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

This is a followup to b8fa86adfc.

* 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'.

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

gnu/services/base.scm

@@ -142,7 +142,8 @@
             guix-publish-configuration-guix
             guix-publish-configuration-port
             guix-publish-configuration-host
-            guix-publish-configuration-compression-level
+            guix-publish-configuration-compression
+            guix-publish-configuration-compression-level ;deprecated
             guix-publish-configuration-nar-path
             guix-publish-configuration-cache
             guix-publish-configuration-ttl
@@ -1748,8 +1749,12 @@ archive' public keys, with GUIX."
            (default 80))
   (host    guix-publish-configuration-host        ;string
            (default "localhost"))
-  (compression-level guix-publish-configuration-compression-level ;integer
-                     (default 3))
+  (compression       guix-publish-configuration-compression
+                     (thunked)
+                     (default (default-compression this-record
+                                (current-source-location))))
+  (compression-level %guix-publish-configuration-compression-level ;deprecated
+                     (default #f))
   (nar-path    guix-publish-configuration-nar-path ;string
                (default "nar"))
   (cache       guix-publish-configuration-cache   ;#f | string
@@ -1759,10 +1764,36 @@ archive' public keys, with GUIX."
   (ttl         guix-publish-configuration-ttl     ;#f | integer
                (default #f)))
 
-(define guix-publish-shepherd-service
-  (match-lambda
-    (($ <guix-publish-configuration> guix port host compression
-                                     nar-path cache workers ttl)
+(define-deprecated (guix-publish-configuration-compression-level config)
+  "Return a compression level, the old way."
+  (match (guix-publish-configuration-compression config)
+    (((_ level) _ ...) level)))
+
+(define (default-compression config properties)
+  "Return the default 'guix publish' compression according to CONFIG, and
+raise a deprecation warning if the 'compression-level' field was used."
+  (match (%guix-publish-configuration-compression-level config)
+    (#f
+     '(("gzip" 3)))
+    (level
+     (warn-about-deprecation 'compression-level properties
+                             #:replacement 'compression)
+     `(("gzip" ,level)))))
+
+(define (guix-publish-shepherd-service config)
+  (define (config->compression-options config)
+    (match (guix-publish-configuration-compression config)
+      (()                                   ;empty list means "no compression"
+       '("-C0"))
+      (lst
+       (append-map (match-lambda
+                     ((type level)
+                      `("-C" ,(string-append type ":"
+                                             (number->string level)))))
+                   lst))))
+
+  (match-record config <guix-publish-configuration>
+    (guix port host nar-path cache workers ttl)
     (list (shepherd-service
            (provision '(guix-publish))
            (requirement '(guix-daemon))
@@ -1770,7 +1801,7 @@ archive' public keys, with GUIX."
                      (list #$(file-append guix "/bin/guix")
                            "publish" "-u" "guix-publish"
                            "-p" #$(number->string port)
-                            "-C" #$(number->string compression)
+                           #$@(config->compression-options config)
                            (string-append "--nar-path=" #$nar-path)
                            (string-append "--listen=" #$host)
                            #$@(if workers
@@ -1794,7 +1825,7 @@ archive' public keys, with GUIX."
                      (list (string-append "GUIX_LOCPATH="
                                           #$glibc-utf8-locales "/lib/locale")
                            "LC_ALL=en_US.utf8")))
-            (stop #~(make-kill-destructor)))))))
+           (stop #~(make-kill-destructor))))))
 
 (define %guix-publish-accounts
   (list (user-group (name "guix-publish") (system? #t))

guix/deprecation.scm

@@ -21,6 +21,7 @@
   #:use-module (ice-9 format)
   #:export (define-deprecated
             define-deprecated/alias
+            warn-about-deprecation
             deprecation-warning-port))
 
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