Revert the default size of Enumerator::Producer to infinity

[Bug #21780]

Author: knu

NEWS.md

@@ -38,8 +38,8 @@ Note: We're only listing outstanding class updates.
     * `Enumerator.produce` now accepts an optional `size` keyword argument
       to specify the size of the enumerator.  It can be an integer,
       `Float::INFINITY`, a callable object (such as a lambda), or `nil` to
-      indicate unknown size.  When not specified, the size is unknown (`nil`).
-      Previously, the size was always `Float::INFINITY` and not specifiable.
+      indicate unknown size.  When not specified, the size defaults to
+      `Float::INFINITY`.
 
         ```ruby
         # Infinite enumerator

enumerator.c

@@ -3037,7 +3037,8 @@ producer_size(VALUE obj, VALUE args, VALUE eobj)
  * The optional +size+ keyword argument specifies the size of the enumerator,
  * which can be retrieved by Enumerator#size.  It can be an integer,
  * +Float::INFINITY+, a callable object (such as a lambda), or +nil+ to
- * indicate unknown size.  When not specified, the size is unknown (+nil+).
+ * indicate unknown size.  When not specified, the size defaults to
+ * +Float::INFINITY+.
  *
  *   # Infinite enumerator
  *   enum = Enumerator.produce(1, size: Float::INFINITY, &:succ)
@@ -3063,7 +3064,7 @@ enumerator_s_produce(int argc, VALUE *argv, VALUE klass)
     rb_scan_args_kw(RB_SCAN_ARGS_LAST_HASH_KEYWORDS, argc, argv, "01:", &init, &opts);
     rb_get_kwargs(opts, keyword_ids, 0, 1, &size);
 
-    size = UNDEF_P(size) ? Qnil : convert_to_feasible_size_value(size);
+    size = UNDEF_P(size) ? DBL2NUM(HUGE_VAL) : convert_to_feasible_size_value(size);
 
     if (argc == 0 || (argc == 1 && !NIL_P(opts))) {
         init = Qundef;

test/ruby/test_enumerator.rb

@@ -892,22 +892,22 @@ def test_produce
     passed_args = []
     enum = Enumerator.produce { |obj| passed_args << obj; (obj || 0).succ }
     assert_instance_of(Enumerator, enum)
-    assert_nil enum.size
+    assert_equal Float::INFINITY, enum.size
     assert_equal [1, 2, 3], enum.take(3)
     assert_equal [nil, 1, 2], passed_args
 
     # With initial object
     passed_args = []
     enum = Enumerator.produce(1) { |obj| passed_args << obj; obj.succ }
     assert_instance_of(Enumerator, enum)
-    assert_nil enum.size
+    assert_equal Float::INFINITY, enum.size
     assert_equal [1, 2, 3], enum.take(3)
     assert_equal [1, 2], passed_args
 
     # Raising StopIteration
     words = "The quick brown fox jumps over the lazy dog.".scan(/\w+/)
     enum = Enumerator.produce { words.shift or raise StopIteration }
-    assert_nil enum.size
+    assert_equal Float::INFINITY, enum.size
     assert_instance_of(Enumerator, enum)
     assert_equal %w[The quick brown fox jumps over the lazy dog], enum.to_a
 
@@ -917,7 +917,7 @@ def test_produce
       obj.respond_to?(:first) or raise StopIteration
       obj.first
     }
-    assert_nil enum.size
+    assert_equal Float::INFINITY, enum.size
     assert_instance_of(Enumerator, enum)
     assert_nothing_raised {
       assert_equal [