Hello,

Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

>> It’s indeed the case that arguments can capture references to packages
>> that won’t be caught by ‘package-mapping’.  For instance, if you write:
>>
>>   (package
>>     …
>>     (arguments (list … #~(whatever #$coreutils))))
>>
>> … then ‘coreutils’ here cannot be replaced.
>>
>> To address this, the recommendation is to always add dependencies to
>> input fields and to use self-references within arguments.  The example
>> above should be written like this:
>>
>>   (package
>>     …
>>     (arguments
>>      (list … #~(whatever #$(this-package-input "coreutils")))))
>>
>> It’s just a recommendation and one can perfectly ignore it, and I
>> suppose that was the impetus for this patch.
>>
>> This is one of the things discussed while designing this change:
>>
>>   https://guix.gnu.org/en/blog/2021/the-big-change/
>>   (search for “self-referential records”)
>>
>>   https://issues.guix.gnu.org/49169
>>
>> My take was and still is that it’s an acceptable limitation.  Packagers
>> need to follow the guideline above if they want proper support for
>> rewriting, ‘guix graph’, and other tools.
>>
>> WDYT?
>
> But not all packages found in a bag come from inputs; they may be
> provided as an argument to the build system (cmake, meson, qt, etc. all
> allow for this).

Yes, but these packages (#:cmake for ‘cmake-build-system’, #:python for
‘python-build-system’, etc.) become inputs of the bag, and are taken
into account, as in this example:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix show tinyxml2
name: tinyxml2
version: 8.0.0
outputs:
+ out: everything
systems: x86_64-linux i686-linux
dependencies: 
location: gnu/packages/xml.scm:1295:2
homepage: http://www.grinninglizard.com/tinyxml2/
license: Zlib
synopsis: Small XML parser for C++  
description: TinyXML2 is a small and simple XML parsing library for the C++ programming
+ language.

$ ./pre-inst-env guix build tinyxml2
The following graft will be made:
   /gnu/store/qf8w8ch1mrxk6k34g2d6bisny5pq8gnv-tinyxml2-8.0.0.drv
applying 2 grafts for tinyxml2-8.0.0 ...
grafting '/gnu/store/ndzyiwhypsbgrbaz7rmz3649b6ghlfal-tinyxml2-8.0.0' -> '/gnu/store/2da5frl36gd51653bjjypqvwdk0bh25v-tinyxml2-8.0.0'...
successfully built /gnu/store/qf8w8ch1mrxk6k34g2d6bisny5pq8gnv-tinyxml2-8.0.0.drv
/gnu/store/2da5frl36gd51653bjjypqvwdk0bh25v-tinyxml2-8.0.0
$ ./pre-inst-env guix build tinyxml2 --with-input=cmake-minimal=cmake
The following derivation will be built:
  /gnu/store/hx0hx1nrmxzdhy9yw1d0md2q78y4spd4-tinyxml2-8.0.0.drv
8.4 MB will be downloaded:
  /gnu/store/qwy25ivr63087x9fdl9km0m44hn5bimg-cmake-3.25.1
  /gnu/store/3vh9b2i93na8wwdrj6n0q2qbgd2fzxik-tinyxml2-8.0.0-checkout

[...]

/gnu/store/cmn551x8iksy44cdqypyq2129lm8ym60-tinyxml2-8.0.0
--8<---------------cut here---------------end--------------->8---

(In this case I had to apply the patch below because ‘cmake-minimal’ was
mistakenly marked as hidden which, as implemented by
eee95b5a879b7096dffd533f24107cf8926b621e, meant that it could not be
replaced.)

I gave a similar example with ‘python-build-system’ here:

  https://issues.guix.gnu.org/65665#10

My understanding is that understanding is that this patch series is
about addressing cases as I explained above, where ‘arguments’ refer to
packages directly instead of using self references.  Do I get this
right, Ulf?

Thanks,
Ludo’.