Subject: bug#56773: 29.0.50; (readablep UNREADABLE) causes strange things

From: Lars Ingebrigtsen <[email-masked]>
Date: Tue, 26 Jul 2022 14:44:31 +0200

Eli Zaretskii <[email-masked]> writes:

> unwind_protect?

Where would the unwind_protect be?

The problem is here:

  if (!NILP (Vprint_unreadable_function)
      && FUNCTIONP (Vprint_unreadable_function))
    {
      specpdl_ref count = SPECPDL_INDEX ();
      /* Bind `print-unreadable-function' to nil to avoid accidental
	 infinite recursion in the function called.  */
      Lisp_Object func = Vprint_unreadable_function;
      specbind (Qprint_unreadable_function, Qnil);
      Lisp_Object result = CALLN (Ffuncall, func, obj,
				  escapeflag? Qt: Qnil);

We need to switch back to the original buffer before that Ffuncall, but
we don't know what the original function was -- it's just stored in a
local variable in prin1(-to-string).