bug#63916: 30.0.50; use-package: changes do not propagate to elpa-devel

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> But if I disable sandboxing, then it works.  The issue appears to be
> that the files under package/use-package are linked in using symlinks,
> but the directory (the emacs checkout) that is being linked to is not
> exposed via bwarp.  If I add that to the ro-binds, then I can build the
> package.  This diff might be enough to resolve the issue:
>
> diff --git a/elpa-admin.el b/elpa-admin.el
> index 24dd16d3cb..81467aa628 100644
> --- a/elpa-admin.el
> +++ b/elpa-admin.el
> @@ -1262,7 +1262,8 @@ The INFILE and DISPLAY arguments are fixed as nil."
>      "--tmpfs" "/tmp"))
>  
>  (defvar elpaa--sandbox-ro-binds
> -  '("/lib" "/lib64" "/bin" "/usr" "/etc/alternatives" "/etc/emacs" "/gnu"))
> +  `("/lib" "/lib64" "/bin" "/usr" "/etc/alternatives" "/etc/emacs" "/gnu"
> +    ,(file-truename (expand-file-name "emacs"))))
[...]
> CC: Stefan, does this look OK to you?

Building of :core packages outside of `elpa.gnu.org` is indeed tested on
very lightly.  In `elpa.gnu.org`, the `emacs` subdirectory is not
a symlink so we avoid that problem.

The above patch feels a bit hackish because it depends on the
directory that happens to be current when the file is loaded.

BTW, you should be able to make the current code work without changing
it, by adding

    (sandbox-extra-ro-dirs "/where/ever/your/emacs/source/dir/is")

to the `elpa-config` file.


        Stefan