[Blog/Cookbook?] On multiple Guix profiles and manifests

[Pierre Neidhardt]

Hi!

While the documentation refers to profiles and manifests, it does not tell much
of the use cases and the practical benefits.

For users coming from non-functional package managers, it's not really obvious
why we would need profiles.

Regarding manifest, I suppose some people might find them annoying to use
because updating/adding just 1 program means rebuilding the whole profile, which
after a Guix pull can be somewhat lengthy.

So what about writing a blog article / cookbook chapter to explain why
profiles and manifests are truly awesome indeed?  (Unless this has
already been done and I missed it?)

A quick 'n' dirty outline:

A manifest can be slow to install if it's too big.  But Guix supports profile,
which are perfect to break down manifests into multiple sets of semantically
connected packages.

Example profiles:

- Emacs.
- TeXlive (this one can be really useful when you need to install just one
  package for the next document you've received over email).
- Your favourite programming language libraries.
- The dependencies of a project you are working on
- Games :p

We can create a manifest per profile and install them this way:

  guix package --manifest=/path/to/guix-dev-manifest.scm  
--profile=$HOME/.guix-extra-profiles/dev/dev
  
Placing all your profiles in a single folder, with each profile getting its own
subfolder is somewhat cleaner, plus it's obvious to "loop over profiles" from
any programming language (e.g. a shell script) by
simply looping over the sub-directories of .guix-extra-profiles.

Note that it's also possible to loop over the output of `guix package
--list-profiles` although you'll probably have to filter out
`~/.config/guix/current`.


To "enable" all profiles on login, add this to your .bash_profile (or .profile
if you don't use bash):

#+begin_src sh
for i in ~/.guix-extra-profiles/*; do
        profile=$i/$(basename "$i")
        if [ -f "$profile"/etc/profile ]; then
                GUIX_PROFILE="$profile" ; . "$profile"/etc/profile
        fi
        unset profile
done
#+end_src

I like to keep the default ~/.guix-profile manifest-less for trash-away packages
that I would just use for a couple of days.  
This way it's easy to just run

  guix install FOO
  guix upgrade BAR
  
and I don't have to specify the profile.

Other benefits of manifests:

- No need to generate or maintain a manifest from an ad-hoc profile.
  
- "guix package -u" will always suggest to update some packages of those have
  propagated inputs.  Guix manifests avoid this problem.
  
- "guix package -u [packages...]" may report conflicts which are annoying to
  resolve manually.  Manifests avoid this problem altogether.

Other benefits of multiple profiles

- It's easy to toggle a specific profile on/off.
  
- When a profile is off, it's easy to enable it for an individual shell without
  "polluting" the rest of the user session:

  #+begin_src sh
  GUIX_PROFILE="$profile" ; . "$profile"/etc/profile 
  #+end_src


Happy to hear about your feedback!

Cheers!

-- 
Pierre Neidhardt
https://ambrevar.xyz/

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