bug#46291: [PATCH] environment: Allow starting from existing profile

[宋文武]

Lars-Dominik Braun <lars@6xq.net> writes:

> Hi everyone,
>
> the attched patch allows starting a `guix environment` from an existing
> profile. Our use-case is this: We have profiles, created by
>
>       guix package -p /path -i &
>
> because we need to parse desktop files in /path/share/applications. Also
> this does the heavy-lifting (substitutes/building/grafting) upfront once
> and not when starting an environment. Then we start an application from
> this profile using
>
>       guix environment -C [&] -p /path -- jupyterlab [&]
>
> This is much faster (10x) for large profiles (i.e. JupyterLab) than
>
>       guix environment -C [&] -m manifest.scm -- jupyterlab [&]
>
> and makes sure the environment is exactly the same as
>
>       source /path/etc/profile
>
> I think there have been many discussions about how `guix environment`
> should work and this is certainly not the silver bullet, but it.s a huge
> improvement for us with very limited code changes required.

Look excellent to me, pushed, thank you!