Re: A plan for parameterized packages

["Ludovic Courtès" <ludo@gnu.org>]

Hi Stephen,

(+Cc: guix-devel@gnu.org.  You can post without being subscribed.)

Stephen Christie <spc@e.email> skribis:

> I have done a lot of work with the Conan package manager, a c++
> language package manager, that has grown in capability. It is not
> fully functional, but works on the hash of the key parameters of the
> package (name, version, etc.) to find the right reproducible
> binary. Two important parameters are "options" and "settings".
>
> Options are per-package, and generally affect none below it. You can
> specify defaults for the options in the package, and also call for
> specific options on dependencies in package "recipes". There are also
> ways to define incompatibilities and substitutes. On the command line,
> you can specify options with -o,--options, with no namespace needed
> for the package you are installing, and package:option to specify for
> other packages pulled in. I prefer this syntax to all the equal signs
> you proposed (though I defer if this is standard throughout
> Guix/Guile)
>
> Settings are more "system-wide", though being a language package
> manager, it does not have a "system". The same settings are applied to
> the whole tree during an install, and are usually things like
> compiler, architecture, and build type. These settings are chosen
> through a profile file, of which there is a default generated for a
> given computer. Settings can also be set at the command line during
> install with -s,--settings, but of course there is no namespacing.
>
> https://docs.conan.io/en/latest/mastering/conditional.html
>
> I think there is a lot of good stuff in Conan that Guix could learn
> from. It's a lot closer in architecture than any of the traditional
> system package managers.

Thanks for sharing Conan’s perspective on these issues!

The settings/options distinction looks like a useful one.  Like Pierre
suggested, it’d be nice to have options that apply to the whole graph in
addition to per-package options like I was focusing on.

Conan’s approach to conflicting options may not be applicable to Guix.
For instance, the manual above has this example:

  def configure(self):
    # …
    if self.settings.os == "Windows":
       self.options["openssl"].shared = True

  def requirements(self):
      # Or add a new requirement!
      if self.options.testing:
         self.requires("OpenSSL/2.1@memsharded/testing")
      else:
         self.requires("openssl/1.0.2u")

In Guix, instead of stating that OpenSSL 1.0.2u is required or that it
needs to include shared libraries, you’d actually depend on a variant of
OpenSSL that fulfills these constraints; by construction, you can be
sure you have the intended OpenSSL variant (generally speaking, a Guix
package dependency graph has zero degrees of liberty, unlike an
apt/Spack/Conan graph.)

As for the syntax… yeah, we could find a shorthand.  :-)  The verbosity
in the examples I gave partly stems from the fact that these are
per-package parameters, so you need to specify which package it applies
to.  With “global” parameters, we could have, say:

  guix install -P x11=false emacs

meaning that the ‘x11’ parameter will be set to #f in all the packages
that have such a parameter.

Thanks,
Ludo’.