Re: Org mode links: Open a PDF file at a given page and highlight a given string

[Maxim Nikulin <manikulin@gmail.com>]

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On 03/03/2021 05:36, Kyle Meyer wrote:
> Rodrigo Morales writes:
> 
> [...]
>> + create a Org link to specific pages of a PDF and highlight a given
>>    string.
>>
>> #+begin_src emacs-lisp :results silent
>> (setq org-file-apps
>>        '(("\\.pdf::\\([0-9]+\\)::\\([^:]+\\)\\'" . "zathura -P %1 -f %2 %s")))
>> #+end_src
>>
>> The following link must open the PDF at a given page and highlight the
>> given string. However, I'm getting the following error (see the
>> =#+begin_example= block below.)
>>
>> [[file:~/Downloads/grub.pdf::95::do]]

Correct link should be [[info:grub#true]] (a joke, at least a kind of).

Actually I never considered search string for highlighting of particular 
text, so thank you for the hint. Browsers could generate (mutually 
incompatible) link to particular rectangle. With xpopple (fork of old 
xpdf) it is possible to send command to select region.

However I think it is better to use logical links instead of page numbers:

    okular --find do ~/Downloads/grub.pdf'#true'
    xpdf ~/Downloads/grub.pdf +true

Unfortunately firefox replaces "#" to percent-encoded sequence in 
command line argument and could not find the file. It requires editing 
in address bar.

>> #+begin_example
>> Debugger entered--Lisp error: (wrong-type-argument stringp nil)
>>    replace-match(nil t t "zathura -P 95 -f %2 /home/username/Downloads/grub....")
> 
> I haven't looked at this closely or tried to trigger the error, but an
> in-flight patch is touching this area
> (<https://orgmode.org/list/87mtw8fupl.fsf@kyleam.com>).  I've yet to
> revisit it to address Maxim's helpful feedback, but I hope to soon and
> will look at this error then too.

Kyle, your patch works for such handlers. This case is another argument 
to replace all substitutions in a single pass. Global state (match data) 
is the source of the problem.

I am attaching informal single-line patch for quick plumbing. 
Alternative is to use save-match-data around string-match inside the loop.

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diff --git a/lisp/org.el b/lisp/org.el
index fd6226702..f45adb308 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -8757,8 +8757,8 @@ If the file does not exist, throw an error."
       (save-match-data
 	(let ((match-index 1)
 	      (number-of-groups (- (/ (length link-match-data) 2) 1)))
-	  (set-match-data link-match-data)
 	  (while (<= match-index number-of-groups)
+	    (set-match-data link-match-data)
 	    (let ((regex (concat "%" (number-to-string match-index)))
 		  (replace-with (match-string match-index dlink)))
 	      (while (string-match regex cmd)