io.c: warn old write

* io.c (rb_io_puts): warn if write method accepts just one
  argument.  [ruby-core:83529] [Feature #14042]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60423 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -1690,6 +1690,13 @@ static VALUE
 rb_io_writev(VALUE io, int argc, VALUE *argv)
 {
     if (argc > 1 && rb_obj_method_arity(io, id_write) == 1) {
+	if (io != rb_stderr && RTEST(ruby_verbose)) {
+	    VALUE klass = CLASS_OF(io);
+	    char sep = FL_TEST(klass, FL_SINGLETON) ? (klass = io, '.') : '#';
+	    rb_warning("%+"PRIsVALUE"%c""write is outdated interface"
+		       " which accepts just one argument",
+		       klass, sep);
+	}
 	do rb_io_write(io, *argv++); while (--argc);
 	return argv[0];		/* unused right now */
     }

test/ruby/test_io.rb

@@ -2458,6 +2458,22 @@ End
     end)
   end
 
+  def test_puts_old_write
+    capture = String.new
+    def capture.write(str)
+      self << str
+    end
+
+    capture.clear
+    assert_warning(/[.#]write is outdated/) do
+      stdout, $stdout = $stdout, capture
+      puts "hey"
+    ensure
+      $stdout = stdout
+    end
+    assert_equal("hey\n", capture)
+  end
+
   def test_display
     pipe(proc do |w|
       "foo".display(w)