Re: [BUG] in org-property-drawer-re?

[Thorsten Jolitz <tjolitz@gmail.com>]

Nicolas Goaziou <n.goaziou@gmail.com> writes:

Hello,

> Carsten Dominik <carsten.dominik@gmail.com> writes:
>
>> This is just a cheep way to match any character at all, because \000 should
>> not be part of any string (in C it indicates the end of a string).
>> In principle you could put any character you are sure will not turn up,
>> but \000 seems to be the safest choice.  It is
>> faster (I think) than "\\(.\\|\n\\)*" because the first will
>> just run fast and streight with a table lookup while the
>> latter need to always alternate between two alternatives.
>> I have not timed it, though.
>
> On that topic, I would add that "^\000" must be used with care, as it
> can lead to a stack overflow in regexp matcher error quite easily. In
> particular, it may be safe to use it to match a property drawer, which
> will not be very large, but I think it's wrong to use it to match
> regular blocks or drawers, which can have arbitrary long size.
>
> For example a regexp like "[^\000]\\." will fail when matching around
> 500 lines (72 characters long). Of course, constructs like
> "\\(.\\|\n\\)*\\." will also fail, but my point is that it is tempting
> to use "^\000" even though a regexp may not be the correct answer to the
> problem.

Conceptually it looks perfect(ly simple) to me, and I'm happy that I
discovered the pattern now by accident (better late than never), but
stack overflow is of course an important point.

Reminds me of my little [[https://github.com/tj64/org-hlc][org-hlc.el]]
library (hidden lines cookies)

,-------------------------------------------------------------------------------
| org-hlc.el implements hidden-lines-cookies for Org-mode
|
| hidden-lines-cookies (hlc) are small cookies at the end of each folded (and
| visible) headline in an Org-mode buffer that show the number of hidden lines
| before the next visible headline.
|
| hidden-lines-cookies can be handled with three user commands:
| org-hlc-show-hidden-lines-cookies, org-hlc-hide-hidden-lines-cookies, and the
| convenience command org-hlc-toggle-hidden-lines-cookies that toggles between
| the two other commands conditional on the last one executed.
|
| The appearance of the cookies can be customized by changing the values of four
| customizable variables: org-hlc-hidden-lines-cookie-left-delimiter (with
| default value "["), org-hlc-hidden-lines-cookie-right-delimiter (with default
| value "]"), org-hlc-hidden-lines-cookie-left-signal-char (with default value
| "#") and org-hlc-hidden-lines-cookie-right-signal-char (with default value
| "").
|
| Thus an exemplary folded headline with 165 hidden lines before the next
| visible headline might look like this when hidden-lines-cookies are shown:
|
| ,----------------- | *** Headline [#165] `-----------------
|
`-------------------------------------------------------------------------------

that was conceptually all 'wrong':

 - the cookies are written in the original buffer (but that could easily be
   changed to a temporary indirect buffer)
 - cookies are only shown/updated with explicit user commands

but it works even in 7000 lines .el or .org files. 

The other attempt to 'do it right' based on a library by Francois
Pinard, [[https://github.com/tj64/org-weights][org-weights.el]], uses
overlays and dynamic updates of the tree-weights via change hooks - much
better in theory - but somehow overwhelms Emacs capacities in big files
so that user experience is affected.

--
cheers,
Thorsten