Convert planner's AggInfo and AggTransInfo structs to proper Nodes.

This is mostly just to get outfuncs.c support for them, so that
the agginfos and aggtransinfos lists can be dumped when dumping
the contents of PlannerInfo.

While here, improve some related comments; notably, clean up
obsolete comments left over from when preprocess_minmax_aggregates
had to make its own scan of the query tree.

Discussion: https://postgr.es/m/742479.1658160504@sss.pgh.pa.us

src/backend/optimizer/plan/planagg.c

@@ -137,8 +137,8 @@ preprocess_minmax_aggregates(PlannerInfo *root)
 		return;
 
 	/*
-	 * Scan the tlist and HAVING qual to find all the aggregates and verify
+	 * Examine all the aggregates and verify all are MIN/MAX aggregates.  Stop
-	 * all are MIN/MAX aggregates.  Stop as soon as we find one that isn't.
+	 * as soon as we find one that isn't.
 	 */
 	aggs_list = NIL;
 	if (!can_minmax_aggs(root, &aggs_list))
@@ -227,24 +227,24 @@ preprocess_minmax_aggregates(PlannerInfo *root)
 
 /*
  * can_minmax_aggs
- *		Walk through all the aggregates in the query, and check
+ *		Examine all the aggregates in the query, and check if they are
- *		if they are all MIN/MAX aggregates.  If so, build a list of the
+ *		all MIN/MAX aggregates.  If so, build a list of MinMaxAggInfo
- *		distinct aggregate calls in the tree.
+ *		nodes for them.
  *
  * Returns false if a non-MIN/MAX aggregate is found, true otherwise.
- *
- * This does not descend into subqueries, and so should be used only after
- * reduction of sublinks to subplans.  There mustn't be outer-aggregate
- * references either.
  */
 static bool
 can_minmax_aggs(PlannerInfo *root, List **context)
 {
 	ListCell   *lc;
 
+	/*
+	 * This function used to have to scan the query for itself, but now we can
+	 * just thumb through the AggInfo list made by preprocess_aggrefs.
+	 */
 	foreach(lc, root->agginfos)
 	{
-		AggInfo    *agginfo = (AggInfo *) lfirst(lc);
+		AggInfo    *agginfo = lfirst_node(AggInfo, lc);
 		Aggref	   *aggref = agginfo->representative_aggref;
 		Oid			aggsortop;
 		TargetEntry *curTarget;

src/backend/optimizer/prep/prepagg.c

@@ -223,13 +223,13 @@ preprocess_aggref(Aggref *aggref, PlannerInfo *root)
 	aggno = find_compatible_agg(root, aggref, &same_input_transnos);
 	if (aggno != -1)
 	{
-		AggInfo    *agginfo = list_nth(root->agginfos, aggno);
+		AggInfo    *agginfo = list_nth_node(AggInfo, root->agginfos, aggno);
 
 		transno = agginfo->transno;
 	}
 	else
 	{
-		AggInfo    *agginfo = palloc(sizeof(AggInfo));
+		AggInfo    *agginfo = makeNode(AggInfo);
 
 		agginfo->finalfn_oid = aggfinalfn;
 		agginfo->representative_aggref = aggref;
@@ -266,7 +266,7 @@ preprocess_aggref(Aggref *aggref, PlannerInfo *root)
 										same_input_transnos);
 		if (transno == -1)
 		{
-			AggTransInfo *transinfo = palloc(sizeof(AggTransInfo));
+			AggTransInfo *transinfo = makeNode(AggTransInfo);
 
 			transinfo->args = aggref->args;
 			transinfo->aggfilter = aggref->aggfilter;
@@ -381,7 +381,7 @@ find_compatible_agg(PlannerInfo *root, Aggref *newagg,
 	aggno = -1;
 	foreach(lc, root->agginfos)
 	{
-		AggInfo    *agginfo = (AggInfo *) lfirst(lc);
+		AggInfo    *agginfo = lfirst_node(AggInfo, lc);
 		Aggref	   *existingRef;
 
 		aggno++;
@@ -452,7 +452,9 @@ find_compatible_trans(PlannerInfo *root, Aggref *newagg, bool shareable,
 	foreach(lc, transnos)
 	{
 		int			transno = lfirst_int(lc);
-		AggTransInfo *pertrans = (AggTransInfo *) list_nth(root->aggtransinfos, transno);
+		AggTransInfo *pertrans = list_nth_node(AggTransInfo,
+											   root->aggtransinfos,
+											   transno);
 
 		/*
 		 * if the transfns or transition state types are not the same then the
@@ -541,7 +543,7 @@ get_agg_clause_costs(PlannerInfo *root, AggSplit aggsplit, AggClauseCosts *costs
 
 	foreach(lc, root->aggtransinfos)
 	{
-		AggTransInfo *transinfo = (AggTransInfo *) lfirst(lc);
+		AggTransInfo *transinfo = lfirst_node(AggTransInfo, lc);
 
 		/*
 		 * Add the appropriate component function execution costs to
@@ -645,7 +647,7 @@ get_agg_clause_costs(PlannerInfo *root, AggSplit aggsplit, AggClauseCosts *costs
 
 	foreach(lc, root->agginfos)
 	{
-		AggInfo    *agginfo = (AggInfo *) lfirst(lc);
+		AggInfo    *agginfo = lfirst_node(AggInfo, lc);
 		Aggref	   *aggref = agginfo->representative_aggref;
 
 		/*

src/include/nodes/pathnodes.h

@@ -442,15 +442,15 @@ struct PlannerInfo
 	 * Information about aggregates. Filled by preprocess_aggrefs().
 	 */
 	/* AggInfo structs */
-	List	   *agginfos pg_node_attr(read_write_ignore);
+	List	   *agginfos;
 	/* AggTransInfo structs */
-	List	   *aggtransinfos pg_node_attr(read_write_ignore);
+	List	   *aggtransinfos;
-	/* number w/ DISTINCT/ORDER BY/WITHIN GROUP */
+	/* number of aggs with DISTINCT/ORDER BY/WITHIN GROUP */
-	int			numOrderedAggs pg_node_attr(read_write_ignore);
+	int			numOrderedAggs;
 	/* does any agg not support partial mode? */
-	bool		hasNonPartialAggs pg_node_attr(read_write_ignore);
+	bool		hasNonPartialAggs;
 	/* is any partial agg non-serializable? */
-	bool		hasNonSerialAggs pg_node_attr(read_write_ignore);
+	bool		hasNonSerialAggs;
 
 	/*
 	 * These fields are used only when hasRecursion is true:
@@ -3121,6 +3121,10 @@ typedef struct JoinCostWorkspace
  */
 typedef struct AggInfo
 {
+	pg_node_attr(no_copy_equal, no_read)
+
+	NodeTag		type;
+
 	/*
 	 * Link to an Aggref expr this state value is for.
 	 *
@@ -3129,6 +3133,7 @@ typedef struct AggInfo
 	 */
 	Aggref	   *representative_aggref;
 
+	/* Transition state number for this aggregate */
 	int			transno;
 
 	/*
@@ -3137,9 +3142,8 @@ typedef struct AggInfo
 	 */
 	bool		shareable;
 
-	/* Oid of the final function or InvalidOid */
+	/* Oid of the final function, or InvalidOid if none */
 	Oid			finalfn_oid;
-
 } AggInfo;
 
 /*
@@ -3151,34 +3155,40 @@ typedef struct AggInfo
  */
 typedef struct AggTransInfo
 {
+	pg_node_attr(no_copy_equal, no_read)
+
+	NodeTag		type;
+
+	/* Inputs for this transition state */
 	List	   *args;
 	Expr	   *aggfilter;
 
 	/* Oid of the state transition function */
 	Oid			transfn_oid;
 
-	/* Oid of the serialization function or InvalidOid */
+	/* Oid of the serialization function, or InvalidOid if none */
 	Oid			serialfn_oid;
 
-	/* Oid of the deserialization function or InvalidOid */
+	/* Oid of the deserialization function, or InvalidOid if none */
 	Oid			deserialfn_oid;
 
-	/* Oid of the combine function or InvalidOid */
+	/* Oid of the combine function, or InvalidOid if none */
 	Oid			combinefn_oid;
 
 	/* Oid of state value's datatype */
 	Oid			aggtranstype;
+
+	/* Additional data about transtype */
 	int32		aggtranstypmod;
 	int			transtypeLen;
 	bool		transtypeByVal;
+
+	/* Space-consumption estimate */
 	int32		aggtransspace;
 
-	/*
+	/* Initial value from pg_aggregate entry */
-	 * initial value from pg_aggregate entry
+	Datum		initValue pg_node_attr(read_write_ignore);
-	 */
-	Datum		initValue;
 	bool		initValueIsNull;
-
 } AggTransInfo;
 
 #endif							/* PATHNODES_H */