Throw an error if there is a RangeTblEntry that is not assigned an RTE identity. (#6295)

* Fix issue : 6109 Segfault or (assertion failure) is possible when using a SQL function

* DESCRIPTION: Ensures disallowing the usage of SQL functions referencing to a distributed table and prevents a segfault.
Using a SQL function may result in segmentation fault in some cases.
This change fixes the issue by throwing an error message when a SQL function cannot be handled.

Fixes #6109.

* DESCRIPTION: Ensures disallowing the usage of SQL functions referencing to a distributed table and prevents a segfault.
Using a SQL function may result in segmentation fault in some cases. This change fixes the issue by throwing an error message when a SQL function cannot be handled.

Fixes #6109.

Co-authored-by: Emel Simsek <emel.simsek@microsoft.com>

src/backend/distributed/planner/distributed_planner.c

@@ -559,9 +559,26 @@ int
 GetRTEIdentity(RangeTblEntry *rte)
 {
 	Assert(rte->rtekind == RTE_RELATION);
-	Assert(rte->values_lists != NIL);
+
+	/*
+	 * Since SQL functions might be in-lined by standard_planner,
+	 * we might miss assigning an RTE identity for RangeTblEntries
+	 * related to SQL functions. We already have checks in other
+	 * places to throw an error for SQL functions but they are not
+	 * sufficient due to function in-lining; so here we capture such
+	 * cases and throw an error here.
+	 */
+	if (list_length(rte->values_lists) != 2)
+	{
+		ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						errmsg("cannot perform distributed planning on this "
+							   "query because parameterized queries for SQL "
+							   "functions referencing distributed tables are "
+							   "not supported"),
+						errhint("Consider using PL/pgSQL functions instead.")));
+	}
+
 	Assert(IsA(rte->values_lists, IntList));
-	Assert(list_length(rte->values_lists) == 2);
 
 	return linitial_int(rte->values_lists);
 }

src/test/regress/expected/multi_sql_function.out

@@ -320,6 +320,9 @@ INSERT INTO test_parameterized_sql VALUES(1, 1);
 SELECT * FROM test_parameterized_sql_function(1);
 ERROR:  cannot perform distributed planning on this query because parameterized queries for SQL functions referencing distributed tables are not supported
 HINT:  Consider using PL/pgSQL functions instead.
+SELECT (SELECT 1 FROM test_parameterized_sql limit 1) FROM test_parameterized_sql_function(1);
+ERROR:  cannot perform distributed planning on this query because parameterized queries for SQL functions referencing distributed tables are not supported
+HINT:  Consider using PL/pgSQL functions instead.
 SELECT test_parameterized_sql_function_in_subquery_where(1);
 ERROR:  could not create distributed plan
 DETAIL:  Possibly this is caused by the use of parameters in SQL functions, which is not supported in Citus.

src/test/regress/sql/multi_sql_function.sql

@@ -144,6 +144,9 @@ INSERT INTO test_parameterized_sql VALUES(1, 1);
 
 -- all of them should fail
 SELECT * FROM test_parameterized_sql_function(1);
+
+SELECT (SELECT 1 FROM test_parameterized_sql limit 1) FROM test_parameterized_sql_function(1);
+
 SELECT test_parameterized_sql_function_in_subquery_where(1);
 
 -- postgres behaves slightly differently for the following