From b5f7777cb3ecae02d49e0b348968c1ff1ffe21f4 Mon Sep 17 00:00:00 2001
From: Barney Gale <barney.gale@gmail.com>
Date: Wed, 11 Oct 2023 04:45:11 +0100
Subject: [PATCH] GH-110488: Fix two small issues in
 `pathlib.PurePath.with_name()` (#110651)

Ensure that `PurePath('foo/a').with_name('.')` raises `ValueError`

Ensure that `PureWindowsPath('foo/a').with_name('a:b')` does not raise
`ValueError`.
---
 Lib/pathlib.py                                     |  3 +--
 Lib/test/test_pathlib.py                           | 14 ++++++++++----
 .../2023-10-10-22-54-56.gh-issue-110488.2I7OiZ.rst |  4 ++++
 3 files changed, 15 insertions(+), 6 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2023-10-10-22-54-56.gh-issue-110488.2I7OiZ.rst

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index 9e6d0754eccf3e..5c1c71ecec2805 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -603,8 +603,7 @@ def with_name(self, name):
         if not self.name:
             raise ValueError("%r has an empty name" % (self,))
         m = self.pathmod
-        drv, root, tail = m.splitroot(name)
-        if drv or root or not tail or m.sep in tail or (m.altsep and m.altsep in tail):
+        if not name or m.sep in name or (m.altsep and m.altsep in name) or name == '.':
             raise ValueError("Invalid name %r" % (name))
         return self._from_parsed_parts(self.drive, self.root,
                                        self._tail[:-1] + [name])
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index f077825fc7c09a..2781e019220353 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -614,6 +614,7 @@ def test_with_name_common(self):
         self.assertRaises(ValueError, P('.').with_name, 'd.xml')
         self.assertRaises(ValueError, P('/').with_name, 'd.xml')
         self.assertRaises(ValueError, P('a/b').with_name, '')
+        self.assertRaises(ValueError, P('a/b').with_name, '.')
         self.assertRaises(ValueError, P('a/b').with_name, '/c')
         self.assertRaises(ValueError, P('a/b').with_name, 'c/')
         self.assertRaises(ValueError, P('a/b').with_name, 'c/d')
@@ -631,6 +632,7 @@ def test_with_stem_common(self):
         self.assertRaises(ValueError, P('.').with_stem, 'd')
         self.assertRaises(ValueError, P('/').with_stem, 'd')
         self.assertRaises(ValueError, P('a/b').with_stem, '')
+        self.assertRaises(ValueError, P('a/b').with_stem, '.')
         self.assertRaises(ValueError, P('a/b').with_stem, '/c')
         self.assertRaises(ValueError, P('a/b').with_stem, 'c/')
         self.assertRaises(ValueError, P('a/b').with_stem, 'c/d')
@@ -1235,8 +1237,10 @@ def test_with_name(self):
         self.assertRaises(ValueError, P('c:').with_name, 'd.xml')
         self.assertRaises(ValueError, P('c:/').with_name, 'd.xml')
         self.assertRaises(ValueError, P('//My/Share').with_name, 'd.xml')
-        self.assertRaises(ValueError, P('c:a/b').with_name, 'd:')
-        self.assertRaises(ValueError, P('c:a/b').with_name, 'd:e')
+        self.assertEqual(str(P('a').with_name('d:')), '.\\d:')
+        self.assertEqual(str(P('a').with_name('d:e')), '.\\d:e')
+        self.assertEqual(P('c:a/b').with_name('d:'), P('c:a/d:'))
+        self.assertEqual(P('c:a/b').with_name('d:e'), P('c:a/d:e'))
         self.assertRaises(ValueError, P('c:a/b').with_name, 'd:/e')
         self.assertRaises(ValueError, P('c:a/b').with_name, '//My/Share')
 
@@ -1249,8 +1253,10 @@ def test_with_stem(self):
         self.assertRaises(ValueError, P('c:').with_stem, 'd')
         self.assertRaises(ValueError, P('c:/').with_stem, 'd')
         self.assertRaises(ValueError, P('//My/Share').with_stem, 'd')
-        self.assertRaises(ValueError, P('c:a/b').with_stem, 'd:')
-        self.assertRaises(ValueError, P('c:a/b').with_stem, 'd:e')
+        self.assertEqual(str(P('a').with_stem('d:')), '.\\d:')
+        self.assertEqual(str(P('a').with_stem('d:e')), '.\\d:e')
+        self.assertEqual(P('c:a/b').with_stem('d:'), P('c:a/d:'))
+        self.assertEqual(P('c:a/b').with_stem('d:e'), P('c:a/d:e'))
         self.assertRaises(ValueError, P('c:a/b').with_stem, 'd:/e')
         self.assertRaises(ValueError, P('c:a/b').with_stem, '//My/Share')
 
diff --git a/Misc/NEWS.d/next/Library/2023-10-10-22-54-56.gh-issue-110488.2I7OiZ.rst b/Misc/NEWS.d/next/Library/2023-10-10-22-54-56.gh-issue-110488.2I7OiZ.rst
new file mode 100644
index 00000000000000..aec9120d72e358
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-10-10-22-54-56.gh-issue-110488.2I7OiZ.rst
@@ -0,0 +1,4 @@
+Fix a couple of issues in :meth:`pathlib.PurePath.with_name`: a single dot
+was incorrectly considered a valid name, and in :class:`PureWindowsPath`, a
+name with an NTFS alternate data stream, like ``a:b``, was incorrectly
+considered invalid.