Fix Var handling for Vars of different level in constify_now

This patch fixes the constify_now optimization to ignore Vars of
different level. Previously this could potentially lead to an
assertion failure cause the varno of that varno might be bigger
than the number of entries in the rangetable. Found by sqlsmith.

src/planner/constify_now.c

@@ -60,6 +60,8 @@ is_valid_now_expr(OpExpr *op, List *rtable)
 	 * because that will be the time column.
 	 */
 	Var *var = linitial_node(Var, op->args);
+	if (var->varlevelsup != 0)
+		return false;
 	Assert(var->varno <= list_length(rtable));
 	RangeTblEntry *rte = list_nth(rtable, var->varno - 1);
 

src/planner/planner.c

@@ -293,7 +293,7 @@ preprocess_query(Node *node, PreprocessQueryContext *context)
 	if (node == NULL)
 		return false;
 
-	if (ts_guc_enable_now_constify && IsA(node, FromExpr))
+	if (IsA(node, FromExpr) && ts_guc_enable_optimizations && ts_guc_enable_now_constify)
 	{
 		FromExpr *from = castNode(FromExpr, node);
 		if (from->quals)

tsl/test/shared/expected/constify_now-12.out

@@ -469,3 +469,21 @@ EXECUTE p1;
 (2 rows)
 
 DROP TABLE prep_const_now;
+-- test outer var references dont trip up constify_now
+-- no optimization is done in this case
+:PREFIX SELECT * FROM
+  metrics_tstz m1
+  INNER JOIN metrics_tstz as m2 on (true)
+WHERE
+  EXISTS (SELECT * FROM metrics_tstz AS m3 WHERE m2.time > now());
+QUERY PLAN
+ Nested Loop
+   ->  Seq Scan on _hyper_X_X_chunk m1
+   ->  Materialize
+         ->  Nested Loop Semi Join
+               ->  Index Scan using _hyper_X_X_chunk_metrics_tstz_time_idx on _hyper_X_X_chunk m2
+                     Index Cond: ("time" > now())
+               ->  Materialize
+                     ->  Seq Scan on _hyper_X_X_chunk m3
+(8 rows)
+

tsl/test/shared/expected/constify_now-13.out

@@ -469,3 +469,21 @@ EXECUTE p1;
 (2 rows)
 
 DROP TABLE prep_const_now;
+-- test outer var references dont trip up constify_now
+-- no optimization is done in this case
+:PREFIX SELECT * FROM
+  metrics_tstz m1
+  INNER JOIN metrics_tstz as m2 on (true)
+WHERE
+  EXISTS (SELECT * FROM metrics_tstz AS m3 WHERE m2.time > now());
+QUERY PLAN
+ Nested Loop
+   ->  Seq Scan on _hyper_X_X_chunk m1
+   ->  Materialize
+         ->  Nested Loop Semi Join
+               ->  Index Scan using _hyper_X_X_chunk_metrics_tstz_time_idx on _hyper_X_X_chunk m2
+                     Index Cond: ("time" > now())
+               ->  Materialize
+                     ->  Seq Scan on _hyper_X_X_chunk m3
+(8 rows)
+

tsl/test/shared/expected/constify_now-14.out

@@ -468,3 +468,21 @@ EXECUTE p1;
 (2 rows)
 
 DROP TABLE prep_const_now;
+-- test outer var references dont trip up constify_now
+-- no optimization is done in this case
+:PREFIX SELECT * FROM
+  metrics_tstz m1
+  INNER JOIN metrics_tstz as m2 on (true)
+WHERE
+  EXISTS (SELECT * FROM metrics_tstz AS m3 WHERE m2.time > now());
+QUERY PLAN
+ Nested Loop
+   ->  Seq Scan on _hyper_X_X_chunk m1
+   ->  Materialize
+         ->  Nested Loop Semi Join
+               ->  Index Scan using _hyper_X_X_chunk_metrics_tstz_time_idx on _hyper_X_X_chunk m2
+                     Index Cond: ("time" > now())
+               ->  Materialize
+                     ->  Seq Scan on _hyper_X_X_chunk m3
+(8 rows)
+

tsl/test/shared/sql/constify_now.sql.in

@@ -104,3 +104,12 @@ SET timescaledb.current_timestamp_mock TO '3002-01-01';
 EXECUTE p1;
 
 DROP TABLE prep_const_now;
+
+-- test outer var references dont trip up constify_now
+-- no optimization is done in this case
+:PREFIX SELECT * FROM
+  metrics_tstz m1
+  INNER JOIN metrics_tstz as m2 on (true)
+WHERE
+  EXISTS (SELECT * FROM metrics_tstz AS m3 WHERE m2.time > now());
+