template<typename T> int32_t WasmBinaryWriter::startSection(T code) {
  o << uint8_t(code);
  if (sourceMap) {
    sourceMapLocationsSizeAtSectionStart = sourceMapLocations.size();
  }
  binaryLocationsSizeAtSectionStart = binaryLocations.expressions.size();
  return writeU32LEBPlaceholder(); // section size to be filled in later
}