code: func (i *IndexFile) Merge(f *IndexFile) {
  	for _, cvs := range f.Entries {
  		for _, cv := range cvs {
  			if !i.Has(cv.Name, cv.Version) {
  				e := i.Entries[cv.Name]
  				i.Entries[cv.Name] = append(e, cv)
  			}
  		}
  	}
  }
docs: // Merge merges the given index file into this index.
  //
  // This merges by name and version.
  //
  // If one of the entries in the given index does _not_ already exist, it is added.
  // In all other cases, the existing record is preserved.
  //
  // This can leave the index in an unsorted state