bug#72117: Command doesn't execute correctly in eshell

[Jim Porter]

On 7/14/2024 6:01 PM, Jim Porter wrote:
> On 7/14/2024 12:33 PM, the_wurfkreuz via Bug reports for GNU Emacs, the 
> Swiss army knife of text editors wrote:
>   But that's not the most interesting part. I can execute the
> > command with 'eshell/sudo'. But after the command execution emacs will
> > take the whole CPU processing time if i have 
> > '(global-display-line-numbers-mode 1)'
> > option enabled.
>
> I can't reproduce this particular issue, but I can reproduce *an* issue. 
> It seems to be due to "head -10" exiting early (as it should), which 
> results in a broken pipe. However, Eshell's broken pipe handling wasn't 
> properly cleaning up the process ("grep" in this example).

Eli, would this patch (re-attached here) be ok for Emacs 30? It's not a 
perfect solution (the fix currently on master is much better), but it's 
the least-risky change to this code that I could make, and it should 
improve matters somewhat for the release branch.

To summarize the problem so you have a bit more context for what this is 
changing: in Eshell, if you have a pipeline like "cat some-file | head 
-10", then the "head" process can exit early and raise an 
'eshell-pipe-broken' signal. The process filter for "cat" will catch 
this signal and try to send SIGPIPE to the actual "cat" process. 
However, for MS-Windows (which doesn't have SIGPIPE), and Tramp (where I 
couldn't get 'signal-process' to work due to another bug[1]), it just 
deletes the process. Unfortunately, that was failing to clean up the 
stderr "process" object, which caused Eshell to think the command wasn't 
complete. By changing to 'kill-process', this cleanup happens and things 
work more smoothly.

If you'd prefer to leave it as-is on Emacs 30, I don't mind either. This 
bug has been present since 29.1, and it took quite a while for anyone to 
notice it, so it probably doesn't come up terribly often.

[1] This is now fixed.

0001-Use-kill-process-as-a-fallback-when-a-pipe-gets-brok.patch
Description: Text document