gh-126780: Fix ntpath.normpath() for drive-relative paths (GH-126801)

Lib/test/test_ntpath.py

@@ -347,13 +347,18 @@ class TestNtpath(NtpathTestCase):
 
         tester("ntpath.normpath('..')", r'..')
         tester("ntpath.normpath('.')", r'.')
+        tester("ntpath.normpath('c:.')", 'c:')
         tester("ntpath.normpath('')", r'.')
         tester("ntpath.normpath('/')", '\\')
         tester("ntpath.normpath('c:/')", 'c:\\')
         tester("ntpath.normpath('/../.././..')", '\\')
         tester("ntpath.normpath('c:/../../..')", 'c:\\')
+        tester("ntpath.normpath('/./a/b')", r'\a\b')
+        tester("ntpath.normpath('c:/./a/b')", r'c:\a\b')
         tester("ntpath.normpath('../.././..')", r'..\..\..')
         tester("ntpath.normpath('K:../.././..')", r'K:..\..\..')
+        tester("ntpath.normpath('./a/b')", r'a\b')
+        tester("ntpath.normpath('c:./a/b')", r'c:a\b')
         tester("ntpath.normpath('C:////a/b')", r'C:\a\b')
         tester("ntpath.normpath('//machine/share//a/b')", r'\\machine\share\a\b')
 

Lib/test/test_posixpath.py

@@ -379,6 +379,7 @@ class PosixPathTest(unittest.TestCase):
         ("/.", "/"),
         ("/./", "/"),
         ("/.//.", "/"),
+        ("/./foo/bar", "/foo/bar"),
         ("/foo", "/foo"),
         ("/foo/bar", "/foo/bar"),
         ("//", "//"),
@@ -388,6 +389,7 @@ class PosixPathTest(unittest.TestCase):
         ("///..//./foo/.//bar", "/foo/bar"),
         (".", "."),
         (".//.", "."),
+        ("./foo/bar", "foo/bar"),
         ("..", ".."),
         ("../", ".."),
         ("../foo", "../foo"),

Misc/NEWS.d/next/Library/2024-11-13-19-15-18.gh-issue-126780.ZZqJvI.rst

@@ -0,0 +1 @@
+Fix :func:`os.path.normpath` for drive-relative paths on Windows.

Python/fileutils.c

@@ -2506,16 +2506,6 @@ _Py_normpath_and_size(wchar_t *path, Py_ssize_t size, Py_ssize_t *normsize)
 #endif
 #define SEP_OR_END(x) (IS_SEP(x) || IS_END(x))
 
-    if (p1[0] == L'.' && IS_SEP(&p1[1])) {
-        // Skip leading '.\'
-        path = &path[2];
-        while (IS_SEP(path)) {
-            path++;
-        }
-        p1 = p2 = minP2 = path;
-        lastC = SEP;
-    }
-    else {
     Py_ssize_t drvsize, rootsize;
     _Py_skiproot(path, size, &drvsize, &rootsize);
     if (drvsize || rootsize) {
@@ -2538,6 +2528,17 @@ _Py_normpath_and_size(wchar_t *path, Py_ssize_t size, Py_ssize_t *normsize)
         }
 #endif
     }
+    if (p1[0] == L'.' && SEP_OR_END(&p1[1])) {
+        // Skip leading '.\'
+        lastC = *++p1;
+#ifdef ALTSEP
+        if (lastC == ALTSEP) {
+            lastC = SEP;
+        }
+#endif
+        while (IS_SEP(p1)) {
+            p1++;
+        }
     }
 
     /* if pEnd is specified, check that. Else, check for null terminator */