Extend the ability of planner_node_transformer_hook to store the cont…

…ext of expression being processed (#469)

Extend the ability of planner_node_transformer_hook to store the context of expression being process. This saved context will be used during planning to transform declared variable either as a Param (if it appears in TargetList) or as a const (all the other places).

Extension: babelfish-for-postgresql/babelfish_extensions#3011
Task: BABEL-5188
Signed-off-by: Dipesh Dhameliya <dddhamel@amazon.com>

src/backend/optimizer/plan/planner.c

@@ -1182,6 +1182,10 @@ preprocess_expression(PlannerInfo *root, Node *expr, int kind)
 	if (kind != EXPRKIND_RTFUNC)
 		expr = eval_const_expressions(root, expr);
 
+	/* Reset context of expression */
+	if(EXPRKIND_TARGET == kind && planner_node_transformer_hook)
+		(void) planner_node_transformer_hook(root, NULL, -1);
+
 	/*
 	 * If it's a qual or havingQual, canonicalize it.
 	 */