docs: def generate_metadata_entry(self, entry_point, toolchain, spec):
          """
          After the toolchain and spec have been executed, this may be
          called to generate the artifact export entry for persistence
          into the metadata file.
          """
  
          export_target = spec['export_target']
          toolchain_bases = trace_toolchain(toolchain)
          toolchain_bin_path = spec.get(TOOLCHAIN_BIN_PATH)
          toolchain_bin = ([
              basename(toolchain_bin_path),  # bin_name
              get_bin_version_str(toolchain_bin_path),  # bin_version
          ] if toolchain_bin_path else [])
  
          return {basename(export_target): {
              'toolchain_bases': toolchain_bases,
              'toolchain_bin': toolchain_bin,
              'builder': '%s:%s' % (
                  entry_point.module_name, '.'.join(entry_point.attrs)),
          }}