services: pulseaudio: Add an extra-script-files configuration field.

* gnu/services/sound.scm (<pulseaudio-configuration>)
[extra-script-files]: Add field.
(extra-script-files->file-union): New procedure.
(append-include-directive): Likewise.
(pulseaudio-etc): Use them.
* doc/guix.texi: Document the new 'extra-script-files- configuration field.

doc/guix.texi

@@ -21511,11 +21511,44 @@ List of settings to set in @file{daemon.conf}, formatted just like
 @var{client-conf}.
 
 @item @code{script-file} (default: @code{(file-append pulseaudio "/etc/pulse/default.pa")})
-Script file to use as @file{default.pa}.
+Script file to use as @file{default.pa}.  In case the
+@code{extra-script-files} field below is used, an @code{.include}
+directive pointing to @file{/etc/pulse/default.pa.d} is appended to the
+provided script.
+
+@item @code{extra-script-files} (default: @code{'())})
+A list of file-like objects defining extra PulseAudio scripts to run at
+the initialization of the @command{pulseaudio} daemon, after the main
+@code{script-file}.  The scripts are deployed to the
+@file{/etc/pulse/default.pa.d} directory; they should have the
+@samp{.pa} file name extension.  For a reference of the available
+commands, refer to @command{man pulse-cli-syntax}.
 
 @item @code{system-script-file} (default: @code{(file-append pulseaudio "/etc/pulse/system.pa")})
 Script file to use as @file{system.pa}.
 @end table
+
+The example below sets the default PulseAudio card profile, the default
+sink and the default source to use for a old SoundBlaster Audigy sound
+card:
+@lisp
+(pulseaudio-configuration
+ (extra-script-files
+  (list (plain-file "audigy.pa"
+                    (string-append "\
+set-card-profile alsa_card.pci-0000_01_01.0 \
+  output:analog-surround-40+input:analog-mono
+set-default-source alsa_input.pci-0000_01_01.0.analog-mono
+set-default-sink alsa_output.pci-0000_01_01.0.analog-surround-40\n")))))
+@end lisp
+
+Note that @code{pulseaudio-service-type} is part of
+@code{%desktop-services}; if your operating system declaration was
+derived from one of the desktop templates, you'll want to adjust the
+above example to modify the existing @code{pulseaudio-service-type} via
+@code{modify-services} (@pxref{Service Reference,
+@code{modify-services}}), instead of defining a new one.
+
 @end deftp
 
 @deffn {Scheme Variable} ladspa-service-type

gnu/services/sound.scm

@@ -26,14 +26,17 @@ (define-module (gnu services sound)
   #:use-module (gnu services)
   #:use-module (gnu system pam)
   #:use-module (gnu system shadow)
+  #:use-module (guix diagnostics)
   #:use-module (guix gexp)
   #:use-module (guix packages)
   #:use-module (guix records)
   #:use-module (guix store)
+  #:use-module (guix ui)
   #:use-module (gnu packages audio)
   #:use-module (gnu packages linux)
   #:use-module (gnu packages pulseaudio)
   #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
   #:export (alsa-configuration
             alsa-service-type
 
@@ -125,6 +128,8 @@ (define-record-type* <pulseaudio-configuration>
                (default '((flat-volumes . no))))
   (script-file pulseaudio-configuration-script-file
                (default (file-append pulseaudio "/etc/pulse/default.pa")))
+  (extra-script-files pulseaudio-configuration-extra-script-files
+                      (default '()))
   (system-script-file pulseaudio-configuration-system-script-file
                       (default
                         (file-append pulseaudio "/etc/pulse/system.pa"))))
@@ -145,14 +150,60 @@ (define pulseaudio-environment
        ("PULSE_CLIENTCONFIG" . ,(apply mixed-text-file "client.conf"
                                        (map pulseaudio-conf-entry client-conf)))))))
 
+(define (extra-script-files->file-union extra-script-files)
+  "Return a G-exp obtained by processing EXTRA-SCRIPT-FILES with FILE-UNION."
+
+  (define (file-like->name file)
+    (match file
+      ((? local-file?)
+       (local-file-name file))
+      ((? plain-file?)
+       (plain-file-name file))
+      ((? computed-file?)
+       (computed-file-name file))
+      (_ (leave (G_ "~a is not a local-file, plain-file or \
+computed-file object~%") file))))
+
+  (define (assert-pulseaudio-script-file-name name)
+    (unless (string-suffix? ".pa" name)
+      (leave (G_ "`~a' lacks the required `.pa' file name extension~%") name))
+    name)
+
+  (let ((labels (map (compose assert-pulseaudio-script-file-name
+                              file-like->name)
+                     extra-script-files)))
+    (file-union "default.pa.d" (zip labels extra-script-files))))
+
+(define (append-include-directive script-file)
+  "Append an include directive to source scripts under /etc/pulse/default.pa.d."
+  (computed-file "default.pa"
+                 #~(begin
+                     (use-modules (ice-9 textual-ports))
+                     (define script-text
+                       (call-with-input-file #$script-file get-string-all))
+                     (call-with-output-file #$output
+                       (lambda (port)
+                         (format port (string-append script-text "
+### Added by Guix to include scripts specified in extra-script-files.
+.nofail
+.include /etc/pulse/default.pa.d~%")))))))
+
 (define pulseaudio-etc
   (match-lambda
-    (($ <pulseaudio-configuration> _ _ default-script-file system-script-file)
+    (($ <pulseaudio-configuration> _ _ default-script-file extra-script-files
+                                   system-script-file)
      `(("pulse"
         ,(file-union
           "pulse"
-          `(("default.pa" ,default-script-file)
-            ("system.pa" ,system-script-file))))))))
+          `(("default.pa"
+             ,(if (null? extra-script-files)
+                  default-script-file
+                  (append-include-directive default-script-file)))
+            ("system.pa" ,system-script-file)
+            ,@(if (null? extra-script-files)
+                  '()
+                  `(("default.pa.d" ,(extra-script-files->file-union
+                                      extra-script-files)))))))))))
 
 (define pulseaudio-service-type
   (service-type