[rollup] Preserve apply-patch existing-file newline style (fork #1 / upstream codex#4003)

codex-rs/apply-patch/src/lib.rs

@@ -664,7 +664,11 @@ async fn derive_new_contents_from_chunks(
         })
     })?;
 
-    let mut original_lines: Vec<String> = original_contents.split('\n').map(String::from).collect();
+    let line_separator = detect_line_separator(&original_contents);
+    let mut original_lines: Vec<String> = original_contents
+        .split('\n')
+        .map(|line| line.strip_suffix('\r').unwrap_or(line).to_string())
+        .collect();
 
     // Drop the trailing empty element that results from the final newline so
     // that line counts match the behaviour of standard `diff`.
@@ -678,13 +682,28 @@ async fn derive_new_contents_from_chunks(
     if !new_lines.last().is_some_and(String::is_empty) {
         new_lines.push(String::new());
     }
-    let new_contents = new_lines.join("\n");
+    let new_contents = new_lines.join(line_separator);
     Ok(AppliedPatch {
         original_contents,
         new_contents,
     })
 }
 
+fn detect_line_separator(contents: &str) -> &'static str {
+    let lf_count = contents
+        .as_bytes()
+        .iter()
+        .filter(|byte| **byte == b'\n')
+        .count();
+    let crlf_count = contents.match_indices("\r\n").count();
+
+    if lf_count > 0 && lf_count == crlf_count {
+        "\r\n"
+    } else {
+        "\n"
+    }
+}
+
 /// Compute a list of replacements needed to transform `original_lines` into the
 /// new lines, given the patch `chunks`. Each replacement is returned as
 /// `(start_index, old_len, new_lines)`.

codex-rs/apply-patch/tests/fixtures/scenarios/.gitattributes

@@ -1 +1,3 @@
 ** text eol=lf
+023_update_preserves_crlf/input/lines.txt text eol=crlf
+023_update_preserves_crlf/expected/lines.txt text eol=crlf

codex-rs/apply-patch/tests/fixtures/scenarios/023_update_preserves_crlf/expected/lines.txt

@@ -0,0 +1,3 @@
+alpha
+BETA
+gamma

codex-rs/apply-patch/tests/fixtures/scenarios/023_update_preserves_crlf/input/lines.txt

@@ -0,0 +1,3 @@
+alpha
+beta
+gamma

codex-rs/apply-patch/tests/fixtures/scenarios/023_update_preserves_crlf/patch.txt

@@ -0,0 +1,10 @@
+*** Begin Patch
+*** Update File: lines.txt
+@@
+-alpha
+-beta
+-gamma
++alpha
++BETA
++gamma
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/024_update_preserves_lf/expected/lines.txt

@@ -0,0 +1,3 @@
+alpha
+BETA
+gamma

codex-rs/apply-patch/tests/fixtures/scenarios/024_update_preserves_lf/input/lines.txt

@@ -0,0 +1,3 @@
+alpha
+beta
+gamma

codex-rs/apply-patch/tests/fixtures/scenarios/024_update_preserves_lf/patch.txt

@@ -0,0 +1,10 @@
+*** Begin Patch
+*** Update File: lines.txt
+@@
+-alpha
+-beta
+-gamma
++alpha
++BETA
++gamma
+*** End Patch