bpo-45582: Port getpath[p].c to Python (GH-29041)

The getpath.py file is frozen at build time and executed as code over a namespace. It is never imported, nor is it meant to be importable or reusable. However, it should be easier to read, modify, and patch than the previous code.

This commit attempts to preserve every previously tested quirk, but these may be changed in the future to better align platforms.

Lib/ntpath.py

@@ -70,7 +70,7 @@ def isabs(s):
         if s.replace('/', '\\').startswith('\\\\?\\'):
             return True
     s = splitdrive(s)[1]
-    return len(s) > 0 and s[0] in _get_bothseps(s)
+    return len(s) > 0 and s[0] and s[0] in _get_bothseps(s)
 
 
 # Join two (or more) paths.
@@ -268,11 +268,13 @@ def ismount(path):
     root, rest = splitdrive(path)
     if root and root[0] in seps:
         return (not rest) or (rest in seps)
-    if rest in seps:
+    if rest and rest in seps:
         return True
 
     if _getvolumepathname:
-        return path.rstrip(seps) == _getvolumepathname(path).rstrip(seps)
+        x = path.rstrip(seps)
+        y =_getvolumepathname(path).rstrip(seps)
+        return x.casefold() == y.casefold()
     else:
         return False
 
@@ -459,56 +461,68 @@ def expandvars(path):
 # Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A\B.
 # Previously, this function also truncated pathnames to 8+3 format,
 # but as this module is called "ntpath", that's obviously wrong!
+try:
+    from nt import _path_normpath
 
-def normpath(path):
-    """Normalize path, eliminating double slashes, etc."""
-    path = os.fspath(path)
-    if isinstance(path, bytes):
-        sep = b'\\'
-        altsep = b'/'
-        curdir = b'.'
-        pardir = b'..'
-        special_prefixes = (b'\\\\.\\', b'\\\\?\\')
-    else:
-        sep = '\\'
-        altsep = '/'
-        curdir = '.'
-        pardir = '..'
-        special_prefixes = ('\\\\.\\', '\\\\?\\')
-    if path.startswith(special_prefixes):
-        # in the case of paths with these prefixes:
-        # \\.\ -> device names
-        # \\?\ -> literal paths
-        # do not do any normalization, but return the path
-        # unchanged apart from the call to os.fspath()
-        return path
-    path = path.replace(altsep, sep)
-    prefix, path = splitdrive(path)
+except ImportError:
+    def normpath(path):
+        """Normalize path, eliminating double slashes, etc."""
+        path = os.fspath(path)
+        if isinstance(path, bytes):
+            sep = b'\\'
+            altsep = b'/'
+            curdir = b'.'
+            pardir = b'..'
+            special_prefixes = (b'\\\\.\\', b'\\\\?\\')
+        else:
+            sep = '\\'
+            altsep = '/'
+            curdir = '.'
+            pardir = '..'
+            special_prefixes = ('\\\\.\\', '\\\\?\\')
+        if path.startswith(special_prefixes):
+            # in the case of paths with these prefixes:
+            # \\.\ -> device names
+            # \\?\ -> literal paths
+            # do not do any normalization, but return the path
+            # unchanged apart from the call to os.fspath()
+            return path
+        path = path.replace(altsep, sep)
+        prefix, path = splitdrive(path)
 
-    # collapse initial backslashes
-    if path.startswith(sep):
-        prefix += sep
-        path = path.lstrip(sep)
+        # collapse initial backslashes
+        if path.startswith(sep):
+            prefix += sep
+            path = path.lstrip(sep)
 
-    comps = path.split(sep)
-    i = 0
-    while i < len(comps):
-        if not comps[i] or comps[i] == curdir:
-            del comps[i]
-        elif comps[i] == pardir:
-            if i > 0 and comps[i-1] != pardir:
-                del comps[i-1:i+1]
-                i -= 1
-            elif i == 0 and prefix.endswith(sep):
+        comps = path.split(sep)
+        i = 0
+        while i < len(comps):
+            if not comps[i] or comps[i] == curdir:
                 del comps[i]
+            elif comps[i] == pardir:
+                if i > 0 and comps[i-1] != pardir:
+                    del comps[i-1:i+1]
+                    i -= 1
+                elif i == 0 and prefix.endswith(sep):
+                    del comps[i]
+                else:
+                    i += 1
             else:
                 i += 1
-        else:
-            i += 1
-    # If the path is now empty, substitute '.'
-    if not prefix and not comps:
-        comps.append(curdir)
-    return prefix + sep.join(comps)
+        # If the path is now empty, substitute '.'
+        if not prefix and not comps:
+            comps.append(curdir)
+        return prefix + sep.join(comps)
+
+else:
+    def normpath(path):
+        """Normalize path, eliminating double slashes, etc."""
+        path = os.fspath(path)
+        if isinstance(path, bytes):
+            return os.fsencode(_path_normpath(os.fsdecode(path))) or b"."
+        return _path_normpath(path) or "."
+
 
 def _abspath_fallback(path):
     """Return the absolute version of a path as a fallback function in case