bug#25965: 26.0.50; iter-lambda may evaluate certain forms twice

[Daniel Colascione <dancol@dancol.org>]

On Wed, Mar 08 2017, Stefan Monnier wrote:
>> The unwind-protect form is created in this function.
>>
>> #+BEGIN_SRC emacs-lisp
>>   (defun cps--make-dynamic-binding-wrapper (dynamic-var static-var)
>>     (cl-assert lexical-binding)
>>     (lambda (form)
>>       `(let ((,dynamic-var ,static-var))
>>          (unwind-protect ; Update the static shadow after evaluation is done
>>               ,form
>>            (setf ,static-var ,dynamic-var))
>>          ,form)))
>> #+END_SRC
>>
>> And it seems to me that the second occurrence of ,form is just an
>> error.
>
> Hmm... indeed that looks odd, and maybe just removing the second ,form
> is the right fix.  Daniel, do you happen to remember what the second
> ,form above is meant to do?

Embarrass me years later? :-) I think it's safe to remove it. Let's make
sure to add a test too.