Re: [DISCUSSION, default settings] Using mailcap as default handler for opening file links

[Max Nikulin]

On 13/02/2024 18:27, Ihor Radchenko wrote:
> Max Nikulin writes:
>
> I am mostly going to address user confusion about mailcap

XDG configuration and so xdg-open behavior is often confusing to users 
as well, especially in the cases of KDE and no DE. In GNOME it is 
alleviated by a step with the application chooser if default application 
has not been set yet.

> (1) a number
> of people are using DMs that rely on FreeDesktop and xdg-open;

DM is display manager. Even DE (desktop environment) is not necessary, 
some toolkits and applications have their own implementations of XDG specs.

> (2) Emacs' mailcap does not implement the specification fully - only a
> subset of mailcap format is obeyed.

Agree. On the other hand, mailcap.el is aware that Emacs can handle some 
files internally. This feature should be preserved in some way. In 
addition, mailcap has to be used if neither DISPLAY nor WAYLAND_DISPLAY 
is set for current terminal.

> > xdg-mime is more close to the file(1) tool
>
> That might be a good alternative to file indeed; although file is
> probably more widely installed.

xdg-mime and xdg-open belong to the same package. In the case of no DE 
xdg-mime calls file(1) (if mimetype(1) is not installed).

> Yes, but mailcap is not documented in Emacs manual.

(info "emacs-mailcap") However it is not as useful as it should be.

> > Is it necessary to modify Org? Maybe an alternative is to add "xdg-open
> > %s" for */* to `mailcap-user-mime-data'.
>
> Do you mean changing the default value of `mailcap-mime-data'?

I am unsure what is a proper way to do it. I am not confident enough 
with the code that selects handlers for files.

> > > I believe that xdg-open issue has been fixed by you in
> > > https://git.savannah.gnu.org/cgit/emacs/org-mode.git/commit/?id=5db61eb0f
> > > org.el: Avoid xdg-open silent failure
> >
> > I am still not really comfortable due to the strategy to start external
> > processes diverged from methods used in browse-url.el.
>
> Is it related to the problem at hand?

- Eli had objections, but did not provide any details.
- Error handling code was dropped for the sake of Emacs-25.
- In the case of no DE, quit from emacs means terminating of started 
applications.
- I hope a bug I faced is exotic enough to never happen in real life.

Unfortunately another approach is a kind of trade-off, not an 
unambiguous advantage.

> AFAIK, xdg.el does not support xdg-open functionality. We cannot use it
> here.

`xdg-mime-apps' looks like a building block. However it is not enough 
and perhaps has enough bugs.

Ideally Emacs should provide API that uses either xdg.el or mailcap.el 
as backend depending on runtime and user configuration. Org is not the 
only package that needs it.

P.S.
Ihor, perhaps your clock is several minutes ahead.