bug#57129: 29.0.50; Improve behavior of conditionals in Eshell

[Eli Zaretskii]

> Cc: larsi@gnus.org, 57129@debbugs.gnu.org
> From: Jim Porter <jporterbugs@gmail.com>
> Date: Mon, 15 Aug 2022 09:14:04 -0700
> 
> > All the 4 commands do what you say they should do.
> 
> Hm, and I can't reproduce this on the prebuilt Emacs 29 snapshot from 
> July 18, which is from just before I merged the changes to 
> 'make-process', so it's definitely possible that this is due to those 
> commits.
> 
> Does reverting 4e59830bc0ab17cdbd85748b133c97837bed99e3 and 
> d7b89ea4077d4fe677ba0577245328819ee79cdc fix the issue? I checked 
> locally, and they should revert cleanly at least.
> 
> It might also be interesting to revert just the changes from d7b89ea in 
> lisp/eshell/esh-proc.el. I don't think any of the changes I made to the 
> C sources should impact this, since a) I was careful to keep the logic 
> as close to before as I could, and b) it just changes the logic for 
> creating a PTY, which doesn't work on MS Windows anyway.

None of these reverts fixes the issue.  I tried both the tests in
eshell-tests.el and the problematic command:

   *cat $<echo $eshell-in-pipeline-p | echo> | *cat

> I did notice one weird issue though, and maybe this has something to do 
> with the problem: on MS Windows, if I run any command with a 
> $<subcommand>, the second and subsequent times, it warns me about 
> changing the temp file, e.g.:
> 
>    3Zz80A has changed since visited or saved.  Save anyway? (yes or no)
> 
> This probably shouldn't do that, and it could definitely cause issues in 
> the tests, which can't prompt the user for things like that.

I guess this means you somehow reuse the same temporary file on
MS-Windows?  Maybe change the test a bit so that the file name
definitely differs?