code: def _sync_binary_dep_links(self, target, gopath, lib_binary_map):
      
      required_links = set()
      for dep in target.closure():
        if dep == target:
          continue
        if not isinstance(dep, GoTarget):
          continue
        lib_binary = lib_binary_map[dep]
        lib_binary_link = os.path.join(gopath, os.path.relpath(lib_binary, self.get_gopath(dep)))
        safe_mkdir(os.path.dirname(lib_binary_link))
        if os.path.islink(lib_binary_link):
          if os.stat(lib_binary).st_mtime > os.lstat(lib_binary_link).st_mtime:
            # The binary under the link was updated after the link was created. Refresh
            # the link so the mtime (modification time) of the link is greater than the
            # mtime of the binary. This stops Go from needlessly re-compiling the library.
            os.unlink(lib_binary_link)
            os.symlink(lib_binary, lib_binary_link)
        else:
          os.symlink(lib_binary, lib_binary_link)
        required_links.add(lib_binary_link)
      self.remove_unused_links(os.path.join(gopath, 'pkg'), required_links)
docs: Syncs symlinks under gopath to the library binaries of target's transitive dependencies.
  
      :param Target target: Target whose transitive dependencies must be linked.
      :param str gopath: $GOPATH of target whose "pkg/" directory must be populated with links
                         to library binaries.
      :param dict<Target, str> lib_binary_map: Dictionary mapping a remote/local Go library to the
                                               path of the compiled binary (the ".a" file) of the
                                               library.
  
      Required links to binary dependencies under gopath's "pkg/" dir are either created if
      non-existent, or refreshed if the link is older than the underlying binary. Any pre-existing
      links within gopath's "pkg/" dir that do not correspond to a transitive dependency of target
      are deleted.