upgrade_pythoncapi: try to preserve newlines when patching

In case we use \n on Windows or \r\n on Linux we don't want
patching those files change every line due to newlines being
adjusted to the platform defaults.

Instead pass 'newline=""' to all open() calls to preserve
newlines. And when adding new lines use the first type of
newline found in the file.

The test changes make the patching code reuseable and adds
a second test with multiple different newlines in the input.

Author: lazka

tests/test_upgrade_pythoncapi.py

@@ -43,33 +43,12 @@ def reformat(source):
 class Tests(unittest.TestCase):
     maxDiff = 80 * 30
 
-    def _test_patch_file(self, tmp_dir):
-        # test Patcher.patcher()
-        source = """
-            PyTypeObject*
-            test_type(PyObject *obj, PyTypeObject *type)
-            {
-                Py_TYPE(obj) = type;
-                return Py_TYPE(obj);
-            }
-        """
-        expected = """
-            #include "pythoncapi_compat.h"
-
-            PyTypeObject*
-            test_type(PyObject *obj, PyTypeObject *type)
-            {
-                Py_SET_TYPE(obj, type);
-                return Py_TYPE(obj);
-            }
-        """
-        source = reformat(source)
-        expected = reformat(expected)
-
+    def _patch_file(self, source, tmp_dir=None):
+         # test Patcher.patcher()
         filename = tempfile.mktemp(suffix='.c', dir=tmp_dir)
         old_filename = filename + ".old"
         try:
-            with open(filename, "w", encoding="utf-8") as fp:
+            with open(filename, "w", encoding="utf-8", newline="") as fp:
                 fp.write(source)
 
             old_stderr = sys.stderr
@@ -93,10 +72,10 @@ def _test_patch_file(self, tmp_dir):
                 sys.stderr = old_stderr
                 sys.argv = old_argv
 
-            with open(filename, encoding="utf-8") as fp:
+            with open(filename, encoding="utf-8", newline="") as fp:
                 new_contents = fp.read()
 
-            with open(old_filename, encoding="utf-8") as fp:
+            with open(old_filename, encoding="utf-8", newline="") as fp:
                 old_contents = fp.read()
         finally:
             try:
@@ -108,15 +87,53 @@ def _test_patch_file(self, tmp_dir):
             except FileNotFoundError:
                 pass
 
-        self.assertEqual(new_contents, expected)
         self.assertEqual(old_contents, source)
+        return new_contents
 
     def test_patch_file(self):
-        self._test_patch_file(None)
+        source = """
+            PyTypeObject*
+            test_type(PyObject *obj, PyTypeObject *type)
+            {
+                Py_TYPE(obj) = type;
+                return Py_TYPE(obj);
+            }
+        """
+        expected = """
+            #include "pythoncapi_compat.h"
+
+            PyTypeObject*
+            test_type(PyObject *obj, PyTypeObject *type)
+            {
+                Py_SET_TYPE(obj, type);
+                return Py_TYPE(obj);
+            }
+        """
+        source = reformat(source)
+        expected = reformat(expected)
+
+        new_contents = self._patch_file(source)
+        self.assertEqual(new_contents, expected)
 
-    def test_patch_directory(self):
         with tempfile.TemporaryDirectory() as tmp_dir:
-            self._test_patch_file(tmp_dir)
+            new_contents = self._patch_file(source, tmp_dir)
+            self.assertEqual(new_contents, expected)
+
+    def test_patch_file_preserve_newlines(self):
+        source = """
+            Py_ssize_t get_size(PyVarObject *obj)\r\n\
+            \n\
+            { return obj->ob_size; }\r\
+        """
+        expected = """
+            Py_ssize_t get_size(PyVarObject *obj)\r\n\
+            \n\
+            { return Py_SIZE(obj); }\r\
+        """
+        source = reformat(source)
+        expected = reformat(expected)
+        new_contents = self._patch_file(source)
+        self.assertEqual(new_contents, expected)
 
     def check_replace(self, source, expected, **kwargs):
         source = reformat(source)

upgrade_pythoncapi.py

@@ -554,13 +554,17 @@ def _get_operations(self, parser):
         return operations
 
     def add_line(self, content, line):
-        line = line + '\n'
+        # Use the first matching newline
+        match = re.search(r'(?:\r\n|\n|\r)', content)
+        newline = match.group(0) if match else '\n'
+
+        line = line + newline
         # FIXME: tolerate trailing spaces
         if line not in content:
             # FIXME: add macro after the first header comment
             # FIXME: add macro after includes
             # FIXME: add macro after: #define PY_SSIZE_T_CLEAN
-            return line + '\n' + content
+            return line + newline + content
         else:
             return content
 
@@ -601,7 +605,7 @@ def patch_file(self, filename):
         encoding = "utf-8"
         errors = "surrogateescape"
 
-        with open(filename, encoding=encoding, errors=errors) as fp:
+        with open(filename, encoding=encoding, errors=errors, newline="") as fp:
             old_contents = fp.read()
 
         new_contents, operations = self._patch(old_contents)
@@ -620,7 +624,7 @@ def patch_file(self, filename):
             # If old_filename already exists, replace it
             os.replace(filename, old_filename)
 
-        with open(filename, "w", encoding=encoding, errors=errors) as fp:
+        with open(filename, "w", encoding=encoding, errors=errors, newline="") as fp:
             fp.write(new_contents)
 
         self.applied_operations |= set(operations)