Keep the file's newline style when refactoring

tokenize.open translates newlines while reading and write_text wrote \n, so
refactoring a CRLF file rewrote every line to LF. read() now also returns the
newline it saw, and the file is written back with it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019P9bvuGwAyVCNUdsAYPB1V

Author: claude

src/unexport/session.py

@@ -20,7 +20,7 @@ def get_source(self, path: Path) -> Iterator[tuple[str | None, Path, str | None]
         """Yield (source, path, error) for each file; source is None when the file can't be read."""
         for py_path in utils.list_paths(path, include=self.config.include, exclude=self.config.exclude):
             try:
-                source, _ = utils.read(py_path)
+                source, _, _ = utils.read(py_path)
             except utils.READ_ERRORS as exc:
                 yield None, py_path, str(exc)
             else:
@@ -36,9 +36,10 @@ def get_expected_all(source: str) -> tuple[bool, list[str]]:
 
     @classmethod
     def refactor(cls, path: Path, apply: bool = False) -> str:
-        source, encoding = utils.read(path)
+        source, encoding, newline = utils.read(path)
         _, expected_all = cls.get_expected_all(source)
         new_source = refactor_source(source, expected_all)
         if apply and new_source != source:
-            path.write_text(new_source, encoding=encoding)
+            with path.open("w", encoding=encoding, newline=newline) as file:
+                file.write(new_source)
         return new_source

src/unexport/utils.py

@@ -15,11 +15,14 @@
 READ_ERRORS = (OSError, SyntaxError, UnicodeDecodeError)
 
 
-def read(path: Path) -> tuple[str, str]:
+def read(path: Path) -> tuple[str, str, str]:
+    """Return (source with ``\\n`` newlines, encoding, the file's newline) so the file can be written back as it was."""
     with tokenize.open(path) as stream:
         source = stream.read()
         encoding = stream.encoding
-    return source, encoding
+        newlines = stream.newlines  # the newline(s) seen while reading: None, a str or a tuple of them
+    newline = newlines if isinstance(newlines, str) else (newlines or ("\n",))[0]
+    return source, encoding, newline
 
 
 def list_paths(

tests/test_main.py

@@ -5,7 +5,12 @@
 from unexport import utils
 from unexport.main import main
 
-__all__ = ["test_errors_are_reported", "test_read_errors", "test_several_statements_are_not_refactored"]
+__all__ = [
+    "test_errors_are_reported",
+    "test_read_errors",
+    "test_refactor_keeps_crlf_newlines",
+    "test_several_statements_are_not_refactored",
+]
 
 
 def test_errors_are_reported(tmp_path: Path, capsys):
@@ -54,3 +59,12 @@ def test_several_statements_are_not_refactored(tmp_path: Path, capsys):
     assert "Refactoring" not in output
     assert path.read_text() == source
     assert exit_code == 1
+
+
+def test_refactor_keeps_crlf_newlines(tmp_path: Path):
+    path = tmp_path / "crlf.py"
+    path.write_bytes(b"import os\r\n\r\nclass Public: ...\r\n")
+
+    main(["--refactor", path.as_posix()])
+
+    assert path.read_bytes() == b'import os\r\n\r\n__all__ = ["Public"]\r\n\r\nclass Public: ...\r\n'