[3.7] bpo-31047: Fix ntpath.abspath to trim ending separator (GH-10082)

Lib/ntpath.py

@@ -523,8 +523,8 @@ else:  # use native Windows method on Windows
     def abspath(path):
         """Return the absolute version of a path."""
         try:
-            return _getfullpathname(path)
-        except OSError:
+            return normpath(_getfullpathname(path))
+        except (OSError, ValueError):
             return _abspath_fallback(path)
 
 # realpath is a no-op on systems without islink support

Lib/test/test_ntpath.py

@@ -284,6 +284,8 @@ class TestNtpath(unittest.TestCase):
             tester('ntpath.abspath("")', cwd_dir)
             tester('ntpath.abspath(" ")', cwd_dir + "\\ ")
             tester('ntpath.abspath("?")', cwd_dir + "\\?")
+            drive, _ = ntpath.splitdrive(cwd_dir)
+            tester('ntpath.abspath("/abc/")', drive + "\\abc")
 
     def test_relpath(self):
         tester('ntpath.relpath("a")', 'a')

Misc/NEWS.d/next/Library/2018-10-25-09-37-03.bpo-31047.kBbX8r.rst

@@ -0,0 +1,2 @@
+Fix ``ntpath.abspath`` regression where it didn't remove a trailing
+separator on Windows. Patch by Tim Graham.