services: guix-publish: Allow for multi-compression.

This is a followup to b8fa86adfc01205f1d942af8cb57515eb3726c52.

* guix/deprecation.scm (warn-about-deprecation): Make public.
* gnu/services/base.scm (<guix-publish-configuration>)[compression]: New
field.
[compression-level]: Default to #f.  Add '%' to getter name.
(guix-publish-configuration-compression-level): Define as deprecated.
(default-compression): New procedure.
(guix-publish-shepherd-service)[config->compression-options]: New
procedure.
Use 'match-record' instead of 'match'.
* doc/guix.texi (Base Services): Remove 'compression-level' and document
'compression'.

1 files changed, 13 insertions, 4 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index c01eb3a656..a8f3a5ad27 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -12232,10 +12232,19 @@ The TCP port to listen for connections.
 The host (and thus, network interface) to listen to.  Use
 @code{"0.0.0.0"} to listen on all the network interfaces.
 
-@item @code{compression-level} (default: @code{3})
-The gzip compression level at which substitutes are compressed.  Use
-@code{0} to disable compression altogether, and @code{9} to get the best
-compression ratio at the expense of increased CPU usage.
+@item @code{compression} (default: @code{'(("gzip" 3))})
+This is a list of compression method/level tuple used when compressing
+substitutes.  For example, to compress all substitutes with @emph{both} lzip
+at level 7 and gzip at level 9, write:
+
+@example
+'(("lzip" 7) ("gzip" 9))
+@end example
+
+Level 9 achieves the best compression ratio at the expense of increased CPU
+usage, whereas level 1 achieves fast compression.
+
+An empty list disables compression altogether.
 
 @item @code{nar-path} (default: @code{"nar"})
 The URL path at which ``nars'' can be fetched.  @xref{Invoking guix