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Re: add-to-list on lexical vars (Re: Error on loading polyglossia.el)

From: Tassilo Horn
Subject: Re: add-to-list on lexical vars (Re: Error on loading polyglossia.el)
Date: Sat, 09 Jan 2021 10:41:59 +0100
User-agent: mu4e 1.5.7; emacs 28.0.50

Ikumi Keita <> writes:

Hi Ikumi,

>>> I did notice, BTW, that this function uses `add-to-list`, the doc
>>> string of which warns against using it in Lisp code.
>> Yes, you should definitely not use it on lexical local variables.
>> With AUCTeX 13, we switched to lexical-binding, and now that doesn't
>> work anymore.
> According to the output of "git grep add-to-list", there are still
> some usage of `add-to-list' on lexical scope variables, and I made the
> attached patch. Does this look reasonable?

Yes, looks good to me.

> What is strange to me is that those wrong usages of `add-to-list'
> don't cause error in a way the former polyglossia.el troubled Joost.
> Customizing `TeX-view-program-list' and `TeX-view-program-selection'
> in custom buffer proceeds smoothly 

I think the reason is that those usages are in back-ticked forms and
defcustom is a macro, and the expansion doesn't have those add-to-list
usages anymore.  And probably the code being run in the macro expansion
phase isn't byte-compiled because it's a one-shot business anyway.

> and `TeX-add-to-alist' runs without error for me, even without the
> patch.

Not for me.  Just eval in *scratch* which has lexical-binding at least
in my emacs master checkout:

--8<---------------cut here---------------start------------->8---
(let ((alist nil))
  (TeX-add-to-alist 'alist '((a 1)))
  alist) ;; <== C-j here

Debugger entered--Lisp error: (void-variable alist)
  TeX-add-to-alist(alist ((a 1)))
  (let ((alist nil)) (TeX-add-to-alist 'alist '((a 1))) alist)
  (progn (let ((alist nil)) (TeX-add-to-alist 'alist '((a 1))) alist))
  eval((progn (let ((alist nil)) (TeX-add-to-alist 'alist '((a 1))) alist)) t)
  funcall-interactively(eval-last-sexp nil)
  call-interactively(eval-last-sexp nil nil)
--8<---------------cut here---------------end--------------->8---

However, it works fine when I eval the form in this mail buffer (where
lexical-binding is nil).

While you are at it, could you please add some TeX-add-to-alist tests to
our suite.  Looking at your relevant diff hunk it is obvious that this
function isn't trivial and some tests are justified.


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