20325] `Enumerator.product.size` is 0 if any size is 0

enumerator.c

@@ -3536,10 +3536,19 @@ static VALUE
 enum_product_total_size(VALUE enums)
 {
     VALUE total = INT2FIX(1);
+    VALUE sizes = rb_ary_hidden_new(RARRAY_LEN(enums));
     long i;
 
     for (i = 0; i < RARRAY_LEN(enums); i++) {
         VALUE size = enum_size(RARRAY_AREF(enums, i));
+        if (size == INT2FIX(0)) {
+            rb_ary_resize(sizes, 0);
+            return size;
+        }
+        rb_ary_push(sizes, size);
+    }
+    for (i = 0; i < RARRAY_LEN(sizes); i++) {
+        VALUE size = RARRAY_AREF(sizes, i);
 
         if (NIL_P(size) || (RB_TYPE_P(size, T_FLOAT) && isinf(NUM2DBL(size)))) {
             return size;

test/ruby/test_enumerator.rb

@@ -953,11 +953,7 @@ class TestEnumerator < Test::Unit::TestCase
     assert_equal(true, e.is_lambda)
   end
 
-  def test_product
-    ##
-    ## Enumerator::Product
-    ##
-
+  def test_product_new
     # 0-dimensional
     e = Enumerator::Product.new
     assert_instance_of(Enumerator::Product, e)
@@ -994,15 +990,16 @@ class TestEnumerator < Test::Unit::TestCase
     e.each { |x,| heads << x }
     assert_equal [1, 1, 2, 2, 3, 3], heads
 
+    # Any enumerable is 0 size
+    assert_equal(0, Enumerator::Product.new([], 1..).size)
+
     # Reject keyword arguments
     assert_raise(ArgumentError) {
       Enumerator::Product.new(1..3, foo: 1, bar: 2)
     }
+  end
 
-    ##
-    ## Enumerator.product
-    ##
-
+  def test_s_product
     # without a block
     e = Enumerator.product(1..3, %w[a b])
     assert_instance_of(Enumerator::Product, e)
@@ -1029,6 +1026,8 @@ class TestEnumerator < Test::Unit::TestCase
     assert_equal(nil, e.size)
     assert_equal [[1, "a"], [1, "b"], [2, "a"], [2, "b"]], e.take(4)
 
+    assert_equal(0, Enumerator.product([], 1..).size)
+
     # Reject keyword arguments
     assert_raise(ArgumentError) {
       Enumerator.product(1..3, foo: 1, bar: 2)