bpo-33898: Fix pathlib issues with Windows device paths

Lib/pathlib.py

@@ -115,13 +115,14 @@ class _WindowsFlavour(_Flavour):
     is_supported = (os.name == 'nt')
 
     drive_letters = set('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
-    ext_namespace_prefix = '\\\\?\\'
+    # See https://bugs.python.org/issue33898
+    ext_namespace_prefix = ('\\\\?\\', '\\\\.\\')
 
     reserved_names = (
         {'CON', 'PRN', 'AUX', 'NUL'} |
         {'COM%d' % i for i in range(1, 10)} |
         {'LPT%d' % i for i in range(1, 10)}
-        )
+    )
 
     # Interesting findings about extended paths:
     # - '\\?\c:\a', '//?/c:\a' and '//?/c:/a' are all supported
@@ -141,8 +142,8 @@ def splitroot(self, part, sep=sep):
         else:
             prefix = ''
         third = part[2:3]
-        if (second == sep and first == sep and third != sep):
-            # is a UNC path:
+        if first == second == sep and third != sep:
+            # is a UNC and/or Global path:
             # vvvvvvvvvvvvvvvvvvvvv root
             # \\machine\mountpoint\directory\etc\...
             #            directory ^^^^^^^^^^^^^^
@@ -163,16 +164,32 @@ def splitroot(self, part, sep=sep):
             drv = part[:2]
             part = part[2:]
             first = third
+        # Except for UNC and Global paths, the drive should be
+        # the first component after the local-device prefix.
+        # See https://bugs.python.org/issue33898
+        # All UNC and some of Global paths are parsed in if-condition above.
+        elif (part != sep and prefix and
+              self.casefold('global') not in self.casefold(prefix)):
+            index = part.find(sep)
+            if index != -1:
+                drv = part[:index]
+                part = part[index:]
+                first = part[0:1]
+            else:
+                drv = part
+                part = ''
+                first = ''
         if first == sep:
             root = first
             part = part.lstrip(sep)
         return prefix + drv, root, part
 
     def casefold(self, s):
+        # .lower() is not ideal. See https://bugs.python.org/issue32612
         return s.lower()
 
     def casefold_parts(self, parts):
-        return [p.lower() for p in parts]
+        return [self.casefold(p) for p in parts]
 
     def resolve(self, path, strict=False):
         s = str(path)
@@ -199,13 +216,31 @@ def resolve(self, path, strict=False):
         return None
 
     def _split_extended_path(self, s, ext_prefix=ext_namespace_prefix):
+        # See https://bugs.python.org/issue33898
         prefix = ''
         if s.startswith(ext_prefix):
             prefix = s[:4]
             s = s[4:]
-            if s.startswith('UNC\\'):
-                prefix += s[:3]
-                s = '\\' + s[3:]
+            index = s.find('\\')
+            if index != -1:
+                # Do not assume case sensitivity.
+                # See https://docs.microsoft.com/windows/desktop/FileIO/naming-a-file
+                s1 = self.casefold(s[:index])
+                if s1 == self.casefold('global'):
+                    prefix += s[:6]
+                    # For example, Path('//?/Global/Z:/').drive
+                    if s[8:9] == ':':
+                        prefix += s[6:7]
+                        s = s[7:]
+                    # For example, r'\\?\Global\UNC\server\share'
+                    elif self.casefold(s[7:11]) == self.casefold('unc\\'):
+                        prefix += s[6:10]
+                        s = '\\' + s[10:]
+                    else:
+                        s = '\\' + s[6:]
+                elif s1 == self.casefold('unc'):
+                    prefix += s[:3]
+                    s = '\\' + s[3:]
         return prefix, s
 
     def _ext_to_normal(self, s):

Misc/NEWS.d/next/Windows/2018-08-04-15-04-10.bpo-33898.psrYKd.rst

@@ -0,0 +1,2 @@
+  Fix pathlib issues with parsing Windows device paths
+  starting with //?/ or //./.  Patch by Albina Giliazova.