From e9a05ed6fa1668e76699e360b300f828d52747dd Mon Sep 17 00:00:00 2001
From: Armin Ronacher <armin.ronacher@active-4.com>
Date: Fri, 29 Dec 2023 22:18:04 +0100
Subject: [PATCH] Fix overlap bug in LCS (#59)

* Fix overlap bug in LCS

* Mention pull request
---
 CHANGELOG.md          |  2 ++
 src/algorithms/lcs.rs | 30 +++++++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a0d9aff..b69881a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,8 @@ All notable changes to similar are documented here.
 ## 2.4.0
 
 * Fixed a bug where the LCS diff algorithm didn't always call `D::finish`.  (#58)
+* Fixed a bug in LCS that caused a panic if the common prefix and the
+  common suffix overlapped.  (#59)
 
 ## 2.3.0
 
diff --git a/src/algorithms/lcs.rs b/src/algorithms/lcs.rs
index ffead40..70c13d8 100644
--- a/src/algorithms/lcs.rs
+++ b/src/algorithms/lcs.rs
@@ -64,7 +64,12 @@ where
     }
 
     let common_prefix_len = common_prefix_len(old, old_range.clone(), new, new_range.clone());
-    let common_suffix_len = common_suffix_len(old, old_range.clone(), new, new_range.clone());
+    let common_suffix_len = common_suffix_len(
+        old,
+        old_range.start + common_prefix_len..old_range.end,
+        new,
+        new_range.start + common_prefix_len..new_range.end,
+    );
 
     // If the sequences are not different then we're done
     if common_prefix_len == old_range.len() && (old_range.len() == new_range.len()) {
@@ -266,3 +271,26 @@ fn test_finish_called() {
     diff(&mut d, slice, 0..slice.len(), slice, 0..slice.len()).unwrap();
     assert!(d.0);
 }
+
+#[test]
+fn test_bad_range_regression() {
+    use crate::algorithms::Capture;
+    use crate::DiffOp;
+    let mut d = Capture::new();
+    diff(&mut d, &[0], 0..1, &[0, 0], 0..2).unwrap();
+    assert_eq!(
+        d.into_ops(),
+        vec![
+            DiffOp::Equal {
+                old_index: 0,
+                new_index: 0,
+                len: 1
+            },
+            DiffOp::Insert {
+                old_index: 1,
+                new_index: 1,
+                new_len: 1
+            }
+        ]
+    );
+}