Hello,
Nicolas Goaziou <m...@nicolasgoaziou.fr> skribis:
> Ludovic Courtès <l...@gnu.org> writes:
[...]
>> • Packages such as ‘tzdata’ use labels to refer to non-package
>> inputs. These cannot be converted to the automatic labeling
>> style, or not without extra changes.
>
> Would it be possible to write something like
>
> (inputs (let ((tzcode (origin ...)))
> (list ... tzcode ...)))
>
> ?
Yes, but the problem is that the automatically-assigned label for
<origin> records is “_” (a placeholder), because origins have no name,
unlike packages.
Thus, this phase:
(replace 'unpack
(lambda* (#:key source inputs #:allow-other-keys)
(invoke "tar" "xvf" source)
(invoke "tar" "xvf" (assoc-ref inputs "tzcode"))))
… needs to be written differently, because there’s no “tzcode” label.
One option on ‘core-updates’ is to use gexps:
#~(modify-phases %standard-phases
;; …
(replace 'unpack
(lambda* (#:key source inputs #:allow-other-keys)
(invoke "tar" "xvf" source)
(invoke "tar" "xvf" #$tzcode))))
However, this style breaks common uses of ‘inherit’ and uses of the
inputs field: ‘tzcode’ here need not even be listed in ‘inputs’, and
consequently, you cannot easily inherit from ‘tzdata’ and give it a
different ‘tzcode’.
We need to find and encourage appropriate idioms for corner cases like
this. One option is the status quo: keep using labels in those rare
cases.
A crazier option would be to interpret input lists, when possible, as
both input lists and formal parameter lists for ‘arguments’. Assume a
package with:
(inputs (list foo bar baz))
The ‘arguments’ field, which is currently a thunk, would magically be
turned into:
(lambda (foo bar baz)
…)
That way, arguments could refer to #$foo etc., and that’d just do the
right thing when inputs are overridden.
This would be reaching a level of magic that may not be wise, and it may
be hard to implement.
> Could the new syntax accept both variables and specifications, e.g.,
>
> (list "glib:bin" foo "bar@2.3")
>
> ?
No! I mean, yes it could, but no, I don’t think that’s a good idea.
:-)
In terms of API, I prefer clarity; in this case, I think inputs should
be a list of packages or other “lowerable” objects, rather than a list
of “anything” that could be magically interpreted at run time.
More importantly, I think package specs are a UI feature, and that
packages should be separate from UI concerns. Specs are implemented in
(gnu packages), not in (guix …) for a reason: it’s a feature that makes
sense in the distro, not in the core Guix machinery where there’s no
“package set” to traverse.
I hope that makes sense!
Ludo’.
