bug#31841: ./pre-inst-env guix system no longer works without ~/.config/guix

[Mark H Weaver <mhw@netris.org>]

Hi,

ludo@gnu.org (Ludovic Courtès) writes:

> myglc2@gmail.com skribis:
>
>> Based on this thread I am now making guix like this ...
>>
>> guix environment guix --ad-hoc guile-sqlite3 --root=build-env -- make [MAKECMDGOALS]
>>
>> ... and using it like this ...
>>
>> source build-env/etc/profile
>> ./pre-inst-env guix COMMAND ARGS...
>
> Yeah we can improve the doc.  Currently, “Building from Git” mentions
> ‘guix environment guix’, but “Running Guix Before It Is Installed”
> doesn’t.  How about this:
>
> diff --git a/doc/contributing.texi b/doc/contributing.texi
> index 205c972ae..3f82f4bc2 100644
> --- a/doc/contributing.texi
> +++ b/doc/contributing.texi
> @@ -108,7 +108,9 @@ actually installing them.  So that you can distinguish between your
>  ``end-user'' hat and your ``motley'' costume.
>  
>  To that end, all the command-line tools can be used even if you have not
> -run @code{make install}.  To do that, prefix each command with
> +run @code{make install}.  To do that, you first need to have an environment
> +with all the dependencies available (@pxref{Building from Git}), and then
> +simply prefix each command with
>  @command{./pre-inst-env} (the @file{pre-inst-env} script lives in the
>  top build tree of Guix), as in@footnote{The @option{-E} flag to
>  @command{sudo} guarantees that @code{GUILE_LOAD_PATH} is correctly set
>
>
> Note that I purposely did not mention “--ad-hoc guile-sqlite3” because
> it has become unnecessary with commit
> c5a2e1ffcb029f50c4c18352cf378b61c41c625e.
>
> Likewise, I did not mention “source build-env/etc/profile” because
> “Building from Git” suggests using ‘guix environment guix’, which sets
> up the right environment variables.
>
> WDYT?

When running Guix exclusively from a git checkout and never running
'guix pull', something like "source build-env/etc/profile" must now be
run before running 'guix'.

You seem to be suggesting that "source build-env/etc/profile" could
simply be replaced by "guix environment guix".  One problem with this
idea is that it would introduce a circularity.  My 'guix' script cannot
very well begin by running 'guix environment guix'.

There are other problems as well:

(1) The build environment used to build the git checkout must be
    registered as a GC root, or else "guix gc" may render my git
    checkout of 'guix' non-functional, with no easy way to recover
    (at least not without running 'guix pull').

(2) When my git checkout is in a bad state, or is unbuilt, then during
    this time I'm unable to easily run "guix environment guix".  So, I
    always need a way to restore a known good development environment to
    rebuild my copy of guix, without using guix itself.  My method is to
    source the etc/profile from my saved development environment profile.

I should emphasize that when running Guix this way, if you wish to avoid
running 'guix pull', it's important to always keep at least one
known-good development environment for Guix saved as a GC root.  Toward
that end, when I run "guix environment guix" to update my development
environment profile, I make sure to preserve my previous profile as a GC
root until I'm confident that my new profile is working.

The suggested recipe involving "guix environment guix --root=build-env"
command is a nice improvement over my manual management of these GC
roots, but it has one shortcoming: it discards the older profile symlink
and GC root immediately, before it's known whether the new profile works.

This message should make it clear that when using Guix in this way, it's
easy to get stuck if you're not careful.  I suppose that I could always
get unstuck by running 'guix pull', but I prefer to avoid it.

     Regards,
       Mark