From bb9f297ebf46559b294ef9a146e0bee59ec0440f Mon Sep 17 00:00:00 2001
From: Peter Geoghegan <pg@bowt.ie>
Date: Tue, 12 Nov 2024 09:33:06 -0500
Subject: [PATCH v1] Use _bt_returnitem wrapper function

---
 src/backend/access/nbtree/nbtsearch.c | 55 ++++++++++++++-------------
 1 file changed, 29 insertions(+), 26 deletions(-)

diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
index 2786a8564..b08e68e4f 100644
--- a/src/backend/access/nbtree/nbtsearch.c
+++ b/src/backend/access/nbtree/nbtsearch.c
@@ -42,6 +42,7 @@ static int	_bt_setuppostingitems(BTScanOpaque so, int itemIndex,
 static inline void _bt_savepostingitem(BTScanOpaque so, int itemIndex,
 									   OffsetNumber offnum,
 									   ItemPointer heapTid, int tupleOffset);
+static inline void _bt_returnitem(IndexScanDesc scan, BTScanOpaque so);
 static bool _bt_steppage(IndexScanDesc scan, ScanDirection dir);
 static bool _bt_readfirstpage(IndexScanDesc scan, OffsetNumber offnum,
 							  ScanDirection dir);
@@ -890,7 +891,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 	ScanKeyData notnullkeys[INDEX_MAX_KEYS];
 	int			keysz = 0;
 	StrategyNumber strat_total;
-	BTScanPosItem *currItem;
 
 	Assert(!BTScanPosIsValid(so->currPos));
 
@@ -950,7 +950,9 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 			 */
 			if (!_bt_readnextpage(scan, blkno, lastcurrblkno, dir, true))
 				return false;
-			goto readcomplete;
+
+			_bt_returnitem(scan, so);
+			return true;
 		}
 	}
 	else if (so->numArrayKeys && !so->needPrimScan)
@@ -1438,14 +1440,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 	if (!_bt_readfirstpage(scan, offnum, dir))
 		return false;
 
-readcomplete:
-	/* OK, itemIndex says what to return */
-	Assert(BTScanPosIsValid(so->currPos));
-	currItem = &so->currPos.items[so->currPos.itemIndex];
-	scan->xs_heaptid = currItem->heapTid;
-	if (scan->xs_want_itup)
-		scan->xs_itup = (IndexTuple) (so->currTuples + currItem->tupleOffset);
-
+	_bt_returnitem(scan, so);
 	return true;
 }
 
@@ -1468,7 +1463,6 @@ bool
 _bt_next(IndexScanDesc scan, ScanDirection dir)
 {
 	BTScanOpaque so = (BTScanOpaque) scan->opaque;
-	BTScanPosItem *currItem;
 
 	Assert(BTScanPosIsValid(so->currPos));
 
@@ -1493,13 +1487,7 @@ _bt_next(IndexScanDesc scan, ScanDirection dir)
 		}
 	}
 
-	/* OK, itemIndex says what to return */
-	Assert(BTScanPosIsValid(so->currPos));
-	currItem = &so->currPos.items[so->currPos.itemIndex];
-	scan->xs_heaptid = currItem->heapTid;
-	if (scan->xs_want_itup)
-		scan->xs_itup = (IndexTuple) (so->currTuples + currItem->tupleOffset);
-
+	_bt_returnitem(scan, so);
 	return true;
 }
 
@@ -1564,6 +1552,9 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum,
 	so->currPos.lsn = BufferGetLSNAtomic(so->currPos.buf);
 	so->currPos.dir = dir;
 	so->currPos.nextTupleOffset = 0;
+	/* either moreLeft or moreRight should be set, and may be unset here */
+	Assert(ScanDirectionIsForward(dir) ? so->currPos.moreRight :
+		   so->currPos.moreLeft);
 
 	PredicateLockPage(rel, so->currPos.currPage, scan->xs_snapshot);
 
@@ -2002,6 +1993,25 @@ _bt_savepostingitem(BTScanOpaque so, int itemIndex, OffsetNumber offnum,
 		currItem->tupleOffset = tupleOffset;
 }
 
+/*
+ * Return the index item from so->currPos.items[itemIndex] to the index scan
+ * via its scan descriptor
+ */
+static inline void
+_bt_returnitem(IndexScanDesc scan, BTScanOpaque so)
+{
+	BTScanPosItem *currItem = &so->currPos.items[so->currPos.itemIndex];
+
+	/* Most recent _bt_readpage must have succeeded */
+	Assert(BTScanPosIsValid(so->currPos));
+	Assert(so->currPos.itemIndex >= so->currPos.firstItem);
+	Assert(so->currPos.itemIndex <= so->currPos.lastItem);
+
+	scan->xs_heaptid = currItem->heapTid;
+	if (so->currTuples)
+		scan->xs_itup = (IndexTuple) (so->currTuples + currItem->tupleOffset);
+}
+
 /*
  *	_bt_steppage() -- Step to next page containing valid data for scan
  *
@@ -2543,7 +2553,6 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
 	Page		page;
 	BTPageOpaque opaque;
 	OffsetNumber start;
-	BTScanPosItem *currItem;
 
 	Assert(!BTScanPosIsValid(so->currPos));
 
@@ -2593,12 +2602,6 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
 	if (!_bt_readfirstpage(scan, start, dir))
 		return false;
 
-	/* OK, itemIndex says what to return */
-	Assert(BTScanPosIsValid(so->currPos));
-	currItem = &so->currPos.items[so->currPos.itemIndex];
-	scan->xs_heaptid = currItem->heapTid;
-	if (scan->xs_want_itup)
-		scan->xs_itup = (IndexTuple) (so->currTuples + currItem->tupleOffset);
-
+	_bt_returnitem(scan, so);
 	return true;
 }
-- 
2.45.2