pack: Prevent duplicate files in tar archives.

Tar translate duplicate files in the archive into hard links.  These can cause
problems, as not every tool support them; for example dpkg doesn't.

* gnu/system/file-systems.scm (reduce-directories): New procedure.
(file-prefix?): Lift the restriction on file prefix.  The procedure can be
useful for comparing relative file names.  Adjust doc.
(file-name-depth): New procedure, extracted from ...
(btrfs-store-subvolume-file-name): ... here.
* guix/scripts/pack.scm (self-contained-tarball/builder): Use
reduce-directories.
* tests/file-systems.scm ("reduce-directories"): New test.

1 files changed, 6 insertions, 1 deletions

diff --git a/tests/file-systems.scm b/tests/file-systems.scm
index 7f7c373884f..80acb6d5b91 100644
--- a/tests/file-systems.scm
+++ b/tests/file-systems.scm
@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015, 2017 Ludovic Courtès <ludo@gnu.org>
-;;; Copyright © 2020 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;; Copyright © 2020, 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -50,6 +50,11 @@
                    (device "/foo")
                    (flags '(bind-mount read-only)))))))))
 
+(test-equal "reduce-directories"
+  '("./opt/gnu/" "./opt/gnuism" "a/b/c")
+  (reduce-directories '("./opt/gnu/etc" "./opt/gnu/" "./opt/gnu/bin"
+                        "./opt/gnu/lib/debug" "./opt/gnuism" "a/b/c" "a/b/c")))
+
 (test-assert "does not pull (guix config)"
   ;; This module is meant both for the host side and "build side", so make
   ;; sure it doesn't pull in (guix config), which depends on the user's