makeFontsConf: accept 'includes'

Lets you add pure font configuration without having to copy/paste the
whole generated config.

pkgs/development/libraries/fontconfig/make-fonts-conf.nix

@@ -4,7 +4,7 @@ let fontconfig_ = fontconfig; in
 {
   fontconfig ? fontconfig_
   # an array of fonts, e.g. `[ pkgs.dejavu_fonts.minimal ]`
-,  fontDirectories
+  ,  fontDirectories
   , impureFontDirectories ? [
     # nix user profile
     "~/.nix-profile/lib/X11/fonts" "~/.nix-profile/share/fonts"
@@ -18,19 +18,23 @@ let fontconfig_ = fontconfig; in
   ++ lib.optionals stdenv.isDarwin [ "/Library/Fonts" "/System/Library/Fonts" ]
   # nix default profile
   ++ [ "/nix/var/nix/profiles/default/lib/X11/fonts" "/nix/var/nix/profiles/default/share/fonts" ]
+
+  # to include custom config
+  , includes ? ["/etc/fonts/conf.d"]
 }:
 
 runCommand "fonts.conf"
   {
     nativeBuildInputs = [ libxslt ];
     buildInputs = [ fontconfig ];
-    inherit fontDirectories;
+    inherit fontDirectories includes;
     # Add a default font for non-nixos systems, <1MB and in nixos defaults.
     impureFontDirectories = impureFontDirectories ++ [ dejavu_fonts.minimal ];
   }
   ''
     xsltproc --stringparam fontDirectories "$fontDirectories" \
       --stringparam impureFontDirectories "$impureFontDirectories" \
+      --stringparam includes "$includes" \
       --path ${fontconfig.out}/share/xml/fontconfig \
       ${./make-fonts-conf.xsl} ${fontconfig.out}/etc/fonts/fonts.conf \
       > $out

pkgs/development/libraries/fontconfig/make-fonts-conf.xsl

@@ -16,6 +16,7 @@
 
   <xsl:param name="fontDirectories" />
   <xsl:param name="impureFontDirectories" />
+  <xsl:param name="includes" />
 
   <xsl:template match="/fontconfig">
 
@@ -30,8 +31,10 @@
       <xsl:text>&#0010;</xsl:text>
 
       <!-- system-wide config -->
-      <include ignore_missing="yes">/etc/fonts/conf.d</include>
-      <xsl:text>&#0010;</xsl:text>
+      <xsl:for-each select="str:tokenize($includes)">
+        <include ignore_missing="yes"><xsl:value-of select="." /></include>
+        <xsl:text>&#0010;</xsl:text>
+      </xsl:for-each>
 
       <dir prefix="xdg">fonts</dir>
       <xsl:text>&#0010;</xsl:text>