challenge: Store item contents are returned in canonical order.

This allows the 'delete-duplicates' call in 'differing-files' to have
the intended effect.

Before that, a "guix challenge" invocation with three builds of a store
item, two of which are identical, would lead 'differing-files' to not
print anything, as in this example:

  $ ./pre-inst-env guix challenge python-numpy
  /gnu/store/…-python-numpy-1.17.3 contents differ:
    local hash: 07var0wn8fywxchldz5pjqpnlavrlbc8s81aqwsqyi0i7qlh6ka7
    https://ci.guix.gnu.org/nar/lzip/…-python-numpy-1.17.3: 07var0wn8fywxchldz5pjqpnlavrlbc8s81aqwsqyi0i7qlh6ka7
    https://bordeaux.guix.gnu.org/nar/lzip/…-python-numpy-1.17.3: 0cbl3q19bshb6ddz8xkcrjzkcmillsqii4z852ybzixyp7rg40qa

  1 store items were analyzed:
    - 0 (0.0%) were identical
    - 1 (100.0%) differed
    - 0 (0.0%) were inconclusive

With this change, 'differing-files' prints additional info as intended:

    differing file:
      /lib/python3.8/site-packages/numpy/distutils/fcompiler/__pycache__/vast.cpython-38.pyc

* guix/scripts/challenge.scm (archive-contents): Add tail call to
'reverse'.
(store-item-contents): Rewrite to use 'scandir' and recursive calls
instead of 'file-system-fold'.

0 files changed, 0 insertions, 0 deletions