bug#56013: 28.1; "gio open" and "xdg-open" fail silently under eshell

[Jeff Kowalski <jeff.kowalski@gmail.com>]

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While I cannot help to craft the solution (I'm limited by my knowledge of
internals here), I'm very happy to help test proposals.  It seemed there
was a hint of a solution developed in this thread.

On Fri, Jun 17, 2022 at 11:25 AM Jim Porter <jporterbugs@gmail.com> wrote:

> On 6/17/2022 10:17 AM, Jim Porter wrote:
> > On 6/17/2022 4:59 AM, Lars Ingebrigtsen wrote:
> >> Andreas Schwab <schwab@linux-m68k.org> writes:
> >>
> >>> See bug#44824.
> >>
> >> Ah, right.  The fix proposed there was:
> >>
> >>      org.el: Avoid xdg-open silent failure
> >>      * lisp/org.el (org-open-file): Use 'pipe :connection-type instead
> of
> >>      'pty to prevent killing of background process on handler exit.
> >>
> >> Perhaps Jim has some comments here; added to the CCs.
> >
> > Yeah, this is an issue with how `start-file-process' is being called in
> > Eshell (see `eshell-gather-process-output'). If I call `(setq
> > process-connection-type nil)' before running gio in Eshell, it works
> fine.
>
> Oh right... I remember looking at a related issue before. Note: I don't
> think this will directly fix the issue in this bug, but it might affect
> how we do fix this, so I'm mentioning it here.
>
> `eshell-needs-pipe-p' has a link to bug#1388, which discusses why that
> function exists in the first place. Basically, if `eshell-needs-pipe-p'
> didn't exist, then the following Eshell command wouldn't work right[1]:
>
>    ~ $ *echo "1+1" | bc
>
> However, the solution isn't quite right if you think about it: while
> it's true that bc's stdin should be a pipe, couldn't its stdout still be
> a pty? The all-or-nothing nature of "pipe vs pty" seems a bit
> over-restrictive. For example, this is (part of) why piping to `less' is
> so broken in Eshell. If you remove "less" from `eshell-visual-commands',
> you can see some of the issues. The following works ok, though you get
> the "dumb terminal" interface for less:
>
>    ~ $ less file.txt
>
> But this fails:
>
>    ~ $ cat file.txt | less
>    Missing filename ("less --help" for help)
>
> I believe that's because `less' sees that stdin is a pty in that case
> and so it expects a filename. However, adding `less' to
> `eshell-needs-pipe' fails though because then `less' thinks stdout is a
> pipe too, so you don't even get the dumb terminal UI; it just forwards
> stdin to stdout unchanged.
>
> Fixing this would get rid of the current uses for `eshell-needs-pipe-p',
> but then we'd probably want to keep it around in a slightly different
> form in order to handle gio/xdg-open properly. What we do about the
> issue described above would probably determine how the contents of
> `eshell-needs-pipe' should be specified.
>
> [1] The "*" in that command is to use the real /bin/echo, since bc
> expects a trailing newline and Eshell's built-in echo doesn't do that.
>

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