From a7a8659383760ab76bc7c6f4a31c9e8fa1dafde5 Mon Sep 17 00:00:00 2001
From: Jochen Hunz <j.hunz@anchorpoint.app>
Date: Sat, 18 Jul 2026 12:43:09 +0200
Subject: [PATCH] fix(merge): keep conflict markers on their own lines

A conflicting hunk at end-of-file without a trailing newline glued the
next marker onto its last content line, producing unparseable output.
Matches git merge-file --diff3 behavior.

Signed-off-by: Jochen Hunz <j.hunz@anchorpoint.app>
---
 src/merge/mod.rs   |  6 ++++++
 src/merge/tests.rs | 26 ++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/src/merge/mod.rs b/src/merge/mod.rs
index 21f9197..320d834 100644
--- a/src/merge/mod.rs
+++ b/src/merge/mod.rs
@@ -604,6 +604,9 @@ fn add_conflict_marker(
     marker_len: usize,
     filename: Option<&str>,
 ) {
+    if !output.is_empty() && !output.ends_with('\n') {
+        output.push('\n');
+    }
     for _ in 0..marker_len {
         output.push(marker);
     }
@@ -684,6 +687,9 @@ fn add_conflict_marker_bytes(
     marker_len: usize,
     filename: Option<&[u8]>,
 ) {
+    if !output.is_empty() && output.last() != Some(&b'\n') {
+        output.push(b'\n');
+    }
     for _ in 0..marker_len {
         output.push(marker);
     }
diff --git a/src/merge/tests.rs b/src/merge/tests.rs
index 99188df..7a3a8c6 100644
--- a/src/merge/tests.rs
+++ b/src/merge/tests.rs
@@ -404,3 +404,29 @@ fn delete_and_insert_conflict() {
         "MergeRange (Theirs::delete, Ours::insert) conflict"
     );
 }
+
+#[test]
+fn conflict_hunks_without_trailing_newline_keep_markers_on_own_lines() {
+    let base = "This is line 1.\nThis is line 2.";
+    let ours = "This is line 1.\nThis is line 2 changed.";
+    let theirs = "This is line 1.\nThis is line 2 also changed.";
+
+    let expected = "\
+This is line 1.
+<<<<<<< ours
+This is line 2 changed.
+||||||| original
+This is line 2.
+=======
+This is line 2 also changed.
+>>>>>>> theirs
+";
+
+    assert_merge!(
+        base,
+        ours,
+        theirs,
+        Err(expected),
+        "file-final hunks without trailing newline",
+    );
+}