XXX: debug logging on unpack source script

Author: samueldr

modules/source.nix

@@ -188,7 +188,12 @@ let
       in mkIf (mountPoints != [])
         ((lib.concatMapStringsSep "\n" (mountPoint: "mkdir -p ${mountPoint}") mountPoints) + "\n");
 
-      unpackScript = (lib.optionalString config.enable ''
+      unpackScript =  ''
+        #
+        # ${config.src} → ${config.relpath}
+        #
+      ''
+      + (lib.optionalString config.enable ''
         mkdir -p ${config.relpath}
         ${pkgs.utillinux}/bin/mount --bind ${config.src} ${config.relpath}
       '')
@@ -269,7 +274,14 @@ in
       inherit (config.source.manifest) rev sha256;
     });
 
-    unpackScript = lib.concatMapStringsSep "\n" (d: d.unpackScript) (lib.attrValues config.source.dirs);
+    unpackScript = ''
+      (
+      PS4=" $ "
+      set -x
+    '' + lib.concatMapStringsSep "\n" (d: d.unpackScript) (lib.attrValues config.source.dirs)
+    + ''
+      )
+    '';
   };
 
   config.build = {