Fix btmarkpos/btrestrpos to handle array keys.

This fixes another error in commit 9e8da0f7.
I neglected to make the mark/restore functionality save and restore the
current set of array key values, which led to strange behavior if an
IndexScan with ScalarArrayOpExpr quals was used as the inner side of a
mergejoin.  Per bug #7570 from Melese Tesfaye.

src/backend/access/nbtree/nbtree.c

@@ -584,6 +584,10 @@ btmarkpos(PG_FUNCTION_ARGS)
 	else
 		so->markItemIndex = -1;
 
+	/* Also record the current positions of any array keys */
+	if (so->numArrayKeys)
+		_bt_mark_array_keys(scan);
+
 	PG_RETURN_VOID();
 }
 
@@ -596,6 +600,10 @@ btrestrpos(PG_FUNCTION_ARGS)
 	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
 	BTScanOpaque so = (BTScanOpaque) scan->opaque;
 
+	/* Restore the marked positions of any array keys */
+	if (so->numArrayKeys)
+		_bt_restore_array_keys(scan);
+
 	if (so->markItemIndex >= 0)
 	{
 		/*

src/backend/access/nbtree/nbtutils.c

@@ -595,6 +595,65 @@ _bt_advance_array_keys(IndexScanDesc scan, ScanDirection dir)
 	return found;
 }
 
+/*
+ * _bt_mark_array_keys() -- Handle array keys during btmarkpos
+ *
+ * Save the current state of the array keys as the "mark" position.
+ */
+void
+_bt_mark_array_keys(IndexScanDesc scan)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+	int			i;
+
+	for (i = 0; i < so->numArrayKeys; i++)
+	{
+		BTArrayKeyInfo *curArrayKey = &so->arrayKeys[i];
+
+		curArrayKey->mark_elem = curArrayKey->cur_elem;
+	}
+}
+
+/*
+ * _bt_restore_array_keys() -- Handle array keys during btrestrpos
+ *
+ * Restore the array keys to where they were when the mark was set.
+ */
+void
+_bt_restore_array_keys(IndexScanDesc scan)
+{
+	BTScanOpaque so = (BTScanOpaque) scan->opaque;
+	bool		changed = false;
+	int			i;
+
+	/* Restore each array key to its position when the mark was set */
+	for (i = 0; i < so->numArrayKeys; i++)
+	{
+		BTArrayKeyInfo *curArrayKey = &so->arrayKeys[i];
+		ScanKey		skey = &so->arrayKeyData[curArrayKey->scan_key];
+		int			mark_elem = curArrayKey->mark_elem;
+
+		if (curArrayKey->cur_elem != mark_elem)
+		{
+			curArrayKey->cur_elem = mark_elem;
+			skey->sk_argument = curArrayKey->elem_values[mark_elem];
+			changed = true;
+		}
+	}
+
+	/*
+	 * If we changed any keys, we must redo _bt_preprocess_keys.  That might
+	 * sound like overkill, but in cases with multiple keys per index column
+	 * it seems necessary to do the full set of pushups.
+	 */
+	if (changed)
+	{
+		_bt_preprocess_keys(scan);
+		/* The mark should have been set on a consistent set of keys... */
+		Assert(so->qual_ok);
+	}
+}
+
 
 /*
  *	_bt_preprocess_keys() -- Preprocess scan keys

src/include/access/nbtree.h

@@ -535,6 +535,7 @@ typedef struct BTArrayKeyInfo
 {
 	int			scan_key;		/* index of associated key in arrayKeyData */
 	int			cur_elem;		/* index of current element in elem_values */
+	int			mark_elem;		/* index of marked element in elem_values */
 	int			num_elems;		/* number of elems in current array value */
 	Datum	   *elem_values;	/* array of num_elems Datums */
 } BTArrayKeyInfo;
@@ -665,6 +666,8 @@ extern void _bt_freestack(BTStack stack);
 extern void _bt_preprocess_array_keys(IndexScanDesc scan);
 extern void _bt_start_array_keys(IndexScanDesc scan, ScanDirection dir);
 extern bool _bt_advance_array_keys(IndexScanDesc scan, ScanDirection dir);
+extern void _bt_mark_array_keys(IndexScanDesc scan);
+extern void _bt_restore_array_keys(IndexScanDesc scan);
 extern void _bt_preprocess_keys(IndexScanDesc scan);
 extern IndexTuple _bt_checkkeys(IndexScanDesc scan,
 			  Page page, OffsetNumber offnum,