pack: Factorize base tar options.

* guix/docker.scm (%tar-determinism-options): Move to a new module and rename
to `tar-base-options'.  Adjust references accordingly.
* guix/build/pack.scm: New file.
* Makefile.am (MODULES): Register it.
* guix/scripts/pack.scm (self-contained-tarball/builder): Use it.

1 files changed, 52 insertions, 0 deletions

diff --git a/guix/build/pack.scm b/guix/build/pack.scm
new file mode 100644
index 0000000000..05c7a3c594
--- /dev/null
+++ b/guix/build/pack.scm
@@ -0,0 +1,52 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build pack)
+  #:use-module (guix build utils)
+  #:export (tar-base-options))
+
+(define* (tar-base-options #:key tar compressor)
+  "Return the base GNU tar options required to produce deterministic archives
+deterministically.  When TAR, a GNU tar command file name, is provided, the
+`--sort' option is used only if supported.  When COMPRESSOR, a command such as
+'(\"gzip\" \"-9n\"), is provided, the compressor is explicitly specified via
+the `-I' option."
+  (define (tar-supports-sort? tar)
+    (zero? (system* tar "cf" "/dev/null" "--files-from=/dev/null"
+                    "--sort=name")))
+
+  `(,@(if compressor
+          (list "-I" (string-join compressor))
+          '())
+    ;; The --sort option was added to GNU tar in version 1.28, released
+    ;; 2014-07-28.  For testing, we use the bootstrap tar, which is older
+    ;; and doesn't support it.
+    ,@(if (and=> tar tar-supports-sort?)
+          '("--sort=name")
+          '())
+    ;; Use GNU format so there's no file name length limitation.
+    "--format=gnu"
+    "--mtime=@1"
+    "--owner=root:0"
+    "--group=root:0"
+    ;; The 'nlink' of the store item files leads tar to store hard links
+    ;; instead of actual copies.  However, the 'nlink' count depends on
+    ;; deduplication in the store; it's an "implicit input" to the build
+    ;; process.  Use '--hard-dereference' to eliminate it.
+    "--hard-dereference"
+    "--check-links"))