From 242f91c73e0c57aace65a214477224edd6eac43e Mon Sep 17 00:00:00 2001
From: Ralf Lang <ralf.lang@ralf-lang.de>
Date: Fri, 13 Nov 2026 11:07:37 +0100
Subject: [PATCH 1/2] test(native): Cover native engine lcpos behaviour.

This is a followup to #8 by @bearoff.
---
 test/EngineTest.php              | 20 ++++++++++++++++++++
 test/Unnamespaced/EngineTest.php | 17 +++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/test/EngineTest.php b/test/EngineTest.php
index 30a8c1f..32dbd82 100644
--- a/test/EngineTest.php
+++ b/test/EngineTest.php
@@ -10,8 +10,10 @@
 
 namespace Horde\Text\Diff\Test;
 
+use Horde\Text\Diff\AddOperation;
 use Horde\Text\Diff\ChangeOperation;
 use Horde\Text\Diff\CopyOperation;
+use Horde\Text\Diff\DeleteOperation;
 use Horde\Text\Diff\Diff;
 use Horde\Text\Diff\Exception;
 use Horde\Text\Diff\NativeEngine;
@@ -61,6 +63,24 @@ public function testNativeEngine()
         $this->_testDiff($diff);
     }
 
+    public function testNativeEngineWithRepeatedLines()
+    {
+        $diff = Diff::fromFileLineArrays(
+            ['B', 'C', 'C', 'C', 'C', 'D'],
+            ['C', 'D', 'C', 'D', 'B', 'C'],
+            NativeEngine::class
+        );
+        $edits = $diff->getDiff()->toArray();
+
+        $this->assertCount(3, $edits);
+        $this->assertInstanceOf(DeleteOperation::class, $edits[0]);
+        $this->assertSame(['B', 'C', 'C', 'C'], $edits[0]->orig);
+        $this->assertInstanceOf(CopyOperation::class, $edits[1]);
+        $this->assertSame(['C', 'D'], $edits[1]->orig);
+        $this->assertInstanceOf(AddOperation::class, $edits[2]);
+        $this->assertSame(['C', 'D', 'B', 'C'], $edits[2]->final);
+    }
+
     public function testShellEngine()
     {
         if (!exec('which diff')) {
diff --git a/test/Unnamespaced/EngineTest.php b/test/Unnamespaced/EngineTest.php
index 8c772b3..ffec389 100644
--- a/test/Unnamespaced/EngineTest.php
+++ b/test/Unnamespaced/EngineTest.php
@@ -51,6 +51,23 @@ public function testNativeEngine()
         $this->_testDiff($diff);
     }
 
+    public function testNativeEngineWithRepeatedLines()
+    {
+        $diff = new Horde_Text_Diff('Native', [
+            ['B', 'C', 'C', 'C', 'C', 'D'],
+            ['C', 'D', 'C', 'D', 'B', 'C'],
+        ]);
+        $edits = $diff->getDiff();
+
+        $this->assertCount(3, $edits);
+        $this->assertInstanceOf('Horde_Text_Diff_Op_Delete', $edits[0]);
+        $this->assertSame(['B', 'C', 'C', 'C'], $edits[0]->orig);
+        $this->assertInstanceOf('Horde_Text_Diff_Op_Copy', $edits[1]);
+        $this->assertSame(['C', 'D'], $edits[1]->orig);
+        $this->assertInstanceOf('Horde_Text_Diff_Op_Add', $edits[2]);
+        $this->assertSame(['C', 'D', 'B', 'C'], $edits[2]->final);
+    }
+
     public function testShellEngine()
     {
         if (!exec('which diff')) {

From bf0977706aafb40a18769d7a897da44728736094 Mon Sep 17 00:00:00 2001
From: Ralf Lang <ralf.lang@ralf-lang.de>
Date: Fri, 13 Nov 2026 11:32:07 +0100
Subject: [PATCH 2/2] fix(NativeEngine): Formally define $k at a higher level
 before it is used by independent sibling levels

---
 .horde.yml           |  4 +++-
 src/NativeEngine.php | 11 +++++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/.horde.yml b/.horde.yml
index 83ff42d..067d0c8 100644
--- a/.horde.yml
+++ b/.horde.yml
@@ -44,7 +44,9 @@ dependencies:
       horde/cli: ^3
       horde/test: ^3
 vendor: horde
-keywords: null
+keywords:
+  - diff
+  - patch
 ci-platform:
   '8.1':
     - php: ^7.4 || ^8
diff --git a/src/NativeEngine.php b/src/NativeEngine.php
index f4b6af9..b6d57ac 100644
--- a/src/NativeEngine.php
+++ b/src/NativeEngine.php
@@ -106,9 +106,10 @@ public function diff(): OperationList
         $this->xchanged = $this->ychanged = [];
         $this->xv = $this->yv = [];
         $this->xind = $this->yind = [];
-        unset($this->seq);
-        unset($this->in_seq);
-        unset($this->lcs);
+        // In modern PHP we cannot unset as NativeEngine may be subclassed and subclasses may have hooks
+        $this->seq = null;
+        $this->in_seq = null;
+        $this->lcs = null;
 
         // Skip leading common lines.
         for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
@@ -243,6 +244,8 @@ protected function _diag($xoff, $xlim, $yoff, $ylim, $nchunks)
 
         $numer = $xlim - $xoff + $nchunks - 1;
         $x = $xoff;
+        // $k should be defined by the first iteration reaching an empty inseq(y)
+        $k = null;
         for ($chunk = 0; $chunk < $nchunks; $chunk++) {
             if ($chunk > 0) {
                 for ($i = 0; $i <= $this->lcs; $i++) {
@@ -263,7 +266,7 @@ protected function _diag($xoff, $xlim, $yoff, $ylim, $nchunks)
                         assert($k > 0);
                         $ymids[$k] = $ymids[$k - 1];
                         break;
-                    } elseif ($y > $this->seq[$k - 1]) {
+                    } elseif (is_int($k) && ($k > 0) && ($y > $this->seq[$k - 1])) {
                         /*
                          * Disable this assertion for now until we know why it
                          * causes https://github.com/maintaina-com/Text_Diff/issues/12