Ludo,
The self.options["openssl"].shared does set the option for openssl, but this is
not different than providing `-o openssl:shared` on the command line; it uses
this to determine which package was actually requested. Conan packages are also
non-configurable in the end, stored as the hash of it's name and parameters.
This is probably done while calculating the tree before installing/building
everything, but once that tree is calculated, it is fixed.
Besides parameters determining the hash of the package,
OpenSSL/2.1@memsharded/testing and openssl/1.0.2u are most certainly separate
packages. Conan has this name/version@username/channel structure to help find
alternatives (semver is supported), but otherwise those are completely
different.
On November 17, 2020 10:31:12 AM EST, "Ludovic Courtès" wrote:
>Hi Stephen,
>
>(+Cc: guix-devel@gnu.org. You can post without being subscribed.)
>
>Stephen Christie 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’.
--
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