Deprecate iterator? method

[Feature #15547] [Fix GH-2071]

spec/ruby/core/kernel/iterator_spec.rb

@@ -1,6 +1,7 @@
 require_relative '../../spec_helper'
 require_relative 'fixtures/classes'
 
+ruby_version_is ""..."2.8" do
   describe "Kernel#iterator?" do
     it "is a private method" do
       Kernel.should have_private_instance_method(:iterator?)
@@ -10,3 +11,4 @@ end
   describe "Kernel.iterator?" do
     it "needs to be reviewed for spec completeness"
   end
+end

vm_eval.c

@@ -2312,7 +2312,6 @@ rb_f_local_variables(VALUE _)
 /*
  *  call-seq:
  *     block_given?   -> true or false
- *     iterator?      -> true or false
  *
  *  Returns <code>true</code> if <code>yield</code> would execute a
  *  block in the current context. The <code>iterator?</code> form
@@ -2330,7 +2329,6 @@ rb_f_local_variables(VALUE _)
  *     try do "hello" end   #=> "hello"
  */
 
-
 static VALUE
 rb_f_block_given_p(VALUE _)
 {
@@ -2346,6 +2344,20 @@ rb_f_block_given_p(VALUE _)
     }
 }
 
+/*
+ *  call-seq:
+ *     iterator?      -> true or false
+ *
+ *  Deprecated.  Use block_given? instead.
+ */
+
+static VALUE
+rb_f_iterator_p(VALUE self)
+{
+    rb_warn_deprecated("iterator?", "block_given?");
+    return rb_f_block_given_p(self);
+}
+
 VALUE
 rb_current_realfilepath(void)
 {
@@ -2361,7 +2373,7 @@ Init_vm_eval(void)
 {
     rb_define_global_function("eval", rb_f_eval, -1);
     rb_define_global_function("local_variables", rb_f_local_variables, 0);
-    rb_define_global_function("iterator?", rb_f_block_given_p, 0);
+    rb_define_global_function("iterator?", rb_f_iterator_p, 0);
     rb_define_global_function("block_given?", rb_f_block_given_p, 0);
 
     rb_define_global_function("catch", rb_f_catch, -1);