Adds find_recursive_union to ruleutils_15.c

Relevant PG commit:
3f50b82639637c9908afa2087de7588450aa866b

src/backend/distributed/deparser/ruleutils_15.c

@@ -341,6 +341,8 @@ static void identify_join_columns(JoinExpr *j, RangeTblEntry *jrte,
 					  deparse_columns *colinfo);
 static char *get_rtable_name(int rtindex, deparse_context *context);
 static void set_deparse_plan(deparse_namespace *dpns, Plan *plan);
+static Plan *find_recursive_union(deparse_namespace *dpns,
+								  WorkTableScan *wtscan);
 static void push_child_plan(deparse_namespace *dpns, Plan *plan,
 				deparse_namespace *save_dpns);
 static void pop_child_plan(deparse_namespace *dpns,
@@ -1779,6 +1781,9 @@ set_deparse_plan(deparse_namespace *dpns, Plan *plan)
 	 * For a SubqueryScan, pretend the subplan is INNER referent.  (We don't
 	 * use OUTER because that could someday conflict with the normal meaning.)
 	 * Likewise, for a CteScan, pretend the subquery's plan is INNER referent.
+     * For a WorkTableScan, locate the parent RecursiveUnion plan node and use
+     * that as INNER referent.
+     *
 	 * For ON CONFLICT .. UPDATE we just need the inner tlist to point to the
 	 * excluded expression's tlist. (Similar to the SubqueryScan we don't want
 	 * to reuse OUTER, it's used for RETURNING in some modify table cases,
@@ -1789,6 +1794,9 @@ set_deparse_plan(deparse_namespace *dpns, Plan *plan)
 	else if (IsA(plan, CteScan))
 		dpns->inner_plan = list_nth(dpns->subplans,
 									((CteScan *) plan)->ctePlanId - 1);
+    else if (IsA(plan, WorkTableScan))
+		dpns->inner_plan = find_recursive_union(dpns,
+												(WorkTableScan *) plan);
 	else if (IsA(plan, ModifyTable))
 		dpns->inner_plan = plan;
 	else
@@ -1812,6 +1820,29 @@ set_deparse_plan(deparse_namespace *dpns, Plan *plan)
 		dpns->index_tlist = NIL;
 }
 
+/*
+ * Locate the ancestor plan node that is the RecursiveUnion generating
+ * the WorkTableScan's work table.  We can match on wtParam, since that
+ * should be unique within the plan tree.
+ */
+static Plan *
+find_recursive_union(deparse_namespace *dpns, WorkTableScan *wtscan)
+{
+	ListCell   *lc;
+
+	foreach(lc, dpns->ancestors)
+	{
+		Plan	   *ancestor = (Plan *) lfirst(lc);
+
+		if (IsA(ancestor, RecursiveUnion) &&
+			((RecursiveUnion *) ancestor)->wtParam == wtscan->wtParam)
+			return ancestor;
+	}
+	elog(ERROR, "could not find RecursiveUnion for WorkTableScan with wtParam %d",
+		 wtscan->wtParam);
+	return NULL;
+}
+
 /*
  * push_child_plan: temporarily transfer deparsing attention to a child plan
  *
@@ -4448,9 +4479,12 @@ get_name_for_var_field(Var *var, int fieldno,
 				{
 					/*
 					 * We're deparsing a Plan tree so we don't have a CTE
-					 * list.  But the only place we'd see a Var directly
+					 * list.  But the only places we'd see a Var directly
-					 * referencing a CTE RTE is in a CteScan plan node, and we
+                     * referencing a CTE RTE are in CteScan or WorkTableScan
-					 * can look into the subplan's tlist instead.
+					 * plan nodes.  For those cases, set_deparse_plan arranged
+					 * for dpns->inner_plan to be the plan node that emits the
+					 * CTE or RecursiveUnion result, and we can look at its
+					 * tlist instead.
 					 */
 					TargetEntry *tle;
 					deparse_namespace save_dpns;