[utils] `sanitize_path`: Fix some incorrect behavior (#11923)

Authored by: Grub4K

2 files changed, 34 insertions, 12 deletions

diff --git a/test/test_utils.py b/test/test_utils.py
index b3de14198..8f81d0b1b 100644
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -249,17 +249,36 @@ class TestUtil(unittest.TestCase):
         self.assertEqual(sanitize_path('abc/def...'), 'abc\\def..#')
         self.assertEqual(sanitize_path('abc.../def'), 'abc..#\\def')
         self.assertEqual(sanitize_path('abc.../def...'), 'abc..#\\def..#')
-
-        self.assertEqual(sanitize_path('../abc'), '..\\abc')
-        self.assertEqual(sanitize_path('../../abc'), '..\\..\\abc')
-        self.assertEqual(sanitize_path('./abc'), 'abc')
-        self.assertEqual(sanitize_path('./../abc'), '..\\abc')
-
-        self.assertEqual(sanitize_path('\\abc'), '\\abc')
-        self.assertEqual(sanitize_path('C:abc'), 'C:abc')
-        self.assertEqual(sanitize_path('C:abc\\..\\'), 'C:..')
         self.assertEqual(sanitize_path('C:\\abc:%(title)s.%(ext)s'), 'C:\\abc#%(title)s.%(ext)s')
 
+        # Check with nt._path_normpath if available
+        try:
+            import nt
+
+            nt_path_normpath = getattr(nt, '_path_normpath', None)
+        except Exception:
+            nt_path_normpath = None
+
+        for test, expected in [
+            ('C:\\', 'C:\\'),
+            ('../abc', '..\\abc'),
+            ('../../abc', '..\\..\\abc'),
+            ('./abc', 'abc'),
+            ('./../abc', '..\\abc'),
+            ('\\abc', '\\abc'),
+            ('C:abc', 'C:abc'),
+            ('C:abc\\..\\', 'C:'),
+            ('C:abc\\..\\def\\..\\..\\', 'C:..'),
+            ('C:\\abc\\xyz///..\\def\\', 'C:\\abc\\def'),
+            ('abc/../', '.'),
+            ('./abc/../', '.'),
+        ]:
+            result = sanitize_path(test)
+            assert result == expected, f'{test} was incorrectly resolved'
+            assert result == sanitize_path(result), f'{test} changed after sanitizing again'
+            if nt_path_normpath:
+                assert result == nt_path_normpath(test), f'{test} does not match nt._path_normpath'
+
     def test_sanitize_url(self):
         self.assertEqual(sanitize_url('//foo.bar'), 'http://foo.bar')
         self.assertEqual(sanitize_url('httpss://foo.bar'), 'https://foo.bar')
diff --git a/yt_dlp/utils/_utils.py b/yt_dlp/utils/_utils.py
index 699bf1e7f..17d8424c4 100644
--- a/yt_dlp/utils/_utils.py
+++ b/yt_dlp/utils/_utils.py
@@ -685,7 +685,8 @@ def _sanitize_path_parts(parts):
         elif part == '..':
             if sanitized_parts and sanitized_parts[-1] != '..':
                 sanitized_parts.pop()
-            sanitized_parts.append('..')
+            else:
+                sanitized_parts.append('..')
             continue
         # Replace invalid segments with `#`
         # - trailing dots and spaces (`asdf...` => `asdf..#`)
@@ -702,7 +703,8 @@ def sanitize_path(s, force=False):
         if not force:
             return s
         root = '/' if s.startswith('/') else ''
-        return root + '/'.join(_sanitize_path_parts(s.split('/')))
+        path = '/'.join(_sanitize_path_parts(s.split('/')))
+        return root + path if root or path else '.'
 
     normed = s.replace('/', '\\')
 
@@ -721,7 +723,8 @@ def sanitize_path(s, force=False):
         root = '\\' if normed[:1] == '\\' else ''
         parts = normed.split('\\')
 
-    return root + '\\'.join(_sanitize_path_parts(parts))
+    path = '\\'.join(_sanitize_path_parts(parts))
+    return root + path if root or path else '.'
 
 
 def sanitize_url(url, *, scheme='http'):