Maybe we should forbid subqueries as function arguments on parser level? We can allow it for table functions only by passing special flag (something like is_table_function) to ParserFunction constructor from ParserTableExpression::parseImpl(...), ParserCreateTableQuery::parseImpl(...) and similar places.

Maybe we should forbid subqueries as function arguments on parser level? We can allow it for table functions only by passing special flag (something like is_table_function) to ParserFunction constructor from ParserTableExpression::parseImpl(...), ParserCreateTableQuery::parseImpl(...) and similar places.

Good idea! Actually we only need to do that for ParserTableExpression.

There are still places where expression parser is used directly, for instance, select * from remote('127.0.0.1:9000', system.numbers, view(select 1)). https://clickhouse-test-reports.s3.yandex.net/21401/909cb3c24324e923a371255e01cbba6f0730b854/fuzzer_debug/fuzzer.log

We still need a guard in ASTFunction.