bug#44370: Cuirass fails building (some) packages from a custom-packages input

[Mathieu Othacehe <othacehe@gnu.org>]

Hey Ludo,

> Now, in Guix proper, the ‘license’ field should always be either a
> <license> or a list of <license> records.  The original code would
> “enforce” that (by failing hard if a package doesn’t follow the rule
> :-)), which I think is good.

You are right, missed that.

> Now, why is David’s use case influenced by the way (gnu ci) handles
> licenses?

David has some custom packages with the license set to "#f", causing the
following backtrace:

--8<---------------cut here---------------start------------->8---
guix/inferior.scm:247:2: ERROR:
  1. &inferior-exception:
      arguments: (quit 1)
      inferior: #<<inferior> pid: pipe socket: #<input-output: string
      7f1b3d1dabd0> close: #<procedure close-pipe (p)> version: (0 1 1) 
packages: #<promise #<procedure 7f1b3d1de940 at guix/inferior.scm:162:32 ()>>
table: #<promise #<procedure 7f1b46b3a780 at guix/inferior.scm:163:32 ()>>>
      stack: ((#f ("ice-9/boot-9.scm" 1763 13)) (raise-exception
      ("ice-9/boot-9.scm" 1666 16)) (raise-exception ("ice-9/boot-9.scm" 1668 
16)) (map1 ("srfi/srfi-1.scm" 585 17)) (map1 ("srfi/srfi-1.scm" 585 29)) (map1
("srfi/srfi-1.scm" 585 29)) (map1 ("srfi/srfi-1.scm" 585 29)) (map1
("srfi/srfi-1.scm" 585 29)) (map1 ("srfi/srfi-1.scm" 585 29)) (map1
("srfi/srfi-1.scm" 585 29)) (map1 ("srfi/srfi-1.scm" 585 29)) (map1
("srfi/srfi-1.scm" 585 29)) (#f ("gnu/ci.scm" 552 38)) (map1
("srfi/srfi-1.scm" 585 17)) (append-map ("srfi/srfi-1.scm" 672 15)) 
(hydra-jobs ("gnu/ci.scm" 516 4)) (#f ("ice-9/eval.scm" 158 9)) (#f
("ice-9/eval.scm" 158 9)) (with-exception-handler ("ice-9/boot-9.scm" 
1735 10)) (call-with-prompt ("ice-9/boot-9.scm" 717 2)) (dynamic-wind
("ice-9/boot-9.scm" 141 2)) (#f (#f #f #f)) (#f ("guix/repl.scm" 92 21)) 
(with-exception-handler ("ice-9/boot-9.scm" 1735 10)) (with-exception-handler
("ice-9/boot-9.scm" 1730 15)) (#f ("guix/repl.scm" 119 7)))
--8<---------------cut here---------------end--------------->8---

As the alist fields such as "description", "long-description",
"license", "home-page", "maintainers" are ignored by Cuirass anyway,
what would you think of removing them?

This should allow custom packages to be built by Cuirass even if they
are not fully defined.

Thanks,

Mathieu