Re: unwind-protect and inhibit-quit

[Felix Dietrich <felix.dietrich@sperrhaken.name>]

Felix Dietrich <felix.dietrich@sperrhaken.name> writes:

> Eli Zaretskii <eliz@gnu.org> writes:
>
>>> From: Thibaut Verron <thibaut.verron@gmail.com>
>>> Date: Fri, 16 Jul 2021 10:10:36 +0200
>>> Cc: help-gnu-emacs <help-gnu-emacs@gnu.org>
>>> 
>>> > You could use inhibit-quit, but that is generally a bad idea from the
>>> > UI point of view, when invoking potentially long-running functions:
>>> > you are preventing the user from interrupting that long function.  For
>>> > example, suppose the FTP command stalls for some reason.
>>> >
>>> 
>>> Now I'm curious too... Would something like this work?
>>> 
>>>  (let ((inhibit-quit t))
>>>    (setq process
>>>       (let ((inhibit-quit nil))
>>>          (ftp-setup-buffer host file))))
>>
>> It might, but I still suggest to bind inhibit-quit non-nil only for
>> short durations of time and as little as possible.  There be dragons.
>
> I just found the “with-local-quit” macro.  Itʼs comment says that the
> quit-flag “will not be handled until the next function call”.  Doesnʼt
> that imply that once the let form has a value to return, the assignment
> should go through?  Admittingly, this is a lot of guessing on my side,
> as I do not know Emacs internals.

Nevermind, the manual states (I added the ‘*’ as highlighting):
“Eventually, ‘inhibit-quit’ will become ‘nil’ again, such as when its
binding is unwound at the end of a ‘let’ form.  *At that time*, if
‘quit-flag’ is still non-‘nil’, *the requested quit happens
immediately.*”[1]  So there might be more happening at the end of a let.
I guess only the source will tell, and “there be dragons” is the
definitive warning to follow for now.

Footnotes:
[1]  (info "(elisp) Quitting")

-- 
Felix Dietrich