bpo-11594: Ensure line-endings are respected when using 2to3 (GH-6483)

(cherry picked from commit c127a86e1862df88ec6f9d15b79c627fc616766e)

Co-authored-by: Aaron Ang <aaronang@users.noreply.github.com>

3 files changed, 34 insertions, 18 deletions

diff --git a/Lib/lib2to3/refactor.py b/Lib/lib2to3/refactor.py
index db2e38d22f..7c4e064997 100644
--- a/Lib/lib2to3/refactor.py
+++ b/Lib/lib2to3/refactor.py
@@ -314,7 +314,7 @@ class RefactoringTool(object):
             encoding = tokenize.detect_encoding(f.readline)[0]
         finally:
             f.close()
-        with io.open(filename, "r", encoding=encoding) as f:
+        with io.open(filename, "r", encoding=encoding, newline='') as f:
             return f.read(), encoding
 
     def refactor_file(self, filename, write=False, doctests_only=False):
diff --git a/Lib/lib2to3/tests/data/crlf.py b/Lib/lib2to3/tests/data/crlf.py
index dbe2d7bb10..a83ca8f0a2 100644
--- a/Lib/lib2to3/tests/data/crlf.py
+++ b/Lib/lib2to3/tests/data/crlf.py
@@ -1,3 +1,3 @@
-print "hi"
-
-print "Like bad Windows newlines?"
+print "hi"

+

+print "Like bad Windows newlines?"

diff --git a/Lib/lib2to3/tests/test_refactor.py b/Lib/lib2to3/tests/test_refactor.py
index e9bae5e45d..f3059a9311 100644
--- a/Lib/lib2to3/tests/test_refactor.py
+++ b/Lib/lib2to3/tests/test_refactor.py
@@ -180,32 +180,42 @@ from __future__ import print_function"""
     def check_file_refactoring(self, test_file, fixers=_2TO3_FIXERS,
                                options=None, mock_log_debug=None,
                                actually_write=True):
-        tmpdir = tempfile.mkdtemp(prefix="2to3-test_refactor")
-        self.addCleanup(shutil.rmtree, tmpdir)
-        # make a copy of the tested file that we can write to
-        shutil.copy(test_file, tmpdir)
-        test_file = os.path.join(tmpdir, os.path.basename(test_file))
-        os.chmod(test_file, 0o644)
-
-        def read_file():
-            with open(test_file, "rb") as fp:
-                return fp.read()
-
-        old_contents = read_file()
+        test_file = self.init_test_file(test_file)
+        old_contents = self.read_file(test_file)
         rt = self.rt(fixers=fixers, options=options)
         if mock_log_debug:
             rt.log_debug = mock_log_debug
 
         rt.refactor_file(test_file)
-        self.assertEqual(old_contents, read_file())
+        self.assertEqual(old_contents, self.read_file(test_file))
 
         if not actually_write:
             return
         rt.refactor_file(test_file, True)
-        new_contents = read_file()
+        new_contents = self.read_file(test_file)
         self.assertNotEqual(old_contents, new_contents)
         return new_contents
 
+    def init_test_file(self, test_file):
+        tmpdir = tempfile.mkdtemp(prefix="2to3-test_refactor")
+        self.addCleanup(shutil.rmtree, tmpdir)
+        shutil.copy(test_file, tmpdir)
+        test_file = os.path.join(tmpdir, os.path.basename(test_file))
+        os.chmod(test_file, 0o644)
+        return test_file
+
+    def read_file(self, test_file):
+        with open(test_file, "rb") as fp:
+            return fp.read()
+
+    def refactor_file(self, test_file, fixers=_2TO3_FIXERS):
+        test_file = self.init_test_file(test_file)
+        old_contents = self.read_file(test_file)
+        rt = self.rt(fixers=fixers)
+        rt.refactor_file(test_file, True)
+        new_contents = self.read_file(test_file)
+        return old_contents, new_contents
+
     def test_refactor_file(self):
         test_file = os.path.join(FIXER_DIR, "parrot_example.py")
         self.check_file_refactoring(test_file, _DEFAULT_FIXERS)
@@ -285,6 +295,12 @@ from __future__ import print_function"""
         finally:
             os.linesep = old_sep
 
+    def test_crlf_unchanged(self):
+        fn = os.path.join(TEST_DATA_DIR, "crlf.py")
+        old, new = self.refactor_file(fn)
+        self.assertIn(b"\r\n", old)
+        self.assertIn(b"\r\n", new)
+
     def test_refactor_docstring(self):
         rt = self.rt()