Backport #19064 to 20.12: Restrict MODIFY TTL for tables created in old syntax

src/Storages/MergeTree/MergeTreeData.cpp

@@ -1491,6 +1491,12 @@ void MergeTreeData::checkAlterIsPossible(const AlterCommands & commands, const S
                 "ALTER MODIFY ORDER BY is not supported for default-partitioned tables created with the old syntax",
                 ErrorCodes::BAD_ARGUMENTS);
         }
+        if (command.type == AlterCommand::MODIFY_TTL && !is_custom_partitioned)
+        {
+            throw Exception(
+                "ALTER MODIFY TTL is not supported for default-partitioned tables created with the old syntax",
+                ErrorCodes::BAD_ARGUMENTS);
+        }
         if (command.type == AlterCommand::MODIFY_SAMPLE_BY)
         {
             if (!is_custom_partitioned)

tests/queries/0_stateless/01652_ttl_old_syntax.sql

+DROP TABLE IF EXISTS ttl_old_syntax;
+
+CREATE TABLE ttl_old_syntax (d Date, i Int) ENGINE = MergeTree(d, i, 8291);
+ALTER TABLE ttl_old_syntax MODIFY TTL toDate('2020-01-01'); -- { serverError 36 }
+
+DROP TABLE ttl_old_syntax;