PGPRO-1572: Fix crash on empty table using index scan

Author: za-arthur

Diff for: expected/rum.out

@@ -4,6 +4,18 @@ CREATE TRIGGER tsvectorupdate
 BEFORE UPDATE OR INSERT ON test_rum
 FOR EACH ROW EXECUTE PROCEDURE tsvector_update_trigger('a', 'pg_catalog.english', 't');
 CREATE INDEX rumidx ON test_rum USING rum (a rum_tsvector_ops);
+-- Check empty table using index scan
+SELECT
+	a <=> to_tsquery('pg_catalog.english', 'way & (go | half)'),
+	rum_ts_distance(a, to_tsquery('pg_catalog.english', 'way & (go | half)')),
+	*
+	FROM test_rum
+	ORDER BY a <=> to_tsquery('pg_catalog.english', 'way & (go | half)') limit 2;
+ ?column? | rum_ts_distance | t | a 
+----------+-----------------+---+---
+(0 rows)
+
+-- Fill the table with data
 \copy test_rum(t) from 'data/rum.data';
 CREATE INDEX failed_rumidx ON test_rum USING rum (a rum_tsvector_addon_ops);
 ERROR:  additional information attribute "a" is not found in index

Diff for: sql/rum.sql

@@ -7,6 +7,15 @@ BEFORE UPDATE OR INSERT ON test_rum
 FOR EACH ROW EXECUTE PROCEDURE tsvector_update_trigger('a', 'pg_catalog.english', 't');
 CREATE INDEX rumidx ON test_rum USING rum (a rum_tsvector_ops);
 
+-- Check empty table using index scan
+SELECT
+	a <=> to_tsquery('pg_catalog.english', 'way & (go | half)'),
+	rum_ts_distance(a, to_tsquery('pg_catalog.english', 'way & (go | half)')),
+	*
+	FROM test_rum
+	ORDER BY a <=> to_tsquery('pg_catalog.english', 'way & (go | half)') limit 2;
+
+-- Fill the table with data
 \copy test_rum(t) from 'data/rum.data';
 
 CREATE INDEX failed_rumidx ON test_rum USING rum (a rum_tsvector_addon_ops);

Diff for: src/rumget.c

@@ -609,7 +609,17 @@ startScanEntry(RumState * rumstate, RumScanEntry entry, Snapshot snapshot)
 			 (entry->queryCategory == RUM_CAT_EMPTY_QUERY &&
 			  entry->scanWithAddInfo))
 	{
-		IndexTuple	itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, stackEntry->off));
+		IndexTuple	itup;
+		ItemId		itemid = PageGetItemId(page, stackEntry->off);
+
+		/*
+		 * We don't want to crash if line pointer is not used.
+		 */
+		if (entry->queryCategory == RUM_CAT_EMPTY_QUERY &&
+			!ItemIdHasStorage(itemid))
+			goto endScanEntry;
+
+		itup = (IndexTuple) PageGetItem(page, itemid);
 
 		if (RumIsPostingTree(itup))
 		{
@@ -689,6 +699,7 @@ startScanEntry(RumState * rumstate, RumScanEntry entry, Snapshot snapshot)
 		SCAN_ENTRY_GET_KEY(entry, rumstate, itup);
 	}
 
+endScanEntry:
 	if (needUnlock)
 		LockBuffer(stackEntry->buffer, RUM_UNLOCK);
 	if (entry->stack == NULL)
@@ -2043,8 +2054,12 @@ scanGetItemFull(IndexScanDesc scan, RumItem *advancePast,
 	 */
 	entry = so->entries[0];
 
+	if (entry->isFinished)
+		return false;
+
 	entryGetItem(&so->rumstate, entry, &nextEntryList, scan->xs_snapshot);
-	if (entry->isFinished == true)
+
+	if (entry->isFinished)
 		return false;
 
 	/* Fill outerAddInfo */