From da361496110cb76432b00f5b469f8d37ebb6f15f Mon Sep 17 00:00:00 2001
From: santhreal <64453045+santhreal@users.noreply.github.com>
Date: Fri, 17 Jul 2026 23:55:55 -0700
Subject: [PATCH] fix: anchor newline-end strip to whole alternation

U_NL_END appended $ only to the last alternative, so Path.write_lines
stripped embedded newlines instead of trailing terminators only.
---
 path/__init__.py   | 7 +++++--
 tests/test_path.py | 7 +++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/path/__init__.py b/path/__init__.py
index 33dd979..683846b 100644
--- a/path/__init__.py
+++ b/path/__init__.py
@@ -98,8 +98,9 @@
 U_LINESEPS = LINESEPS + ['\u0085', '\u2028', '\u2029']
 B_NEWLINE = re.compile('|'.join(LINESEPS).encode())
 U_NEWLINE = re.compile('|'.join(U_LINESEPS))
-B_NL_END = re.compile(B_NEWLINE.pattern + b'$')
-U_NL_END = re.compile(U_NEWLINE.pattern + '$')
+# Group the alternation so $ anchors the whole newline, not only the last alt.
+B_NL_END = re.compile(b'(?:' + B_NEWLINE.pattern + b')$')
+U_NL_END = re.compile('(?:' + U_NEWLINE.pattern + ')$')
 
 _default_linesep = object()
 
@@ -155,6 +156,8 @@ def _strip_newlines(lines: Iterable[str]) -> Iterator[str]:
     r"""
     >>> list(_strip_newlines(['Hello World\r\n', 'foo']))
     ['Hello World', 'foo']
+    >>> list(_strip_newlines(['Hello\nWorld\n', 'foo']))
+    ['Hello\nWorld', 'foo']
     """
     return (U_NL_END.sub('', line) for line in lines)
 
diff --git a/tests/test_path.py b/tests/test_path.py
index b424bb6..1d74b22 100644
--- a/tests/test_path.py
+++ b/tests/test_path.py
@@ -318,6 +318,13 @@ def test_read_write(self, tmpdir):
         assert file.read_text(encoding='utf-8') == 'hello world'
         assert file.read_bytes() == b'hello world'
 
+    def test_write_lines_preserves_embedded_newlines(self, tmpdir):
+        file = path.Path(tmpdir) / 'filename'
+        file.write_lines(['Hello\nWorld', 'foo\r\nbar\n'], encoding='utf-8')
+        assert file.read_bytes() == (
+            f'Hello\nWorld{os.linesep}foo\r\nbar{os.linesep}'.encode()
+        )
+
 
 class TestPerformance:
     @staticmethod