From 211e4c6e9c1ab60bb2577dda6587fbec79f679b2 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Wed, 26 Aug 2020 17:51:44 -0700
Subject: [PATCH] bpo-33660: Fix PosixPath to resolve a relative path on root
 (#21974)

(cherry picked from commit 94ad6c674f7687ef22853cb8d42b440d6b42ddc8)

Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>
---
 Lib/pathlib.py                                           | 5 ++++-
 Lib/test/test_pathlib.py                                 | 9 +++++++++
 .../Library/2018-06-12-23-30-41.bpo-33660.AdDn5Z.rst     | 2 ++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2018-06-12-23-30-41.bpo-33660.AdDn5Z.rst

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index 9f5e27b9117..babc443dd3b 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -329,7 +329,10 @@ class _PosixFlavour(_Flavour):
                     # parent dir
                     path, _, _ = path.rpartition(sep)
                     continue
-                newpath = path + sep + name
+                if path.endswith(sep):
+                    newpath = path + name
+                else:
+                    newpath = path + sep + name
                 if newpath in seen:
                     # Already seen this path
                     path = seen[newpath]
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index 1589282886b..3da35710b9d 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -2347,6 +2347,15 @@ class PosixPathTest(_BasePathTest, unittest.TestCase):
         st = os.stat(join('other_new_file'))
         self.assertEqual(stat.S_IMODE(st.st_mode), 0o644)
 
+    def test_resolve_root(self):
+        current_directory = os.getcwd()
+        try:
+            os.chdir('/')
+            p = self.cls('spam')
+            self.assertEqual(str(p.resolve()), '/spam')
+        finally:
+            os.chdir(current_directory)
+
     def test_touch_mode(self):
         old_mask = os.umask(0)
         self.addCleanup(os.umask, old_mask)
diff --git a/Misc/NEWS.d/next/Library/2018-06-12-23-30-41.bpo-33660.AdDn5Z.rst b/Misc/NEWS.d/next/Library/2018-06-12-23-30-41.bpo-33660.AdDn5Z.rst
new file mode 100644
index 00000000000..cce3dbb1c6e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-06-12-23-30-41.bpo-33660.AdDn5Z.rst
@@ -0,0 +1,2 @@
+Fix pathlib.PosixPath to resolve a relative path located on the root
+directory properly.