gnu: libcanberra: Add default sounds support.

* gnu/packages/libcanberra.scm (libcanberra): Add input
  'sound-theme-freedesktop'.  Add "libcanberra-sound-theme-freedesktop.patch"
  and related phase 'patch-default-sounds-directory to patch the default
  sounds directory.

gnu/packages/libcanberra.scm

@@ -19,6 +19,7 @@
 
 (define-module (gnu packages libcanberra)
   #:use-module ((guix licenses) #:select (lgpl2.1+))
+  #:use-module (gnu packages)
   #:use-module (guix packages)
   #:use-module (guix download)
   #:use-module (guix build-system gnu)
@@ -46,7 +47,21 @@
             version ".tar.xz"))
       (sha256
        (base32
-        "0wps39h8rx2b00vyvkia5j40fkak3dpipp1kzilqla0cgvk73dn2"))))
+        "0wps39h8rx2b00vyvkia5j40fkak3dpipp1kzilqla0cgvk73dn2"))
+      ;; "sound-theme-freedesktop" is the default and fall-back sound theme for
+      ;; XDG desktops and should always be present.
+      ;; http://www.freedesktop.org/wiki/Specifications/sound-theme-spec/
+      ;; We make sure libcanberra will find it.
+      ;;
+      ;; We add the default sounds store directory to the code dealing with
+      ;; XDG_DATA_DIRS and not XDG_DATA_HOME. This is because XDG_DATA_HOME
+      ;; can only be a single directory and is inspected first.  XDG_DATA_DIRS
+      ;; can list an arbitrary number of directories and is only inspected
+      ;; later.  This is designed to allows the user to modify any theme at
+      ;; his pleasure.
+      (patch-flags '("-p0"))
+      (patches
+       (list (search-patch "libcanberra-sound-theme-freedesktop.patch")))))
     (build-system gnu-build-system)
     (inputs
      `(("alsa-lib" ,alsa-lib)
@@ -55,9 +70,21 @@
        ("libtool" ,libtool)
        ("libvorbis" ,libvorbis)
        ("pulseaudio" ,pulseaudio)
-       ("udev" ,eudev)))
+       ("udev" ,eudev)
+       ("sound-theme-freedesktop" ,sound-theme-freedesktop)))
     (native-inputs
      `(("pkg-config" ,pkg-config)))
+    (arguments
+     `(#:phases
+       (alist-cons-before
+        'build 'patch-default-sounds-directory
+        (lambda* (#:key inputs #:allow-other-keys)
+          (substitute* "src/sound-theme-spec.c"
+            (("@SOUND_THEME_DIRECTORY@")
+             (string-append
+              (assoc-ref inputs "sound-theme-freedesktop")
+              "/share"))))
+        %standard-phases)))
     (home-page "http://0pointer.de/lennart/projects/libcanberra/")
     (synopsis
      "Implementation of the XDG Sound Theme and Name Specifications")

gnu/packages/patches/libcanberra-sound-theme-freedesktop.patch

@@ -0,0 +1,22 @@
+# We insert a hook called "@SOUND_THEME_DIRECTORY@" where, at build time, we
+# insert the directory of the package "sound-theme-freedesktop" in the store.
+
+--- src/sound-theme-spec.c.orig	2015-01-11 13:13:29.520527358 +0100
++++ src/sound-theme-spec.c	2015-01-11 14:27:23.035046849 +0100
+@@ -321,9 +321,13 @@
+         const char *g;
+ 
+         if (!(g = getenv("XDG_DATA_DIRS")) || *g == 0)
+-                return "/usr/local/share:/usr/share";
+-
+-        return g;
++                return "@SOUND_THEME_DIRECTORY@";
++        else {
++                const char *stp = ":@SOUND_THEME_DIRECTORY@";
++                size_t len = strlen(stp) + strlen(g) + 1;
++                char *g2 = (char*) malloc(len);
++                return strcat(strcpy(g2, g), stp);
++        }
+ }
+ 
+ static int load_theme_dir(ca_theme_data *t, const char *name) {