code: function(src) {
      var cache;
  
      try {
        cache = fs.existsSync(src) ? file.readJSON(src) : undefined;
      } catch (e) {
        debug(e);
      }
  
      // Progressively upgrade `cache`, which is one of:
      // empty
      // {}
      // { file: size [,...] }
      // { "": { tips: { label: SHA1, ... } }, label: { file: size, ... }, ... }
      // { "": { version: 0.4, tips: { label: SHA1, ... } },
      //   label: { file: { "": size, compressor: size, ... }, ... }, ... }
      if (typeof cache !== "object") {
        cache = undefined;
      }
      if (!cache || !cache[""]) {
        // If promoting cache to dictionary, assume that data are for last run
        cache = _.zipObject(["", lastrun], [{ version: 0, tips: {} }, cache]);
      }
      if (!cache[""].version) {
        cache[""].version = 0.4;
        _.forEach(cache, function(sizes, label) {
          if (!label || !sizes) {
            return;
          }
  
          // If promoting sizes to dictionary, assume that compressed size data are indicated by suffixes
          Object.keys(sizes)
            .sort()
            .forEach(function(file) {
              var parts = file.split("."),
                prefix = parts.shift();
  
              // Append compressed size data to a matching prefix
              while (parts.length) {
                if (typeof sizes[prefix] === "object") {
                  sizes[prefix][parts.join(".")] = sizes[file];
                  delete sizes[file];
                  return;
                }
                prefix += "." + parts.shift();
              }
  
              // Store uncompressed size data
              sizes[file] = { "": sizes[file] };
            });
        });
      }
  
      return cache;
    }
docs: Size cache helper