bug#22027: 25.1.50; Return uncorrupted default string

[Tino Calancha <f92capac@gmail.com>]

On Sat, 3 Jun 2017, npostavs@users.sourceforge.net wrote:

> Tino Calancha <f92capac@gmail.com> writes:
>
>> +                    (setq success (copy-sequence first))
>> +                  (when (and (arrayp first)
>> +                             (not (string= first "")))
>> +                    (clear-string first)
>> +                    (clear-string second)))
>
> I think that is too complicated, how about this instead:
Yes, your is better.  Thank you.
We might add a test as well:

commit eb7fdeefadf08d7a781bee60df45fb045b582930
Author: Tino Calancha <tino.calancha@gmail.com>
Date:   Mon Jun 5 09:18:55 2017 +0900

     * test/lisp/subr-tests.el (subr-tests-bug22027): Add test.

diff --git a/test/lisp/subr-tests.el b/test/lisp/subr-tests.el
index c0bfd40f80..81f61220d3 100644
--- a/test/lisp/subr-tests.el
+++ b/test/lisp/subr-tests.el
@@ -28,6 +28,7 @@
  ;;; Code:

  (require 'ert)
+(eval-when-compile (require 'cl-lib))

  (ert-deftest let-when-compile ()
    ;; good case
@@ -316,5 +317,13 @@ subr-tests--this-file
    (should-not (method-files 'subr-tests--undefined-generic))
    (should-not (method-files 'subr-tests--generic-without-methods)))

+(ert-deftest subr-tests-bug22027 ()
+  "Test for http://debbugs.gnu.org/22027 ."
+  (cl-letf* ((default "foo")
+             ((symbol-function 'read-string)
+              (lambda (&rest args) (mapconcat #'string default ""))))
+    (should (string= default (read-passwd "pass: " 'confirm default)))))
+
+
  (provide 'subr-tests)
  ;;; subr-tests.el ends here