Re: Opening of links

[Max Nikulin]

On 23/09/2022 21:49, Guillaume MULLER wrote:
> - My OS settings are configured so that PDFs are opened in Evince. I 
> configured this with "xfce4-settings-manager > Default Applications" 
> (which runs "xfce4-mime-settings" under the hood) and it can be verified 
> with "xdg-open test.pdf" or by opening Thunar and clicking on "test.pdf".

I would name it desktop environment configuration since OS may have more 
settings and it is your issue.

These settings likely alters ~/.config/mimeapps.list
https://specifications.freedesktop.org/mime-apps-spec/mime-apps-spec-1.0.html
"Association between MIME types and applications"

Unfortunately Emacs does not support this part of XDG specs, so there 
are no ready to use functions to work with .desktop files and MIME 
associations. You may add entries calling xdg-open for file types you 
wish to the `org-file-apps' custom variable.

>    So, where in the world does org-mode/Emacs finds that it should use 
> Calibre instead of Evince?

You may have mailcap configuration where Calibre has higher priority 
than Evince, check /etc/mailcap
RFC 1524. A User Agent Configuration Mechanism For Multimedia Mail 
Format Information
https://www.rfc-editor.org/rfc/rfc1524.html

Emacs has limited support of mailcap and it is used by Org mode. 
Besides system configuration, Emacs has a set of predefined association. 
Unfortunately the latter is broken in Emacs-27, see
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=40247
#40247 - 27.0.90; mailcap-mime-data erased when parsing mime parts - GNU 
bug report logs

> - Now, I would like to circumvent this global OS behavior, so that Emacs 
> itself would be used specifically to open PDF links in files I open in 
> Emacs. When I was using Vanilla Emacs, I was advised to use pdf-tools, 
> and given a config that was working. I translated that into my DoomEmacs 
> config.org as follows:
>    (use-package! pdf-tools
>      :magic ("%PDF" . pdf-view-mode)
>      :config
>        (pdf-tools-install :no-query)
>      )
>    But apparently it does not override org's (default) behavior of 
> opening PDF file with external tools.

The code of `org-open-file' is tricky. You may instrument this function 
for debugging and step through it to realize what actually happens. 
Maybe pdf-tools vs. doc-view mode choice is controlled by `auto-mode-alist'.

Concerning external viewer configuration, you may adapt for Evince the 
following approach:
Max Nikulin. Re: Org mode links: Open a PDF file at a given page and 
highlight a given string. Sat, 3 Sep 2022 20:00:47 +0700. 
https://list.orgmode.org/tevj61$17d8$1@ciao.gmane.io