Make mutiple packages from outputs (Was: A plan for parameterized packages)

[宋文武]

zimoun <zimon.toutoune@gmail.com> writes:

> Dear,
>
> On Sun, 15 Nov 2020 at 21:46, Danny Milosavljevic <dannym@scratchpost.org> 
> wrote:
>
>> * Enable/disable building the documentation.  I really don't need a 40 MiB
>> manual stored onto a 16 MiB firmware flash chip.  If that's better done as an
>> extra output, fair enough.
>
> Related (I hope) is: build packages with several outputs.  For instance,
> ’git’ has several 'outputs' ("send-email", "svn", etc.), so the list of
> "inputs" provides e.g., "subversion" even if I am only interested by
> e.g., "git:send-email".  This matters about closure.
>
> And it is maybe an occasion to revisit the museum, i.e., the TODO file:
>
> ** extend ‘propagated-build-inputs’ with support for multiple outputs
>
> #+BEGIN_SRC scheme
>   (outputs '("out" "include"))
>   (propagated-build-inputs
>     `(((("i1" ,p1 "o1")
>         ("i2" ,p2))
>        => "include")
>       ("i3" ,p3)))
> #+END_SRC
>
> For one reference:
>
>   <https://lists.gnu.org/archive/html/guix-devel/2020-06/msg00284.html>
>
>
> All the best,
> simon

I'd like to suggest another plan: Make every ‘output’ become a <package>
object, so ‘propagated-build-inputs’ doesn’t need to change.  Then we’ll
have something like debian’s source/binary packages [1] and archlinux’s
base/split packages [2].

Example:
--8<---------------cut here---------------start------------->8---
(define-public %gtk+
  (source-package
    (name "gtk+")
    (version "3.24.20")
    (source ...)
    (inputs ...)
    (native-inputs ...)
    (outputs
      `(("out" .
         (binary-package
           (name "gtk+")  ; version inherit from source
           (propagated ...)  ; per output propagated-inputs here
           (native-search-paths ...)
           (synopsis ...) ; can override package metadata
           (description ...)))
        ("gtk-update-icon-cache" .
         (binary-package
           (name "gtk-update-icon-cache")
           ...))))
    (arguments ...)
    (home-page ...)
    (synopsis ...)
    (descirption ...)
    (license ...)))

(define-public gtk+
  (source-package->binary-package %gtk+ "out"))

(define-public gtk-update-icon-cache
  (source-package->binary-package %gtk+ "gtk-update-icon-cache"))
--8<---------------cut here---------------end--------------->8---

[1] https://sources.debian.org/src/gtk+3.0/3.24.23-2/debian/control/
[2] 
https://github.com/archlinux/svntogit-packages/blob/packages/gtk3/trunk/PKGBUILD


We'll have to build some compatibility layer with existing ‘package’ and
adjust UI though.  I think this is possible and will bring various
benefits!