v1-0001-Allow-window-functions-to-accept-a-null-treatment.patch

From 925c527b4e776d49292a0fd747dcb16357418703 Mon Sep 17 00:00:00 2001
From: Tatsuo Ishii <ishii@postgresql.org>
Date: Sun, 12 Oct 2025 16:21:40 +0900
Subject: [PATCH v1] Allow window functions to accept a null treatment clause
 by default.

Previously window functions (either built-in or user defined) should
call WinCheckAndInitializeNullTreatment with allowNullTreatment==true
if they accept a null treatment clause (RESPECT NULLS/IGNORE
NULLS). Otherwise, they are called as if null treatment clause is not
specified.

This commit changes the behavior so that window functions accept a
null treatment clause as specified without calling
WinCheckAndInitializeNullTreatment.

If window functions do not want accept a null treatment clause, call
WinCheckAndInitializeNullTreatment with allowNullTreatment==false.
---
 src/backend/executor/nodeWindowAgg.c | 17 +++++++++++------
 src/backend/utils/adt/windowfuncs.c  |  4 ----
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index e6a53f95391..c2e2ca69347 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -1303,7 +1303,8 @@ begin_partition(WindowAggState *winstate)
 			winobj->seekpos = -1;
 
 			/* reset null map */
-			if (winobj->ignore_nulls == IGNORE_NULLS)
+			if (winobj->ignore_nulls == IGNORE_NULLS ||
+				winobj->ignore_nulls == PARSER_IGNORE_NULLS)
 				memset(winobj->notnull_info, 0,
 					   NN_POS_TO_BYTES(
 									   perfuncstate->winobj->num_notnull_info));
@@ -3530,8 +3531,10 @@ put_notnull_info(WindowObject winobj, int64 pos, bool isnull)
  * WinCheckAndInitializeNullTreatment
  *		Check null treatment clause and sets ignore_nulls
  *
- * Window functions should call this to check if they are being called with
- * a null treatment clause when they don't allow it, or to set ignore_nulls.
+ * Window functions call this if they do not accept a null treatment clause
+ * with allowNullTreatment==false. It's not mandatory but they can call this
+ * with allowNullTreatment==true to explicitly stat that they accept a a null
+ * treatment clause.
  */
 void
 WinCheckAndInitializeNullTreatment(WindowObject winobj,
@@ -3555,7 +3558,6 @@ WinCheckAndInitializeNullTreatment(WindowObject winobj,
 	}
 	else if (winobj->ignore_nulls == PARSER_IGNORE_NULLS)
 		winobj->ignore_nulls = IGNORE_NULLS;
-
 }
 
 /*
@@ -3727,7 +3729,9 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 
-	null_treatment = (winobj->ignore_nulls == IGNORE_NULLS && relpos != 0);
+	null_treatment = ((winobj->ignore_nulls == IGNORE_NULLS ||
+					   winobj->ignore_nulls == PARSER_IGNORE_NULLS) &&
+					  relpos != 0);
 
 	switch (seektype)
 	{
@@ -3866,7 +3870,8 @@ WinGetFuncArgInFrame(WindowObject winobj, int argno,
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	if (winobj->ignore_nulls == IGNORE_NULLS)
+	if (winobj->ignore_nulls == IGNORE_NULLS ||
+		winobj->ignore_nulls == PARSER_IGNORE_NULLS)
 		return ignorenulls_getfuncarginframe(winobj, argno, relpos, seektype,
 											 set_mark, isnull, isout);
 
diff --git a/src/backend/utils/adt/windowfuncs.c b/src/backend/utils/adt/windowfuncs.c
index 969f02aa59b..7e936a8bfbc 100644
--- a/src/backend/utils/adt/windowfuncs.c
+++ b/src/backend/utils/adt/windowfuncs.c
@@ -541,7 +541,6 @@ leadlag_common(FunctionCallInfo fcinfo,
 	bool		isnull;
 	bool		isout;
 
-	WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
 	if (withoffset)
 	{
 		offset = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
@@ -659,7 +658,6 @@ window_first_value(PG_FUNCTION_ARGS)
 	Datum		result;
 	bool		isnull;
 
-	WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
 	result = WinGetFuncArgInFrame(winobj, 0,
 								  0, WINDOW_SEEK_HEAD, true,
 								  &isnull, NULL);
@@ -681,7 +679,6 @@ window_last_value(PG_FUNCTION_ARGS)
 	Datum		result;
 	bool		isnull;
 
-	WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
 	result = WinGetFuncArgInFrame(winobj, 0,
 								  0, WINDOW_SEEK_TAIL, true,
 								  &isnull, NULL);
@@ -705,7 +702,6 @@ window_nth_value(PG_FUNCTION_ARGS)
 	bool		isnull;
 	int32		nth;
 
-	WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
 	nth = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
 	if (isnull)
 		PG_RETURN_NULL();
-- 
2.43.0