code: func ToPBFieldType(ft *types.FieldType) *tipb.FieldType {
  	return &tipb.FieldType{
  		Tp:      int32(ft.Tp),
  		Flag:    uint32(ft.Flag),
  		Flen:    int32(ft.Flen),
  		Decimal: int32(ft.Decimal),
  		Charset: ft.Charset,
  		Collate: collationToProto(ft.Collate),
  	}
  }
docs: // ToPBFieldType converts *types.FieldType to *tipb.FieldType.