From d919179ba3a407aa58018c31df88f883eab0fea1 Mon Sep 17 00:00:00 2001
From: Viktor Lofgren <vlofgren@marginalia.nu>
Date: Mon, 25 Nov 2024 13:23:26 +0100
Subject: [PATCH] (index) Correct off-by-1 error in DocumentSpan.containsRange

---
 .../nu/marginalia/index/forward/spans/DocumentSpan.java   | 4 +++-
 .../index/forward/ForwardIndexSpansReaderTest.java        | 8 +++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/code/index/index-forward/java/nu/marginalia/index/forward/spans/DocumentSpan.java b/code/index/index-forward/java/nu/marginalia/index/forward/spans/DocumentSpan.java
index f1b32135..56b4e079 100644
--- a/code/index/index-forward/java/nu/marginalia/index/forward/spans/DocumentSpan.java
+++ b/code/index/index-forward/java/nu/marginalia/index/forward/spans/DocumentSpan.java
@@ -107,7 +107,7 @@ public class DocumentSpan {
                 continue;
             }
 
-            if (position + len < end) {
+            if (position + len <= end) {
                 return true;
             } else if (sei + 2 < startsEnds.size()) {
                 start = startsEnds.getInt(sei++);
@@ -198,6 +198,8 @@ public class DocumentSpan {
         var iter = startsEnds.iterator();
 
         while (iter.hasNext()) {
+            // The length of each span is b - a; but we receive them in the order a b;
+            // thus we subtract the start from the length and add the end
             len -= iter.nextInt();
             len += iter.nextInt();
         }
diff --git a/code/index/index-forward/test/nu/marginalia/index/forward/ForwardIndexSpansReaderTest.java b/code/index/index-forward/test/nu/marginalia/index/forward/ForwardIndexSpansReaderTest.java
index b668d1c7..f92ef785 100644
--- a/code/index/index-forward/test/nu/marginalia/index/forward/ForwardIndexSpansReaderTest.java
+++ b/code/index/index-forward/test/nu/marginalia/index/forward/ForwardIndexSpansReaderTest.java
@@ -1,5 +1,6 @@
 package nu.marginalia.index.forward;
 
+import it.unimi.dsi.fastutil.ints.IntList;
 import nu.marginalia.index.forward.spans.ForwardIndexSpansReader;
 import nu.marginalia.index.forward.spans.ForwardIndexSpansWriter;
 import nu.marginalia.language.sentence.tag.HtmlTag;
@@ -37,9 +38,10 @@ class ForwardIndexSpansReaderTest {
             writer.writeSpan(HtmlTag.HEADING.code, VarintCodedSequence.generate(1, 3, 5, 8).buffer());
             offset1 = writer.endRecord();
 
-            writer.beginRecord(2);
+            writer.beginRecord(3);
             writer.writeSpan(HtmlTag.CODE.code, VarintCodedSequence.generate(2, 4, 6, 7).buffer());
             writer.writeSpan(HtmlTag.ANCHOR.code, VarintCodedSequence.generate(3, 5).buffer());
+            writer.writeSpan(HtmlTag.NAV.code, VarintCodedSequence.generate(1, 3).buffer());
             offset2 = writer.endRecord();
         }
 
@@ -60,6 +62,10 @@ class ForwardIndexSpansReaderTest {
             assertFalse(spans2.code.containsPosition(7));
             assertFalse(spans2.code.containsPosition(8));
 
+            assertTrue(spans2.nav.containsRange(IntList.of(1), 2));
+            assertTrue(spans2.nav.containsRange(IntList.of(2), 1));
+            assertTrue(spans2.nav.containsPosition(1));
+
             assertEquals(1, spans2.anchor.size());
 
             assertEquals(0, spans2.title.size());