bug#44824: 27.1; Org export as pdf and open file does not open it

[Maxim Nikulin]

On 30/01/2021 15:42, Eli Zaretskii wrote:
> > This works:
> > M-! xdg-open /tmp/test.pdf RET
> >
> > This doesn't work:
> > M-& xdg-open /tmp/test.pdf RET
> >
> > This doesn't work:
> > M-x shell RET xdg-open /tmp/test.pdf RET

Geraldo, "M-x shell" case is rather strange. Could you, please, confirm 
ones more that okular window with the file content does not appear if 
you call xdg-open from an *interactive* emacs shell buffer? The link to 
an emacs-orgmode list message, that I have posted earlier, explains why 
async-shell-command *may* fail while shell-command should work reliably. 
I am really surprised by failure when command is executed in a [e]shell 
buffer.

> How about asking the xdg-open developers to help us figure out the
> reason?  Or, failing that, debug xdg-open in the problematic
> situations to find out what fails there and why?  E.g., could it be
> that it fails because stdin/stdout is a PTY? what happens if you bind
> process-connection-type to nil when starting the async subprocess?

I do not think, it is xdg-open problem. It just calls kde-open5 that 
spawns actual handler and immediately exits.