array.c: return first unique element in Array#uniq

* array.c (ary_add_hash): Fix consistency issue between Array#uniq and
  Array#uniq! [Bug ruby#9340] [ruby-core:59457]
* test/ruby/test_array.rb (class TestArray): regression test for above.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44512 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Conflicts:
	ChangeLog

Author: tmm1

array.c

@@ -3904,7 +3904,9 @@ ary_add_hash(VALUE hash, VALUE ary)
 
     for (i=0; i<RARRAY_LEN(ary); i++) {
 	VALUE elt = RARRAY_AREF(ary, i);
-	rb_hash_aset(hash, elt, elt);
+	if (rb_hash_lookup2(hash, elt, Qundef) == Qundef) {
+	    rb_hash_aset(hash, elt, elt);
+	}
     }
     return hash;
 }

test/ruby/test_array.rb

@@ -1524,6 +1524,11 @@ def test_uniq
     assert(a.none?(&:frozen?))
     assert_equal(%w(a), b)
     assert(b.none?(&:frozen?))
+
+    bug9340 = "[ruby-core:59457]"
+    ary = [bug9340, bug9340.dup, bug9340.dup]
+    assert_equal 1, ary.uniq.size
+    assert_same bug9340, ary.uniq[0]
   end
 
   def test_uniq_with_block