Fix #12084. os.stat on Windows wasn't working properly with relative symlinks.

Use of DeviceIoControl to obtain the symlink path via the reparse tag was
removed. The code now uses GetFinalPathNameByHandle in the case of a
symbolic link and works properly given the added test which creates a symbolic
link and calls os.stat on it from multiple locations.

Victor Stinner also noticed an issue with os.lstat following the os.stat
code path when being passed bytes. The posix_lstat function was adjusted to
properly hook up win32_lstat instead of the previous STAT macro (win32_stat).

Lib/test/support.py

@@ -1490,7 +1490,7 @@ def can_symlink():
     try:
         os.symlink(TESTFN, TESTFN + "can_symlink")
         can = True
-    except (OSError, NotImplementedError):
+    except (OSError, NotImplementedError, AttributeError):
         can = False
     _can_symlink = can
     return can

Lib/test/test_os.py

@@ -1243,6 +1243,51 @@ class Win32SymlinkTests(unittest.TestCase):
         self.assertEqual(os.stat(link), os.stat(target))
         self.assertNotEqual(os.lstat(link), os.stat(link))
 
+        bytes_link = os.fsencode(link)
+        self.assertEqual(os.stat(bytes_link), os.stat(target))
+        self.assertNotEqual(os.lstat(bytes_link), os.stat(bytes_link))
+
+    def test_12084(self):
+        level1 = os.path.abspath(support.TESTFN)
+        level2 = os.path.join(level1, "level2")
+        level3 = os.path.join(level2, "level3")
+        try:
+            os.mkdir(level1)
+            os.mkdir(level2)
+            os.mkdir(level3)
+
+            file1 = os.path.abspath(os.path.join(level1, "file1"))
+
+            with open(file1, "w") as f:
+                f.write("file1")
+
+            orig_dir = os.getcwd()
+            try:
+                os.chdir(level2)
+                link = os.path.join(level2, "link")
+                os.symlink(os.path.relpath(file1), "link")
+                self.assertIn("link", os.listdir(os.getcwd()))
+
+                # Check os.stat calls from the same dir as the link
+                self.assertEqual(os.stat(file1), os.stat("link"))
+
+                # Check os.stat calls from a dir below the link
+                os.chdir(level1)
+                self.assertEqual(os.stat(file1),
+                                 os.stat(os.path.relpath(link)))
+
+                # Check os.stat calls from a dir above the link
+                os.chdir(level3)
+                self.assertEqual(os.stat(file1),
+                                 os.stat(os.path.relpath(link)))
+            finally:
+                os.chdir(orig_dir)
+        except OSError as err:
+            self.fail(err)
+        finally:
+            os.remove(file1)
+            shutil.rmtree(level1)
+
 
 class FSEncodingTests(unittest.TestCase):
     def test_nop(self):

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.2.1 release candidate 2?
 Core and Builtins
 -----------------
 
+- Issue #12084: os.stat on Windows now works properly with relative symbolic
+  links when called from any directory.
+
 - Issue #1195: my_fgets() now always clears errors before calling fgets(). Fix
   the following case: sys.stdin.read() stopped with CTRL+d (end of file),
   raw_input() interrupted by CTRL+c.