From 630df37116b1c5b381984c547ef9d23792ceb464 Mon Sep 17 00:00:00 2001
From: Barney Gale <barney.gale@gmail.com>
Date: Wed, 10 Apr 2024 18:17:18 +0100
Subject: [PATCH] GH-117546: Fix symlink resolution in
 `os.path.realpath('loop/../link')` (#117568)

Continue resolving symlink targets after encountering a symlink loop, which
matches coreutils `realpath` behaviour.
---
 Doc/library/os.path.rst                           |  5 ++---
 Lib/posixpath.py                                  | 15 ++-------------
 Lib/test/test_posixpath.py                        |  2 +-
 ...2024-04-05-13-38-53.gh-issue-117546.lWjhHE.rst |  2 ++
 4 files changed, 7 insertions(+), 17 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-04-05-13-38-53.gh-issue-117546.lWjhHE.rst

diff --git a/Doc/library/os.path.rst b/Doc/library/os.path.rst
index fcf4b6d68e018c..ebeb3bb50b8b1f 100644
--- a/Doc/library/os.path.rst
+++ b/Doc/library/os.path.rst
@@ -409,9 +409,8 @@ the :mod:`glob` module.)
    style names such as ``C:\\PROGRA~1`` to ``C:\\Program Files``.
 
    If a path doesn't exist or a symlink loop is encountered, and *strict* is
-   ``True``, :exc:`OSError` is raised. If *strict* is ``False``, the path is
-   resolved as far as possible and any remainder is appended without checking
-   whether it exists.
+   ``True``, :exc:`OSError` is raised. If *strict* is ``False`` these errors
+   are ignored, and so the result might be missing or otherwise inaccessible.
 
    .. note::
       This function emulates the operating system's procedure for making a path
diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 79e65587e66282..8fd49cdc358908 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -431,11 +431,6 @@ def realpath(filename, *, strict=False):
     # the same links.
     seen = {}
 
-    # Whether we're calling lstat() and readlink() to resolve symlinks. If we
-    # encounter an OSError for a symlink loop in non-strict mode, this is
-    # switched off.
-    querying = True
-
     while rest:
         name = rest.pop()
         if name is None:
@@ -453,9 +448,6 @@ def realpath(filename, *, strict=False):
             newpath = path + name
         else:
             newpath = path + sep + name
-        if not querying:
-            path = newpath
-            continue
         try:
             st = os.lstat(newpath)
             if not stat.S_ISLNK(st.st_mode):
@@ -477,11 +469,8 @@ def realpath(filename, *, strict=False):
             if strict:
                 # Raise OSError(errno.ELOOP)
                 os.stat(newpath)
-            else:
-                # Return already resolved part + rest of the path unchanged.
-                path = newpath
-                querying = False
-                continue
+            path = newpath
+            continue
         seen[newpath] = None # not resolved symlink
         target = os.readlink(newpath)
         if target.startswith(sep):
diff --git a/Lib/test/test_posixpath.py b/Lib/test/test_posixpath.py
index ff78410738022d..248fe2cc5d5ca8 100644
--- a/Lib/test/test_posixpath.py
+++ b/Lib/test/test_posixpath.py
@@ -484,7 +484,7 @@ def test_realpath_symlink_loops(self):
             self.assertEqual(realpath(ABSTFN+"1/../x"), dirname(ABSTFN) + "/x")
             os.symlink(ABSTFN+"x", ABSTFN+"y")
             self.assertEqual(realpath(ABSTFN+"1/../" + basename(ABSTFN) + "y"),
-                             ABSTFN + "y")
+                             ABSTFN + "x")
             self.assertEqual(realpath(ABSTFN+"1/../" + basename(ABSTFN) + "1"),
                              ABSTFN + "1")
 
diff --git a/Misc/NEWS.d/next/Library/2024-04-05-13-38-53.gh-issue-117546.lWjhHE.rst b/Misc/NEWS.d/next/Library/2024-04-05-13-38-53.gh-issue-117546.lWjhHE.rst
new file mode 100644
index 00000000000000..9762991e47a6a4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-04-05-13-38-53.gh-issue-117546.lWjhHE.rst
@@ -0,0 +1,2 @@
+Fix issue where :func:`os.path.realpath` stopped resolving symlinks after
+encountering a symlink loop on POSIX.