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

[Max Nikulin]

On 04/06/2022 20:42, Ihor Radchenko wrote:
> It appears that using mailcap is giving us more trouble than benefits.
> I am not sure about the situation on Windows and Mac though.
>
> Should we change the default file handlers to Emacs globally (unless
> user customizes otherwise)? Should we continue efforts to work around
> mailcap issues? Maybe there is yet another alternative generic way to
> open files?

First of all, does someone has reproducible examples when 
`org-open-file' behaves against expectations in *default* configuration?

My current impression is that even despite serious problems with wiping 
of `mailcap-mime-data' in Emacs-27, "most" files are still opened in 
Emacs due to `auto-mode-alist'. Mailcap is used more rare than I expected.

I believe, there are enough issues with mailcap implementation in Emacs, 
but do we have some alternative? There is no support of queries to 
mimeapps.list files in Emacs (XDG). Like Chrome it is possible to call 
xdg-open for any type that can not be handled internally. Maybe it 
possible to leave it in Org as is or with the patch to call "file" 
utility (after some fixes).

At least Arch and Debian with Ubuntu have packages for SEMI 
(emacs-mime), but I am unsure what it is
http://git.chise.org/elisp/semi/
http://git.chise.org/gitweb/?p=elisp/semi.git;a=tree

P.S. Some observations.

MIME is mess. On my system I have in the /etc/mime.types file
application/x-sh                                sh
application/x-shellscript
text/x-sh                                       sh

Notice that for a file with no extension MIME type is different. The 
"file" utility reports another variant: "text/x-shellscript". To be on 
the safe side users should configure all variants...

Unsure if the latest version is the same
https://gitlab.freedesktop.org/xdg/shared-mime-info/-/raw/master/data/freedesktop.org.xml.in
  <mime-type type="application/x-shellscript">
    <comment>shell script</comment>
    <sub-class-of type="application/x-executable"/>
    <sub-class-of type="text/plain"/>
    <alias type="text/x-sh"/>
    <generic-icon name="text-x-script"/>
    <magic>
      <!-- ... -->
    </magic>
    <glob pattern="*.sh"/>
  </mime-type>

Emacs behavior for (mailcap-mime-info "text/plain") when no mailcap 
files are present in the system
- 26: view-mode
- 27: nil since initial value of `mailcap-mime-data' erased
- 28: fundamental-mode because when `mailcap-mime-data' is copied to 
`mailcap--computed-mime-data' order of fundamental-mode and view-mode is 
reverted.

By default user's ~/.mailcap has higher priority than initial 
`mailcap-mime-data' configuration in Emacs-28, but it was not so in 
Emacs-26.

Though it should not matter due to `auto-mode-alist'.

P.P.S. I had a hope that recent Fedora-36 release has Emacs-28 packaged, 
so it would be possible to test live image in qemu to quickly check 
behavior in full-fledged desktop environment, but version 27 is really 
packaged there.