anchor.diff:      pathExists
       readFile
       ;
  -in
  -rec {
   
     # Returns the type of a path: regular (for file), symlink, or directory
     pathType = p: getAttr (baseNameOf p) (readDir (dirOf p));
  
positive.code:   pathHasContext = builtins.hasContext or (lib.hasPrefix storeDir);
  
    canCleanSource = src: src ? _isLibCleanSourceWith || !(pathHasContext (toString src));
  }
  
negative.code:   #
    cleanSourceWith = { filter ? _path: _type: true, src, name ? null }:
      let
        orig = toSourceAttributes src;
      in fromSourceAttributes {
        inherit (orig) origSrc;
        filter = path: type: filter path type && orig.filter path type;
        name = if name != null then name else orig.name;
      };
  
    # Filter sources by a list of regular expressions.
  