Re: hg-histedit, how to pass shell involvement, to the lisp code?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 09 Oct 2024 21:36:19 +0200
> From:  Uwe Brauer via "Emacs development discussions." <emacs-devel@gnu.org>
> 
> In mercurial the command histedit, allows, well to rewrite history, (log
> messages etc).
> 
> The emacs pkg hg-histedit (pkg seems abandoned) now allows one to use
> this command entirely within emacs, the relevant code lines are
> 
> (defcustom hg-histedit-executable "hg"    
> 
> 
> And the crucial lines in the main function
> 
> 
> (let ((output-buffer (generate-new-buffer " *hg-histedit*"))
>           (commands (if changeset
>                         `(,hg-histedit-executable "histedit" "--rev" ,changeset)
>                       `(,hg-histedit-executable "histedit"))))
> 
> However when run it this way, the editing takes place in /tmp (which is the
> default for mercurial) and not in the directory of the repository in
> question.
> 
> >From the command line this can be changed by 
> 
>     1. Bash TMP=$(hg root) hg histedit (or  TMP="$(hg root)" hg histedit
> 
>     2. Tcsh set TMP=`hg root`; hg histedit $argv
> 
> Then histedit runs in the directory of said repository.
> 
> Now my question is: how can I modify the lisp code to have this behavior
> I just described?

You are asking how to inject an environment variable into the
environment of a program that Emacs will run?  The way to do it is to
bind process-environment around the call to call-process or similar,
and add TMP=whatever to the value of process-environment inside the
let form.  Example from comint.el:

  (let ((process-environment
	 (nconc
          (comint-term-environment)
	  (list (format "INSIDE_EMACS=%s,comint" emacs-version))
          (when comint-pager
            (if (stringp comint-pager)
                (list (format "PAGER=%s" comint-pager))
              (error "comint-pager should be a string: %s" comint-pager)))
	  process-environment))