Re: Looking at function

[Dmitry Gutov <dgutov@yandex.ru>]

On 11.07.2022 22:14, Juri Linkov wrote:
>>> 1. Replace ‘looking-at’ with a call to the search function,
>>>      but keep it at point by prepending ‘\\=’ to the regexp.
>>>      Can it break a complex regexp?
>>
>> I suppose it can. Even a simple one (that has \\| inside without
>> a grouping).
> 
> This is what the fix for xref successfully uses in bug#53758
> with changes in perform-replace from bug#14013.  (However,
> none of these variants is suitable for replacing another call
> of looking-at in isearch-search-and-update.)

Right. Because xref basically uses literal matching, no alternations.

But it will break more complex cases.

>> Do we have a clear understanding of the idea behind this looking-at call?
>>
>> The comment says:
>>
>> 	  ;; Otherwise, if matching a regular expression, do the next
>> 	  ;; match now, since the replacement for this match may
>> 	  ;; affect whether the next match is adjacent to this one.
>> 	  ;; If that match is empty, don't use it.
>>
>> What happens if there are multiple adjacent matches in a row, not just 2?
>> I suppose the replacement could be performed for the first one, then the
>> next one is "popped" becoming the current and looking-at is called again
>> near its end?
>>
>> If so, perhaps a good alternative is to stop caring about whether those
>> matches are adjacent and always store the latest two matches, whether they
>> are next to each other or not.
> 
> The sole purpose of this "do the next match now" hack
> is to handle a special use case that is tested
> in test/lisp/replace-tests.el:
> 
>      ;; Test case from commit 5632eb272c7
>      ("a a a " "C-M-% \\ba SPC RET c RET !" "ccc") ; not "ca c"
> 
>      ;; Test case from commit 5632eb272c7
>      ("a a a " "\\ba " "c" nil t nil nil nil nil nil nil nil "ccc") ; not "ca c"

All right. So it seems the idea of keeping references to the two latest 
can work.

No idea how big the changes will have to be, though.