bpo-34108: Fix double carriage return in 2to3 on Windows (GH-8271) (#8275)

* Add test capturing failure. * Honor newlines as present in the original file. (cherry picked from commit cafaf04) Co-authored-by: Jason R. Coombs <jaraco@jaraco.com>

Author: miss-islington

Lib/lib2to3/refactor.py

@@ -514,7 +514,7 @@ def write_file(self, new_text, filename, old_text, encoding=None):
  set.
  """
  try:
- fp = io.open(filename, "w", encoding=encoding)
+ fp = io.open(filename, "w", encoding=encoding, newline='')
  except OSError as err:
  self.log_error("Can't create %s: %s", filename, err)
  return

Lib/lib2to3/tests/test_refactor.py

@@ -300,6 +300,7 @@ def test_crlf_unchanged(self):
  old, new = self.refactor_file(fn)
  self.assertIn(b"\r\n", old)
  self.assertIn(b"\r\n", new)
+ self.assertNotIn(b"\r\r\n", new)
 
  def test_refactor_docstring(self):
  rt = self.rt()

Misc/NEWS.d/next/Library/2018-07-13-08-44-52.bpo-34108.RjobUC.rst

@@ -0,0 +1 @@
+Remove extraneous CR in 2to3 refactor.