From 4328338e98100ecd69ac22460c310c0837535cf8 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 25 May 2023 23:39:12 +0100
Subject: [PATCH 1/2] GH-103631: Fix `PurePosixPath(PureWindowsPath(...))`
 separator handling

For backwards compatibility, accept backslashes as path separators in
`PurePosixPath` if an instance of `PureWindowsPath` is supplied.
---
 Lib/pathlib.py                                              | 3 +++
 Lib/test/test_pathlib.py                                    | 6 ++++++
 .../Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst  | 2 ++
 3 files changed, 11 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index fb78939dcc31ba..789402116be518 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -300,6 +300,9 @@ def __init__(self, *args):
         for arg in args:
             if isinstance(arg, PurePath):
                 path = arg._raw_path
+                if arg._flavour is ntpath and self._flavour is posixpath:
+                    # GH-103631: Convert separators for backwards compatibility.
+                    path = path.replace('\\', '/')
             else:
                 try:
                     path = os.fspath(arg)
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index 8b68cdc9b7d003..16f01445b7f48e 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -789,6 +789,12 @@ def test_div(self):
         pp = P('//a') / '/c'
         self.assertEqual(pp, P('/c'))
 
+    def test_parse_windows_path(self):
+        P = self.cls
+        p = P('c:', 'a', 'b')
+        pp = P(pathlib.PureWindowsPath('c:\\a\\b'))
+        self.assertEqual(p, pp)
+
 
 class PureWindowsPathTest(_BasePurePathTest, unittest.TestCase):
     cls = pathlib.PureWindowsPath
diff --git a/Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst b/Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst
new file mode 100644
index 00000000000000..036ed54bc3e451
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst
@@ -0,0 +1,2 @@
+Fix ``pathlib.PurePosixPath(pathlib.PureWindowsPath(...))`` not converting
+path separators.

From 6a612f4187620358fef9f6c99f0017a1c9dcbe2a Mon Sep 17 00:00:00 2001
From: "Gregory P. Smith" <greg@krypto.org>
Date: Fri, 26 May 2023 10:38:35 -0700
Subject: [PATCH 2/2] mention this matches 3.11 in the news entry

---
 .../next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst b/Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst
index 036ed54bc3e451..d1eb2d3ed6191f 100644
--- a/Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst
+++ b/Misc/NEWS.d/next/Library/2023-05-25-23-34-54.gh-issue-103631.x5Urye.rst
@@ -1,2 +1,2 @@
 Fix ``pathlib.PurePosixPath(pathlib.PureWindowsPath(...))`` not converting
-path separators.
+path separators to restore 3.11 compatible behavior.