bug#56025: [WIP PATCH] 29.0.50; em-extpipe-test-2 times out on EMBA and Cygwin

[Jim Porter]

On 7/18/2022 1:09 AM, Michael Albinus wrote:
> I haven't tested, but it looks like it won't work with remote processes
> foo and bar. Something like
>
> --8<---------------cut here---------------start------------->8---
> ~ $ cd /ssh:remotehost:
> /ssh:remotehost:~ $ *ls | *grep a
> --8<---------------cut here---------------end--------------->8---

Hmm, yeah. We'll need to do something with the Tramp case. I think the 
minimal fix would be to update `tramp-sh-handle-make-process' so that it 
doesn't signal an error when :connection-type is a cons cell. That's 
pretty easy.

However, it seems that Tramp doesn't fully support :connection-type yet 
(testing on both Emacs 28.1 and 29). I used the following Python script, 
and tried a few varieties of `make-process' calls over Tramp. I'd expect 
that when I set :connection-type to `pipe', it would print False for all 
the streams, but it seems that the script always sees stdin and stdout 
as TTYs no matter what options I use.

------------------------------
#!/usr/bin/env python3

import sys
print('stdin: {}\nstdout: {}\nstderr: {}\n'.format(
    sys.stdin.isatty(),
    sys.stdout.isatty(),
    sys.stderr.isatty()
))
------------------------------

On the other hand, if I set :stderr to be a buffer, then the script 
*does* see stderr as a pipe, but that makes sense looking at the code: 
when using :stderr, Tramp redirects the process's stderr to a file (and 
then cats it back out).

Maybe there's a relatively easy way to get Tramp to respect 
:connection-type, but I tried a couple of things and they didn't work 
quite right. Still, that could be a followup for later. So long as it 
doesn't error out immediately when it's a cons cell, I think it would be ok.