[bug#33643] [PATCH] gnu-build-system: Enable xz to decompress in parallel.

[Christopher Baines]

It can take a little while to decompress some packages with large xz
compressed source tar files. xz includes support for parallelism, so enable
this using the parallel job count for the overall derivation.

* guix/build/gnu-build-system.scm (unpack): Set XZ_OPT to pass the -T option
to xz to enable it to work in parallel if appropriate.
---
 guix/build/gnu-build-system.scm | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/guix/build/gnu-build-system.scm b/guix/build/gnu-build-system.scm
index e5f3197b0..9d11e5b1e 100644
--- a/guix/build/gnu-build-system.scm
+++ b/guix/build/gnu-build-system.scm
@@ -147,7 +147,7 @@ chance to be set."
               locale (strerror (system-error-errno args)))
       #t)))
 
-(define* (unpack #:key source #:allow-other-keys)
+(define* (unpack #:key source parallel-build? #:allow-other-keys)
   "Unpack SOURCE in the working directory, and change directory within the
 source.  When SOURCE is a directory, copy it in a sub-directory of the current
 working directory."
@@ -161,6 +161,10 @@ working directory."
         (copy-recursively source "."
                           #:keep-mtime? #t))
       (begin
+        (when parallel-build?
+          (setenv "XZ_OPT"
+                  (format #f "-T~d" (parallel-job-count))))
+
         (if (string-suffix? ".zip" source)
             (invoke "unzip" source)
             (invoke "tar" "xvf" source))
-- 
2.19.2