transformonce.patch

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 9caf1e481a2..1dcbd70a509 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -3766,30 +3766,12 @@ transformJsonArrayQueryConstructor(ParseState *pstate,
 	ResTarget  *target = makeNode(ResTarget);
 	JsonArrayAgg *agg = makeNode(JsonArrayAgg);
 	ColumnRef  *colref = makeNode(ColumnRef);
-	Query	   *query;
-	ParseState *qpstate;
-
-	/* Transform query only for counting target list entries. */
-	qpstate = make_parsestate(pstate);
-
-	query = transformStmt(qpstate, ctor->query);
-
-	if (count_nonjunk_tlist_entries(query->targetList) != 1)
-		ereport(ERROR,
-				errcode(ERRCODE_SYNTAX_ERROR),
-				errmsg("subquery must return only one column"),
-				parser_errposition(pstate, ctor->location));
-
-	free_parsestate(qpstate);
+	Node	   *transformed;
 
 	colref->fields = list_make2(makeString(pstrdup("q")),
 								makeString(pstrdup("a")));
 	colref->location = ctor->location;
 
-	/*
-	 * No formatting necessary, so set formatted_expr to be the same as
-	 * raw_expr.
-	 */
 	agg->arg = makeJsonValueExpr((Expr *) colref, (Expr *) colref,
 								 ctor->format);
 	agg->absent_on_null = ctor->absent_on_null;
@@ -3820,7 +3802,32 @@ transformJsonArrayQueryConstructor(ParseState *pstate,
 	sublink->subselect = (Node *) select;
 	sublink->location = ctor->location;
 
-	return transformExprRecurse(pstate, (Node *) sublink);
+	transformed = transformExprRecurse(pstate, (Node *) sublink);
+
+	/*
+	 * Verify that the query (which has been installed as the subselect in the
+	 * sublink) returns exactly one column after transformation.
+	 */
+	{
+		Query	   *query;
+		RangeTblEntry *rte;
+
+		query = castNode(Query, (castNode(SubLink, transformed))->subselect);
+		Assert(list_length(query->rtable) == 1);
+
+		rte = linitial_node(RangeTblEntry, query->rtable);
+		Assert(rte->rtekind == RTE_SUBQUERY);
+
+		/* Transfer our attention to the subquery */
+		query = rte->subquery;
+		if (count_nonjunk_tlist_entries(query->targetList) != 1)
+			ereport(ERROR,
+					errcode(ERRCODE_SYNTAX_ERROR),
+					errmsg("subquery must return only one column"),
+					parser_errposition(pstate, ctor->location));
+	}
+
+	return transformed;
 }
 
 /*