[bug#47435] gnu: mail: Make the sendmail package actually output its binary

[Leo Famulari <leo@famulari.name>]

On Sat, Mar 27, 2021 at 06:34:03PM +0100, Rovanion Luckey wrote:
> This is an attempt at getting the sendmail package working. Currently
> installing the package does not make the `sendmail` executable appear in
> `$PATH`:
> 
> 
> > └$ guix environment --ad-hoc sendmail
> > └$ sendmail
> > bash: sendmail: command not found
> 
> This patch fixes that.
> 
> Though there are questions that still need to be resolved. While this patch
> does fix what it sets out to fix, the solutions aren't neccicerily correct.
> It configures a "helpfile" to be put in "$out/usr/share" and the same goes
> for its "statistics" file. I have no idea what these does and where they
> should go in reality. If someone happens to know, please do tell.

Thanks for working on this!

> +             (substitute* "cf/cf/Makefile"
> +               (("^MAILDIR=.*")
> +                (string-append "MAILDIR = "
> +                               (assoc-ref outputs "out")
> +                               "/etc/mail\n")))

In addition to Léo Le Bouter's comments, I suggest either omitting or
amending this part. A Maildir is where the user's emails will be kept,
but it cannot be stored in the build output, because that directory will
be immutable after the build is complete.

https://en.wikipedia.org/wiki/Maildir

What is the default?