function mergeData(data, source) {
      var bitmask = data[1],
          srcBitmask = source[1],
          newBitmask = bitmask | srcBitmask,
          isCommon = newBitmask < (WRAP_BIND_FLAG | WRAP_BIND_KEY_FLAG | WRAP_ARY_FLAG);

      var isCombo =
        ((srcBitmask == WRAP_ARY_FLAG) && (bitmask == WRAP_CURRY_FLAG)) ||
        ((srcBitmask == WRAP_ARY_FLAG) && (bitmask == WRAP_REARG_FLAG) && (data[7].length <= source[8])) ||
        ((srcBitmask == (WRAP_ARY_FLAG | WRAP_REARG_FLAG)) && (source[7].length <= source[8]) && (bitmask == WRAP_CURRY_FLAG));

      // Exit early if metadata can't be merged.
      if (!(isCommon || isCombo)) {
        return data;
      }
      // Use source `thisArg` if available.
      if (srcBitmask & WRAP_BIND_FLAG) {
        data[2] = source[2];
        // Set when currying a bound function.
        newBitmask |= bitmask & WRAP_BIND_FLAG ? 0 : WRAP_CURRY_BOUND_FLAG;
      }
      // Compose partial arguments.
      var value = source[3];
      if (value) {
        var partials = data[3];
        data[3] = partials ? composeArgs(partials, value, source[4]) : value;
        data[4] = partials ? replaceHolders(data[3], PLACEHOLDER) : source[4];
      }
      // Compose partial right arguments.
      value = source[5];
      if (value) {
        partials = data[5];
        data[5] = partials ? composeArgsRight(partials, value, source[6]) : value;
        data[6] = partials ? replaceHolders(data[5], PLACEHOLDER) : source[6];
      }
      // Use source `argPos` if available.
      value = source[7];
      if (value) {
        data[7] = value;
      }
      // Use source `ary` if it's smaller.
      if (srcBitmask & WRAP_ARY_FLAG) {
        data[8] = data[8] == null ? source[8] : nativeMin(data[8], source[8]);
      }
      // Use source `arity` if one is not provided.
      if (data[9] == null) {
        data[9] = source[9];
      }
      // Use source `func` and merge bitmasks.
      data[0] = source[0];
      data[1] = newBitmask;

      return data;
    }
Merges the function metadata of `source` into `data`.

Merging metadata reduces the number of wrappers used to invoke a function.
This is possible because methods like `_.bind`, `_.curry`, and `_.partial`
may be applied regardless of execution order. Methods like `_.ary` and
`_.rearg` modify function arguments, making the order in which they are
executed important, preventing the merging of metadata. However, we make
an exception for a safe combined case where curried functions have `_.ary`
and or `_.rearg` applied.

@private
@param {Array} data The destination metadata.
@param {Array} source The source metadata.
@returns {Array} Returns `data`.