[bug#27438] [PATCH] Specify native search path for all ruby packages

[Ben Woodcroft <b.woodcroft@uq.edu.au>]

Hi,

[..]
>>>> In general, except for some special circumstances, we don't support
>>>> old versions of software. To fix the issue that you are
>>>> encountering properly with nokogiri probably requires new package
>>>> definitions using "package-with-ruby-2.3" or similar to be made, I
>>>> suppose. Ludo did some nice work making this easier (see
>>>> https://lists.gnu.org/archive/html/guix-patches/2017-04/msg00126.html),
>>>> but I worry in general about the resources required to support
>>>> older Ruby versions. WDYT?
>>> I'm not aware of any particular problems if you are working with the
>>> package definitions in Guile, as it should be possible to make them
>>> use the single ruby version that you want.
>>>
>>> With the guix environment command I posted:
>>>
>>>     guix environment --pure --ad-hoc ruby-nokogiri ruby@2.1 -- ruby
>>> -e "puts require 'nokogiri'"
>>>
>>> It would be ideal if there was some way of telling guix environment
>>> to rewrite the package definitions of all packages to use ruby@2.1
>>> in place of whatever ruby they might be using.
>> Is "package-mapping" sufficient?
> I don't think so. The ruby used is in the case of the ruby-build-system
> is an argument to the build system, so you need to traverse part of the
> dependency graph, altering the arguments of packages using the
> ruby-build-system.
>
> Or, perhaps do the transformation at a lower level abstraction than the
> package record...
For most compiled gems, I think it should be possible to write some 
procedure so that this would provide you with what you want:

guix environment --ad-hoc ruby@2.1 
--environment='(package-with-explicit-ruby ruby-2.1 ruby-nokogiri)'

For this specific case though, ruby-2.1 might not be the best example, 
since it is explicitly not supported any more.
>> If all Ruby dependencies build with this change, then the change
>> seems reasonable to me, details aside.
> Ok, does anyone know a good process for testing if lots of packages
> build? I think I've heard of Hydra building branches?
I believe we can go by the old standby "guix refresh -l ruby", so 659 
packages are rebuilt. Given this it would be appropriate for the staging 
branch, due to be merged after core-updates.

ben