message: Handle missing deps in block print
diff: @@ -37,7 +37,12 @@ static void PrintDepsTab(std::ostream& os, size_t depth, const Statement* stmt,
  if (stmt->deps.size()) {
  os << ", deps:";
  for (const auto& it : stmt->deps) {
  - os << " " << deps.at(it->get());
  + auto dep_idx_it = deps.find(it->get());
  + if (dep_idx_it != deps.end()) {
  + os << " " << dep_idx_it->second;
  + } else {
  + os << " [parent]";
  + }
  }
  }
  os << "]\n" << std::string(depth * 2, ' ');
  