2 files changed, 73 insertions, 0 deletions

diff --git a/hash.c b/hash.c
index 1d97ccadd3..85bcda3c73 100644
--- a/hash.c
+++ b/hash.c
@@ -1861,6 +1861,52 @@ rb_hash_s_try_convert(VALUE dummy, VALUE hash)
     return rb_check_hash_type(hash);
 }
 
+/*
+ *  call-seq:
+ *     Hash.ruby2_keywords_hash?(hash) -> true or false
+ *
+ *  Checks if a given hash is flagged by Module#ruby2_keywords (or
+ *  Proc#ruby2_keywords).
+ *  This method is not for casual use; debugging, researching, and
+ *  some truly necessary cases like serialization of arguments.
+ *
+ *     ruby2_keywords def foo(*args)
+ *       Hash.ruby2_keywords_hash?(args.last)
+ *     end
+ *     foo(k: 1)   #=> true
+ *     foo({k: 1}) #=> false
+ */
+static VALUE
+rb_hash_s_ruby2_keywords_hash_p(VALUE dummy, VALUE hash)
+{
+    Check_Type(hash, T_HASH);
+    return (RHASH(hash)->basic.flags & RHASH_PASS_AS_KEYWORDS) ? Qtrue : Qfalse;
+}
+
+/*
+ *  call-seq:
+ *     Hash.ruby2_keywords_hash(hash) -> hash
+ *
+ *  Duplicates a given hash and adds a ruby2_keywords flag.
+ *  This method is not for casual use; debugging, researching, and
+ *  some truly necessary cases like deserialization of arguments.
+ *
+ *     h = {k: 1}
+ *     h = Hash.ruby2_keywords_hash(h)
+ *     def foo(k: 42)
+ *       k
+ *     end
+ *     foo(*[h]) #=> 1 with neither a warning or an error
+ */
+static VALUE
+rb_hash_s_ruby2_keywords_hash(VALUE dummy, VALUE hash)
+{
+    Check_Type(hash, T_HASH);
+    hash = rb_hash_dup(hash);
+    RHASH(hash)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
+    return hash;
+}
+
 struct rehash_arg {
     VALUE hash;
     st_table *tbl;
@@ -6339,6 +6385,9 @@ Init_Hash(void)
 
     rb_define_method(rb_cHash, "deconstruct_keys", rb_hash_deconstruct_keys, 1);
 
+    rb_define_singleton_method(rb_cHash, "ruby2_keywords_hash?", rb_hash_s_ruby2_keywords_hash_p, 1);
+    rb_define_singleton_method(rb_cHash, "ruby2_keywords_hash", rb_hash_s_ruby2_keywords_hash, 1);
+
     /* Document-class: ENV
      *
      * ENV is a hash-like accessor for environment variables.
diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index ccc3355930..304bd585a4 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -1740,4 +1740,28 @@ class TestHash < Test::Unit::TestCase
       super
     end
   end
+
+  ruby2_keywords def get_flagged_hash(*args)
+    args.last
+  end
+
+  def check_flagged_hash(k: :NG)
+    k
+  end
+
+  def test_ruby2_keywords_hash?
+    flagged_hash = get_flagged_hash(k: 1)
+    assert_equal(true, Hash.ruby2_keywords_hash?(flagged_hash))
+    assert_equal(false, Hash.ruby2_keywords_hash?({}))
+    assert_raise(TypeError) { Hash.ruby2_keywords_hash?(1) }
+  end
+
+  def test_ruby2_keywords_hash!
+    hash = {k: 1}
+    assert_equal(false, Hash.ruby2_keywords_hash?(hash))
+    hash = Hash.ruby2_keywords_hash(hash)
+    assert_equal(true, Hash.ruby2_keywords_hash?(hash))
+    assert_equal(1, check_flagged_hash(*[hash]))
+    assert_raise(TypeError) { Hash.ruby2_keywords_hash(1) }
+  end
 end