gh-139423: Fix plistlib to preserve carriage returns in XML plist round-trips

plistlib's _escape() function was normalizing \r\n to \n and \r to \n
during XML plist serialization. When the plist was loaded back, the
original carriage return characters were lost because expat also
normalizes newlines in XML character data.

Fix by encoding \r as the XML character reference 
 instead of
converting it to \n. Character references are not subject to XML
newline normalization, so expat correctly decodes 
 back to \r,
preserving the original data during round-trips.

Author: gaweng

Lib/plistlib.py

@@ -164,11 +164,10 @@ def _escape(text):
     if m is not None:
         raise ValueError("strings can't contain control characters; "
                          "use bytes instead")
-    text = text.replace("\r\n", "\n")       # convert DOS line endings
-    text = text.replace("\r", "\n")         # convert Mac line endings
     text = text.replace("&", "&")       # escape '&'
     text = text.replace("<", "&lt;")        # escape '<'
     text = text.replace(">", "&gt;")        # escape '>'
+    text = text.replace("\r", "&#13;")      # preserve CR via character reference
     return text
 
 class _PlistParser:

Lib/test/test_plistlib.py

@@ -818,13 +818,26 @@ def test_controlcharacters(self):
             if i >= 32 or c in "\r\n\t":
                 # \r, \n and \t are the only legal control chars in XML
                 data = plistlib.dumps(testString, fmt=plistlib.FMT_XML)
-                if c != "\r":
-                    self.assertEqual(plistlib.loads(data), testString)
+                self.assertEqual(plistlib.loads(data), testString)
             else:
                 with self.assertRaises(ValueError):
                     plistlib.dumps(testString, fmt=plistlib.FMT_XML)
             plistlib.dumps(testString, fmt=plistlib.FMT_BINARY)
 
+    def test_cr_newline_roundtrip(self):
+        # gh-139423: Carriage returns should survive XML plist round-trip.
+        test_cases = [
+            "hello\rworld",        # standalone CR
+            "hello\r\nworld",      # CRLF
+            "a\rb\nc\r\nd",        # mixed newlines
+            "\r",                   # bare CR
+            "\r\n",                 # bare CRLF
+        ]
+        for s in test_cases:
+            with self.subTest(s=s):
+                data = plistlib.dumps(s, fmt=plistlib.FMT_XML)
+                self.assertEqual(plistlib.loads(data), s)
+
     def test_non_bmp_characters(self):
         pl = {'python': '\U0001f40d'}
         for fmt in ALL_FORMATS:

Misc/NEWS.d/next/Library/2026-04-09-14-30-00.gh-issue-139423.UD0SN_qTKdI.rst

@@ -0,0 +1,4 @@
+Fixed :mod:`plistlib` to preserve carriage return characters (``\r``) during
+XML plist round-trips. Previously, ``\r`` and ``\r\n`` were normalized to
+``\n`` during serialization, causing data corruption. Carriage returns are now
+encoded as ``
`` XML character references, which the XML parser preserves.