From fab3e245ff7c0b43d0b3ec0e61f9ce0270ced72f Mon Sep 17 00:00:00 2001
From: Charlie Marsh <charliemarsh@openai.com>
Date: Thu, 2 Jul 2026 15:48:25 -0400
Subject: [PATCH] Support CR line endings in apply_patch

---
 codex-rs/apply-patch/src/text_file.rs    | 25 ++++++++++++++++--------
 codex-rs/apply-patch/tests/suite/tool.rs | 16 +++++++++++++--
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/codex-rs/apply-patch/src/text_file.rs b/codex-rs/apply-patch/src/text_file.rs
index da5fa237f3..b7d598ca97 100644
--- a/codex-rs/apply-patch/src/text_file.rs
+++ b/codex-rs/apply-patch/src/text_file.rs
@@ -4,6 +4,7 @@ pub(super) type Replacement = (usize, usize, Vec<String>);
 enum LineEnding {
     Lf,
     CrLf,
+    Cr,
 }
 
 impl LineEnding {
@@ -11,6 +12,7 @@ impl LineEnding {
         match self {
             Self::Lf => "\n",
             Self::CrLf => "\r\n",
+            Self::Cr => "\r",
         }
     }
 }
@@ -34,20 +36,27 @@ impl SourceFile {
         let mut lines = Vec::new();
         let mut preferred_ending = None;
         let mut line_start = 0;
+        let mut cursor = 0;
 
-        for (newline, _) in contents.match_indices('\n') {
-            let line = &contents[line_start..newline];
-            let (text, ending) = if let Some(text) = line.strip_suffix('\r') {
-                (text, LineEnding::CrLf)
-            } else {
-                (line, LineEnding::Lf)
+        while cursor < contents.len() {
+            let (ending, ending_len) = match contents.as_bytes()[cursor] {
+                b'\r' if contents.as_bytes().get(cursor + 1) == Some(&b'\n') => {
+                    (LineEnding::CrLf, 2)
+                }
+                b'\r' => (LineEnding::Cr, 1),
+                b'\n' => (LineEnding::Lf, 1),
+                _ => {
+                    cursor += 1;
+                    continue;
+                }
             };
             preferred_ending.get_or_insert(ending);
             lines.push(SourceLine {
-                text: text.to_string(),
+                text: contents[line_start..cursor].to_string(),
                 ending: Some(ending),
             });
-            line_start = newline + 1;
+            cursor += ending_len;
+            line_start = cursor;
         }
 
         if line_start < contents.len() {
diff --git a/codex-rs/apply-patch/tests/suite/tool.rs b/codex-rs/apply-patch/tests/suite/tool.rs
index 3a50bdefad..9ec880931d 100644
--- a/codex-rs/apply-patch/tests/suite/tool.rs
+++ b/codex-rs/apply-patch/tests/suite/tool.rs
@@ -96,6 +96,18 @@ fn test_apply_patch_cli_preserves_crlf_from_target_file() -> anyhow::Result<()>
     )
 }
 
+#[test]
+fn test_apply_patch_cli_preserves_cr_from_target_file() -> anyhow::Result<()> {
+    let patch = "*** Begin Patch\n*** Update File: cr.txt\n@@\n-one\n+uno\n@@\n two\n+\n+between\n three\n*** End Patch";
+
+    assert_apply_patch_updates_file(
+        "cr.txt",
+        b"one\rtwo\rthree\r",
+        patch,
+        b"uno\rtwo\r\rbetween\rthree\r",
+    )
+}
+
 #[test]
 fn test_apply_patch_cli_preserves_change_order_with_repeated_lines() -> anyhow::Result<()> {
     let patch =
@@ -118,9 +130,9 @@ fn test_apply_patch_cli_preserves_untouched_mixed_line_endings() -> anyhow::Resu
 
     assert_apply_patch_updates_file(
         "mixed.txt",
-        b"one\r\ntwo\nthree\r\nfour\n",
+        b"one\r\ntwo\rthree\nfour\r\n",
         patch,
-        b"one\r\ntwo\nTHREE\r\nfour\n",
+        b"one\r\ntwo\rTHREE\r\nfour\r\n",
     )
 }