fix enum coversion in native format for backward compatibility

dbms/src/DataTypes/DataTypeLowCardinalityHelpers.cpp

@@ -92,6 +92,9 @@ ColumnPtr recursiveLowCardinalityConversion(const ColumnPtr & column, const Data
     if (from_type->equals(*to_type))
         return column;
 
+    if (WhichDataType(to_type).isEnum() && from_type->getTypeId() == to_type->getTypeId())
+        return column;
+
     if (const auto * column_const = typeid_cast<const ColumnConst *>(column.get()))
     {
         auto & nested = column_const->getDataColumnPtr();

dbms/tests/queries/0_stateless/01035_enum_conversion_native_format.reference

+a
+a

dbms/tests/queries/0_stateless/01035_enum_conversion_native_format.sh

+#!/usr/bin/env bash
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+. $CURDIR/../shell_config.sh
+
+set -e
+
+${CLICKHOUSE_CLIENT} --query="drop table if exists enum_source;"
+${CLICKHOUSE_CLIENT} --query="drop table if exists enum_buf;"
+
+${CLICKHOUSE_CLIENT} --query="create table enum_source(e Enum8('a'=1)) engine = MergeTree order by tuple()"
+${CLICKHOUSE_CLIENT} --query="insert into enum_source values ('a')"
+${CLICKHOUSE_CLIENT} --query="create table enum_buf engine = Log as select * from enum_source;"
+${CLICKHOUSE_CLIENT} --query="alter table enum_source modify column e Enum8('a'=1, 'b'=2);"
+
+${CLICKHOUSE_CLIENT} --query="select * from enum_buf format Native" \
+    | ${CLICKHOUSE_CLIENT} --query="insert into enum_source format Native"
+
+${CLICKHOUSE_CLIENT} --query="select * from enum_source;"
+
+${CLICKHOUSE_CLIENT} --query="drop table enum_source;"
+${CLICKHOUSE_CLIENT} --query="drop table enum_buf;"