bug#65665: package-mapping with #:deep? #t doesn't get all the implicit inputs

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi,

Ludovic Courtès <ludo@gnu.org> writes:

> Ulf Herrman <striness@tilde.club> skribis:
>
>> -(define (build-system-with-package-mapping bs rewrite)
>> +(define (build-system-with-package-mapping bs rewrite-input rewrite-argument)
>>    "Return a variant of BS, a build system, that rewrites a bag's inputs by
>>  passing them through REWRITE, a procedure that takes an input tuplet and
>>  returns a \"rewritten\" input tuplet."
>> @@ -1442,9 +1442,10 @@ (define (build-system-with-package-mapping bs rewrite)
>>      (let ((lowered (apply lower args)))
>>        (bag
>>          (inherit lowered)
>> -        (build-inputs (map rewrite (bag-build-inputs lowered)))
>> -        (host-inputs (map rewrite (bag-host-inputs lowered)))
>> -        (target-inputs (map rewrite (bag-target-inputs lowered))))))
>> +        (build-inputs (map rewrite-input (bag-build-inputs lowered)))
>> +        (host-inputs (map rewrite-input (bag-host-inputs lowered)))
>> +        (target-inputs (map rewrite-input (bag-target-inputs lowered)))
>> +        (arguments (map rewrite-argument (bag-arguments lowered))))))
>
> Aah, now I understand.  :-)
>
> 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).

-- 
Thanks,
Maxim