Re: Patch for possible bug in TeX-find-macro-end-helper

[Ikumi Keita]

Hi Enrico,

>>>>> Enrico Flor <enrico@eflor.net> writes:

> Here are the positions where point lands after evaluating

>    (goto-char (TeX-find-macro-end-helper))

> with point at the beginning of the macro:

> \macro{first}
> {second}█

> \macro{first}█
>   {second}

> \macro{first} % comment
>   {second}█

> What happens is that whitespace in the second line is skipped only if
> the previous line ended with some comment.  Since "second" is parsed as
> the second argument of the macro in all three cases, I think
> TeX-find-macro-end-helper should return the position right after
> `{second}` in all three cases.  If this is correct, this patch should
> implement the behavior (it just modifies two regexps in that function).

Indeed. (The form to evaluate should actually be
  (goto-char (TeX-find-macro-end-helper (point)))
, but that doesn't matter much.)

> Please forgive the noise if this is in fact an intentional behavior.

I suppose that the reported difference is just accidental one without
any particular intention. So I think AUCTeX can accept your patch.

Here are some related thoughts:
(1) The former half of `TeX-find-macro-boundaries' has similar subtle
inconsistency. When I evaluate
(let (start-point)
        (save-excursion
          (catch 'abort
            (let ((parse-sexp-ignore-comments t))
              (when (condition-case nil (progn (up-list) t) (error nil))
                (while (progn
                         (condition-case nil (backward-sexp)
                           (error (throw 'abort nil)))
                         (forward-comment -1)
                         (and (memq (char-before) '(?\] ?\}))
                              (not (TeX-escaped-p (1- (point)))))))
                (skip-chars-backward "A-Za-z@*")
                (when (and (eq (char-before) (aref TeX-esc 0))
                           (not (TeX-escaped-p (1- (point)))))
                  (setq start-point (1- (point))))))))
        (goto-char start-point))
inside the "{second}" in the following examples, the third one leads to
error caused by `(goto-char nil)'.

\macro{first}
{second}

\macro{first}
  {second}

\macro{first} % comment
  {second}

\macro{first}% comment
  {second}

Thus I think `TeX-find-macro-boundaries' should be fixed as well.

(2) There are customize options slightly related to the current topic,
namely `texmathp-allow-detached-args' and
`reftex-allow-detached-macro-args'. They both default to nil, so maybe
we should introduce a new customize option to do similar fine-control
over the behavior of `TeX-find-macro-boundaries' and
`TeX-find-macro-end-helper'.

(3) There are two packages related to the current topic:
The document of amsmath tells, with respect to \\[<dimension>] inside
display math environment, that
,----
| Do not type a space between the \\ and the following [; only for display
| environments defined by amsmath the space is interpreted to mean that
| the bracketed material is part of the document content.
`----

The document of mathtools says that it allows users to write
\[
  \begin{gathered}
    [t] = 100 \\
    [v] = 200
  \end{gathered}
\]
where [t] isn't interpreted as an optional argument for gathered
environment. (This is package default behavior; "allowspaces" package
option can disable it.)

Thus if we are to be very strict, AUCTeX shouldn't consider separated
brackets as optional arguments for these cases. (I'm not sure whether
it's worth discriminating such strictly.)

Regards,
Ikumi Keita
#StandWithUkraine #StopWarInUkraine