fix: keep lock file eol

src/poetry/packages/locker.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import contextlib
 import json
 import logging
 import os
@@ -26,6 +27,7 @@
 from tomlkit import table
 
 from poetry.__version__ import __version__
+from poetry.toml import TOMLError
 from poetry.toml.file import TOMLFile
 from poetry.utils._compat import tomllib
 
@@ -291,6 +293,10 @@ def _should_write(self, lock: TOMLDocument) -> bool:
 
     def _write_lock_data(self, data: TOMLDocument) -> None:
         lockfile = TOMLFile(self.lock)
+        if self.lock.exists():
+            # get original line ending.
+            with contextlib.suppress(TOMLError):
+                lockfile.read()
         lockfile.write(data)
 
         self._lock_data = None

tests/packages/test_locker.py

@@ -1231,3 +1231,20 @@ def test_lockfile_is_not_rewritten_if_only_poetry_version_changed(
         content = f.read()
 
     assert content == old_content
+
+
+def test_lockfile_keep_eol(locker: Locker, root: ProjectPackage) -> None:
+    sep = "\n" if os.sep == "\r\n" else "\r\n"
+
+    with open(locker.lock, "wb") as f:
+        f.write((sep * 10).encode())
+
+    assert locker.set_lock_data(root, [Package("test", version="0.0.1")])
+
+    with locker.lock.open(encoding="utf-8", newline="") as f:
+        line, *_ = f.read().splitlines(keepends=True)
+
+    if sep == "\r\n":
+        assert line.endswith("\r\n")
+    else:
+        assert not line.endswith("\r\n")