message: Use `if` instead of `switch` to check MPI constants
  Most MPI constants are not guaranteed to be compile-time constants.
diff: @@ -78,15 +78,11 @@ void CheckMPIReturn(const int value, const std::string &hint)
  }
  std::string error;
  - switch (value)
  - {
  - case MPI_ERR_COMM:
  + if (value == MPI_ERR_COMM) {
  error = "MPI_ERR_COMM";
  - break;
  - case MPI_ERR_INTERN:
  + } else if (value == MPI_ERR_INTERN) {
  error = "MPI_ERR_INTERN";
  - break;
  - default:
  + } else {
  error = "MPI_ERR number: " + std::to_string(value);
  }
  