bug#65604: [PATCH] Display the exit code if the last command failed in Eshell

[Jim Porter]

On 8/29/2023 3:24 PM, Davide Masserut via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
> Tags: patch
>
> There are commands that fail without printing any messages, but set 
> specific error codes.
>
> This patch extends the default prompt function to show the exit code of 
> the previous failed command.

Thanks. I think this makes sense as an option, but I wonder if this is 
the right default place to put it. Instead, what about putting the exit 
status in the mode-line, like with compilation buffers? Eshell already 
uses the mode-line to show when a command is running, so I think it's an 
obvious enhancement to show the status of a command that just finished 
running. This does mean you don't see the *history* of failed commands, 
but it still provides useful feedback for users without requiring a 
change to the prompt (which is a bit more in-your-face).

In the future, I hope to make it easier for people to customize the 
Eshell prompt without writing (as much) Elisp, e.g. by defining it the 
same way we can define the mode-line. However, I haven't finished up 
that patch yet, so it's sitting on one of my pile of local branches...