bug#68593: 29.1; comment-dwim: Args out of range: "", 0, 1

bug#68593: 29.1; comment-dwim: Args out of range: "", 0, 1

[Frank Ruben]

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In GNU Emacs 29.1 (build 2, x86_64-w64-mingw32) of 2023-08-02 built on
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When in c-ts-mode.el and when having '(setq comment-end " ")' and when I
then
then run e.g. 'comment-dwim' or simpler '(comment-normalize-vars)', I'm
getting
'comment-dwim: Args out of range: "", 0, 1'.

The error comes from the two 'substring' calls in this s-sexp - where the
code
already contains my "fix" - both calls to 'substring' have been guarded by
'(if (string-equal ce "") "" ...)'.

There are surely smarter ways to fix that - if one knows what is supposed to
happen here :). But maybe that fix gives you a hint to the appropriate
solution.

(let ((ce (if (string= "" comment-end) "\n"
 (comment-string-strip comment-end t t))))
        (setq-local comment-end-skip
                    ;; We use [ \t] rather than \s- because we don't want to
                    ;; remove ^L in C mode when uncommenting.
                    (concat "[ \t]*\\(\\s>" (if comment-quote-nested "" "+")
                            "\\|" (regexp-quote (if (string-equal ce "") ""
(substring ce 0 1)))
                            (if (and comment-quote-nested (<= (length ce)
1)) "" "+")
                            (regexp-quote (if (string-equal ce "") ""
(substring ce 1)))
                            "\\)")))

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bug#68593: 29.1; comment-dwim: Args out of range: "", 0, 1

[Eli Zaretskii]

> From: Frank Ruben <frankruben27@gmail.com>
> Date: Fri, 19 Jan 2024 22:16:04 +0100
> 
> When in c-ts-mode.el and when having '(setq comment-end " ")' and when I then
> then run e.g. 'comment-dwim' or simpler '(comment-normalize-vars)', I'm getting
> 'comment-dwim: Args out of range: "", 0, 1'.
> 
> The error comes from the two 'substring' calls in this s-sexp - where the code
> already contains my "fix" - both calls to 'substring' have been guarded by
> '(if (string-equal ce "") "" ...)'.

Can you tell why do you set comment-end to such a value in c-ts-mode?
What is the purpose of such a strange setting?