gnu: Add compression module.

Move the compression record to a dedicated module so that it can be used
outside (guix scripts pack) module.

* guix/scripts/pack.scm (<compressor>, %compressors, lookup-compressor): Move
it to ...
* gnu/compression.scm: ... this new file.
* gnu/ci.scm: Adapt it.
* local.mk (GNU_SYSTEM_MODULES): Add it.

3 files changed, 72 insertions, 1 deletions

diff --git a/gnu/ci.scm b/gnu/ci.scm
index 2c51ea7387e..19a48bdbf11 100644
--- a/gnu/ci.scm
+++ b/gnu/ci.scm
@@ -39,9 +39,10 @@
                 #:select (gpl3+ license? license-name))
   #:use-module ((guix utils) #:select (%current-system))
   #:use-module ((guix scripts pack)
-                #:select (lookup-compressor self-contained-tarball))
+                #:select (self-contained-tarball))
   #:use-module (gnu bootloader)
   #:use-module (gnu bootloader u-boot)
+  #:use-module (gnu compression)
   #:use-module (gnu image)
   #:use-module (gnu packages)
   #:use-module (gnu packages gcc)
diff --git a/gnu/compression.scm b/gnu/compression.scm
new file mode 100644
index 00000000000..0418e80a158
--- /dev/null
+++ b/gnu/compression.scm
@@ -0,0 +1,69 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2022 Mathieu Othacehe <othacehe@gnu.org>
+;;;
+;;; 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 (gnu compression)
+  #:use-module (guix gexp)
+  #:use-module (guix ui)
+  #:use-module ((gnu packages compression) #:hide (zip))
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (ice-9 match)
+  #:export (compressor
+            compressor?
+            compressor-name
+            compressor-extension
+            compressor-command
+            %compressors
+            lookup-compressor))
+
+;; Type of a compression tool.
+(define-record-type <compressor>
+  (compressor name extension command)
+  compressor?
+  (name       compressor-name)      ;string (e.g., "gzip")
+  (extension  compressor-extension) ;string (e.g., ".lz")
+  (command    compressor-command))  ;gexp (e.g., #~(list "/gnu/store/…/gzip"
+                                    ;                    "-9n" ))
+
+(define %compressors
+  ;; Available compression tools.
+  (list (compressor "gzip"  ".gz"
+                    #~(list #+(file-append gzip "/bin/gzip") "-9n"))
+        (compressor "lzip"  ".lz"
+                    #~(list #+(file-append lzip "/bin/lzip") "-9"))
+        (compressor "xz"    ".xz"
+                    #~(append (list #+(file-append xz "/bin/xz")
+                                    "-e")
+                              (%xz-parallel-args)))
+        (compressor "bzip2" ".bz2"
+                    #~(list #+(file-append bzip2 "/bin/bzip2") "-9"))
+        (compressor "zstd" ".zst"
+                    ;; The default level 3 compresses better than gzip in a
+                    ;; fraction of the time, while the highest level 19
+                    ;; (de)compresses more slowly and worse than xz.
+                    #~(list #+(file-append zstd "/bin/zstd") "-3"))
+        (compressor "none" "" #f)))
+
+(define (lookup-compressor name)
+  "Return the compressor object called NAME.  Error out if it could not be
+found."
+  (or (find (match-lambda
+              (($ <compressor> name*)
+               (string=? name* name)))
+            %compressors)
+      (leave (G_ "~a: compressor not found~%") name)))
diff --git a/gnu/local.mk b/gnu/local.mk
index 140845a7c69..4774be26883 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -81,6 +81,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/bootloader/u-boot.scm                     \
   %D%/bootloader/depthcharge.scm                \
   %D%/ci.scm                                    \
+  %D%/compression.scm                           \
   %D%/home.scm                                  \
   %D%/home/services.scm                 \
   %D%/home/services/desktop.scm                 \