From a8f488aa7267510e953979175d8d9045120d0291 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 14 Apr 2025 17:35:52 +0300
Subject: [PATCH 01/11] gh-81793: Always call linkat() from os.link(), if
 available

This fixes os.link() on platforms (like Linux and OpenIndiana) where the
system link() function does not follow symlinks.

* On Linux and OpenIndiana, it now follows symlinks by default and if
  follow_symlinks=True is specified.
* On Windows, it now raises error if follow_symlinks=True is passed.
* On macOS, it now raises error if follow_symlinks=False is passed and
  the system linkat() function is not available at runtime.
* On other platforms, it now raises error if follow_symlinks is passed
  with a value that does not match the system link() function behavior
  if if the behavior is not known.

Co-authored-by: Joachim Henke <37883863+jo-he@users.noreply.github.com>
Co-authored-by: Thomas Kluyver <takowl@gmail.com>
---
 Doc/library/os.rst                            |  1 +
 Lib/test/test_posix.py                        | 39 +++++++++
 ...5-04-14-17-24-50.gh-issue-81793.OhRTTT.rst |  7 ++
 Modules/clinic/posixmodule.c.h                |  4 +-
 Modules/posixmodule.c                         | 87 +++++++++----------
 5 files changed, 91 insertions(+), 47 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 54a5d3b98e8662..1e54cfec609bd2 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -2338,6 +2338,7 @@ features:
    This function can support specifying *src_dir_fd* and/or *dst_dir_fd* to
    supply :ref:`paths relative to directory descriptors <dir_fd>`, and :ref:`not
    following symlinks <follow_symlinks>`.
+   The default value of *follow_symlinks* is ``False`` on Windows.
 
    .. audit-event:: os.link src,dst,src_dir_fd,dst_dir_fd os.link
 
diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index c9cbe1541e733e..6e077eecea2aed 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -1521,6 +1521,45 @@ def test_pidfd_open(self):
         self.assertEqual(cm.exception.errno, errno.EINVAL)
         os.close(os.pidfd_open(os.getpid(), 0))
 
+    @unittest.skipUnless(hasattr(os, "link"), "test needs os.link()")
+    def test_link_follow_symlinks(self):
+        orig = os_helper.TESTFN
+        symlink = orig + 'symlink'
+        posix.symlink(orig, symlink)
+        self.addCleanup(os_helper.unlink, symlink)
+
+        link = orig + 'link'
+        posix.link(symlink, link)
+        self.addCleanup(os_helper.unlink, link)
+        default_follow = sys.platform.startswith(('darwin', 'freebsd', 'netbsd', 'openbsd', 'dragonfly'))
+        default_no_follow = sys.platform.startswith(('win32', 'linux', 'sunos5'))
+        if os.link in os.supports_follow_symlinks or default_follow:
+            self.assertEqual(posix.lstat(link), posix.lstat(orig))
+        elif default_no_follow:
+            self.assertEqual(posix.lstat(link), posix.lstat(symlink))
+
+        # follow_symlinks=False -> duplicate the symlink itself
+        link_nofollow = orig + 'link_nofollow'
+        try:
+            posix.link(symlink, link_nofollow, follow_symlinks=False)
+        except NotImplementedError:
+            if os.link in os.supports_follow_symlinks or default_no_follow:
+                raise
+        else:
+            self.addCleanup(os_helper.unlink, link_nofollow)
+            self.assertEqual(posix.lstat(link_nofollow), posix.lstat(symlink))
+
+        # follow_symlinks=True -> duplicate the target file
+        link_following = orig + 'link_following'
+        try:
+            posix.link(symlink, link_following, follow_symlinks=True)
+        except NotImplementedError:
+            if os.link in os.supports_follow_symlinks or default_follow:
+                raise
+        else:
+            self.addCleanup(os_helper.unlink, link_following)
+            self.assertEqual(posix.lstat(link_following), posix.lstat(orig))
+
 
 # tests for the posix *at functions follow
 class TestPosixDirFd(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
new file mode 100644
index 00000000000000..15fe8ba9e9a902
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
@@ -0,0 +1,7 @@
+Fix :func:`os.link` on platforms (like Linux and OpenIndiana) where the
+system :c:finc:`!link` function does not follow symlinks. On Linux and
+OpenIndiana, it now follows symlinks by default and if
+``follow_symlinks=True`` is specified. On Windows, it now raises error if
+``follow_symlinks=True`` is passed. On macOS, it now raises error if
+``follow_symlinks=False`` is passed and the system :c:finc:`!linkat`
+function is not available at runtime.
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index d03f68ab8fb9aa..2c0f4d9401e2ee 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -1530,7 +1530,7 @@ os_link(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwn
     path_t dst = PATH_T_INITIALIZE_P("link", "dst", 0, 0, 0, 0);
     int src_dir_fd = DEFAULT_DIR_FD;
     int dst_dir_fd = DEFAULT_DIR_FD;
-    int follow_symlinks = 1;
+    int follow_symlinks = -1;
 
     args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser,
             /*minpos*/ 2, /*maxpos*/ 2, /*minkw*/ 0, /*varpos*/ 0, argsbuf);
@@ -13398,4 +13398,4 @@ os__emscripten_debugger(PyObject *module, PyObject *Py_UNUSED(ignored))
 #ifndef OS__EMSCRIPTEN_DEBUGGER_METHODDEF
     #define OS__EMSCRIPTEN_DEBUGGER_METHODDEF
 #endif /* !defined(OS__EMSCRIPTEN_DEBUGGER_METHODDEF) */
-/*[clinic end generated code: output=35dd8edb53b50537 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=27f684c2f99c83c6 input=a9049054013a1b77]*/
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index b7300def8dc75f..f18b785de6d3af 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -427,7 +427,7 @@ extern char *ctermid_r(char *);
 /* Something to implement in autoconf, not present in autoconf 2.69 */
 #  define HAVE_STRUCT_STAT_ST_FSTYPE 1
 #endif
-
+#undef HAVE_LINKAT
 
 // --- Apple __builtin_available() macros -----------------------------------
 
@@ -4323,7 +4323,7 @@ os.link
     *
     src_dir_fd : dir_fd = None
     dst_dir_fd : dir_fd = None
-    follow_symlinks: bool = True
+    follow_symlinks: bool(c_default="-1", py_default="(os.name != 'nt')") = PLACEHOLDER
 
 Create a hard link to a file.
 
@@ -4341,25 +4341,48 @@ src_dir_fd, dst_dir_fd, and follow_symlinks may not be implemented on your
 static PyObject *
 os_link_impl(PyObject *module, path_t *src, path_t *dst, int src_dir_fd,
              int dst_dir_fd, int follow_symlinks)
-/*[clinic end generated code: output=7f00f6007fd5269a input=b0095ebbcbaa7e04]*/
+/*[clinic end generated code: output=7f00f6007fd5269a input=f6a681a558380a15]*/
 {
 #ifdef MS_WINDOWS
     BOOL result = FALSE;
 #else
     int result;
 #endif
-#if defined(HAVE_LINKAT)
-    int linkat_unavailable = 0;
-#endif
 
-#ifndef HAVE_LINKAT
-    if ((src_dir_fd != DEFAULT_DIR_FD) || (dst_dir_fd != DEFAULT_DIR_FD)) {
-        argument_unavailable_error("link", "src_dir_fd and dst_dir_fd");
-        return NULL;
+#ifdef HAVE_LINKAT
+    if (HAVE_LINKAT_RUNTIME) {
+        if (follow_symlinks < 0) {
+            follow_symlinks = 1;
+        }
     }
+    else
 #endif
+    {
+        if ((src_dir_fd != DEFAULT_DIR_FD) || (dst_dir_fd != DEFAULT_DIR_FD)) {
+            argument_unavailable_error("link", "src_dir_fd and dst_dir_fd");
+            return NULL;
+        }
+/* See issue 41355: link() on Linux works like linkat without AT_SYMLINK_FOLLOW,
+   but on Mac it works like linkat *with* AT_SYMLINK_FOLLOW. */
+#if defined(MS_WINDOWS) || defined(__linux__) || (defined(__sun) && defined(__SVR4))
+        if (follow_symlinks == 1) {
+            argument_unavailable_error("link", "follow_symlinks=True");
+            return NULL;
+        }
+#elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
+        if (follow_symlinks == 0) {
+            argument_unavailable_error("link", "follow_symlinks=False");
+            return NULL;
+        }
+#else
+        if (follow_symlinks >= 0) {
+            argument_unavailable_error("link", "follow_symlinks");
+            return NULL;
+        }
+#endif
+    }
 
-#ifndef MS_WINDOWS
+#ifdef MS_WINDOWS
     if ((src->narrow && dst->wide) || (src->wide && dst->narrow)) {
         PyErr_SetString(PyExc_NotImplementedError,
                         "link: src and dst must be the same type");
@@ -4383,44 +4406,18 @@ os_link_impl(PyObject *module, path_t *src, path_t *dst, int src_dir_fd,
 #else
     Py_BEGIN_ALLOW_THREADS
 #ifdef HAVE_LINKAT
-    if ((src_dir_fd != DEFAULT_DIR_FD) ||
-        (dst_dir_fd != DEFAULT_DIR_FD) ||
-        (!follow_symlinks)) {
-
-        if (HAVE_LINKAT_RUNTIME) {
-
-            result = linkat(src_dir_fd, src->narrow,
-                dst_dir_fd, dst->narrow,
-                follow_symlinks ? AT_SYMLINK_FOLLOW : 0);
-
-        }
-#ifdef __APPLE__
-        else {
-            if (src_dir_fd == DEFAULT_DIR_FD && dst_dir_fd == DEFAULT_DIR_FD) {
-                /* See issue 41355: This matches the behaviour of !HAVE_LINKAT */
-                result = link(src->narrow, dst->narrow);
-            } else {
-                linkat_unavailable = 1;
-            }
-        }
-#endif
+    if (HAVE_LINKAT_RUNTIME) {
+        result = linkat(src_dir_fd, src->narrow,
+            dst_dir_fd, dst->narrow,
+            follow_symlinks ? AT_SYMLINK_FOLLOW : 0);
     }
     else
-#endif /* HAVE_LINKAT */
+#endif
+    {
+        /* linkat not available */
         result = link(src->narrow, dst->narrow);
-    Py_END_ALLOW_THREADS
-
-#ifdef HAVE_LINKAT
-    if (linkat_unavailable) {
-        /* Either or both dir_fd arguments were specified */
-        if (src_dir_fd  != DEFAULT_DIR_FD) {
-            argument_unavailable_error("link", "src_dir_fd");
-        } else {
-            argument_unavailable_error("link", "dst_dir_fd");
-        }
-        return NULL;
     }
-#endif
+    Py_END_ALLOW_THREADS
 
     if (result)
         return path_error2(src, dst);

From 4ba224e4e1c5c385b416173218a6bbe1eef6bc7f Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 14 Apr 2025 18:05:48 +0300
Subject: [PATCH 02/11] Fix typo and regenerate clinic files.

---
 .../Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst     | 4 ++--
 Modules/clinic/posixmodule.c.h                                | 4 ++--
 Modules/posixmodule.c                                         | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
index 15fe8ba9e9a902..f0246b181bdd2e 100644
--- a/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
+++ b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
@@ -1,7 +1,7 @@
 Fix :func:`os.link` on platforms (like Linux and OpenIndiana) where the
-system :c:finc:`!link` function does not follow symlinks. On Linux and
+system :c:func:`!link` function does not follow symlinks. On Linux and
 OpenIndiana, it now follows symlinks by default and if
 ``follow_symlinks=True`` is specified. On Windows, it now raises error if
 ``follow_symlinks=True`` is passed. On macOS, it now raises error if
-``follow_symlinks=False`` is passed and the system :c:finc:`!linkat`
+``follow_symlinks=False`` is passed and the system :c:func:`!linkat`
 function is not available at runtime.
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index 2c0f4d9401e2ee..0d970a6a050f5c 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -1471,7 +1471,7 @@ os_getcwdb(PyObject *module, PyObject *Py_UNUSED(ignored))
 
 PyDoc_STRVAR(os_link__doc__,
 "link($module, /, src, dst, *, src_dir_fd=None, dst_dir_fd=None,\n"
-"     follow_symlinks=True)\n"
+"     follow_symlinks=(os.name != \'nt\'))\n"
 "--\n"
 "\n"
 "Create a hard link to a file.\n"
@@ -13398,4 +13398,4 @@ os__emscripten_debugger(PyObject *module, PyObject *Py_UNUSED(ignored))
 #ifndef OS__EMSCRIPTEN_DEBUGGER_METHODDEF
     #define OS__EMSCRIPTEN_DEBUGGER_METHODDEF
 #endif /* !defined(OS__EMSCRIPTEN_DEBUGGER_METHODDEF) */
-/*[clinic end generated code: output=27f684c2f99c83c6 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=12932e9cd3f9afb9 input=a9049054013a1b77]*/
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index f18b785de6d3af..70c235278015c4 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -4341,7 +4341,7 @@ src_dir_fd, dst_dir_fd, and follow_symlinks may not be implemented on your
 static PyObject *
 os_link_impl(PyObject *module, path_t *src, path_t *dst, int src_dir_fd,
              int dst_dir_fd, int follow_symlinks)
-/*[clinic end generated code: output=7f00f6007fd5269a input=f6a681a558380a15]*/
+/*[clinic end generated code: output=7f00f6007fd5269a input=1d5e602d115fed7b]*/
 {
 #ifdef MS_WINDOWS
     BOOL result = FALSE;

From 5881b2a0eb6ba177468b750bf8b2026c89743d36 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 14 Apr 2025 18:51:54 +0300
Subject: [PATCH 03/11] Fix OpenIndiana.

---
 Lib/test/test_posix.py                                      | 5 +++--
 .../Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst   | 6 +++---
 Modules/posixmodule.c                                       | 4 ++--
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index 6e077eecea2aed..7e093d1c850d81 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -1531,8 +1531,9 @@ def test_link_follow_symlinks(self):
         link = orig + 'link'
         posix.link(symlink, link)
         self.addCleanup(os_helper.unlink, link)
-        default_follow = sys.platform.startswith(('darwin', 'freebsd', 'netbsd', 'openbsd', 'dragonfly'))
-        default_no_follow = sys.platform.startswith(('win32', 'linux', 'sunos5'))
+        default_follow = sys.platform.startswith(
+            ('darwin', 'freebsd', 'netbsd', 'openbsd', 'dragonfly', 'sunos5'))
+        default_no_follow = sys.platform.startswith(('win32', 'linux'))
         if os.link in os.supports_follow_symlinks or default_follow:
             self.assertEqual(posix.lstat(link), posix.lstat(orig))
         elif default_no_follow:
diff --git a/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
index f0246b181bdd2e..933c4b63181d12 100644
--- a/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
+++ b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
@@ -1,6 +1,6 @@
-Fix :func:`os.link` on platforms (like Linux and OpenIndiana) where the
-system :c:func:`!link` function does not follow symlinks. On Linux and
-OpenIndiana, it now follows symlinks by default and if
+Fix :func:`os.link` on platforms (like Linux) where the
+system :c:func:`!link` function does not follow symlinks. On Linux,
+it now follows symlinks by default and if
 ``follow_symlinks=True`` is specified. On Windows, it now raises error if
 ``follow_symlinks=True`` is passed. On macOS, it now raises error if
 ``follow_symlinks=False`` is passed and the system :c:func:`!linkat`
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 70c235278015c4..39c5369671b9f8 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -4364,12 +4364,12 @@ os_link_impl(PyObject *module, path_t *src, path_t *dst, int src_dir_fd,
         }
 /* See issue 41355: link() on Linux works like linkat without AT_SYMLINK_FOLLOW,
    but on Mac it works like linkat *with* AT_SYMLINK_FOLLOW. */
-#if defined(MS_WINDOWS) || defined(__linux__) || (defined(__sun) && defined(__SVR4))
+#if defined(MS_WINDOWS) || defined(__linux__)
         if (follow_symlinks == 1) {
             argument_unavailable_error("link", "follow_symlinks=True");
             return NULL;
         }
-#elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
+#elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__) || (defined(__sun) && defined(__SVR4))
         if (follow_symlinks == 0) {
             argument_unavailable_error("link", "follow_symlinks=False");
             return NULL;

From d2f233b9450724238aadbbf1126872d1b9209acc Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 14 Apr 2025 19:05:12 +0300
Subject: [PATCH 04/11] Fix test_inspect.

---
 Lib/test/test_inspect/test_inspect.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py
index daae990458d708..05f97337b0fa69 100644
--- a/Lib/test/test_inspect/test_inspect.py
+++ b/Lib/test/test_inspect/test_inspect.py
@@ -5799,7 +5799,7 @@ def test_operator_module_has_signatures(self):
         self._test_module_has_signatures(operator)
 
     def test_os_module_has_signatures(self):
-        unsupported_signature = {'chmod', 'utime'}
+        unsupported_signature = {'chmod', 'link', 'utime'}
         unsupported_signature |= {name for name in
             ['get_terminal_size', 'posix_spawn', 'posix_spawnp',
              'register_at_fork', 'startfile']

From 95f55e3192cde90fe34ce05fe0fcae9246a323ec Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 14 Apr 2025 19:08:12 +0300
Subject: [PATCH 05/11] Enable linkat().

---
 Modules/posixmodule.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 39c5369671b9f8..a6e18ffd8e1026 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -427,7 +427,7 @@ extern char *ctermid_r(char *);
 /* Something to implement in autoconf, not present in autoconf 2.69 */
 #  define HAVE_STRUCT_STAT_ST_FSTYPE 1
 #endif
-#undef HAVE_LINKAT
+
 
 // --- Apple __builtin_available() macros -----------------------------------
 

From 2eeb438c1289ad5962b68ed21ec1b1f8724b0661 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 14 Apr 2025 20:49:29 +0300
Subject: [PATCH 06/11] Apply suggestions from code review

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
---
 .../Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst   | 6 +++---
 Modules/posixmodule.c                                       | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
index 933c4b63181d12..842e973b821744 100644
--- a/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
+++ b/Misc/NEWS.d/next/Library/2025-04-14-17-24-50.gh-issue-81793.OhRTTT.rst
@@ -1,7 +1,7 @@
 Fix :func:`os.link` on platforms (like Linux) where the
 system :c:func:`!link` function does not follow symlinks. On Linux,
-it now follows symlinks by default and if
-``follow_symlinks=True`` is specified. On Windows, it now raises error if
-``follow_symlinks=True`` is passed. On macOS, it now raises error if
+it now follows symlinks by default or if
+``follow_symlinks=True`` is specified. On Windows, it now raises an error if
+``follow_symlinks=True`` is passed. On macOS, it now raises an error if
 ``follow_symlinks=False`` is passed and the system :c:func:`!linkat`
 function is not available at runtime.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index a6e18ffd8e1026..3512e6de5e9ece 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -4362,7 +4362,7 @@ os_link_impl(PyObject *module, path_t *src, path_t *dst, int src_dir_fd,
             argument_unavailable_error("link", "src_dir_fd and dst_dir_fd");
             return NULL;
         }
-/* See issue 41355: link() on Linux works like linkat without AT_SYMLINK_FOLLOW,
+/* See issue 85527: link() on Linux works like linkat without AT_SYMLINK_FOLLOW,
    but on Mac it works like linkat *with* AT_SYMLINK_FOLLOW. */
 #if defined(MS_WINDOWS) || defined(__linux__)
         if (follow_symlinks == 1) {

From b4be5269d76ecf29069eb66114a8ffbc183b0b53 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 15 Apr 2025 10:03:21 +0300
Subject: [PATCH 07/11] Use subTest().

---
 Lib/test/test_posix.py | 64 ++++++++++++++++++++++--------------------
 1 file changed, 34 insertions(+), 30 deletions(-)

diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index 7e093d1c850d81..bb18e49c9e3f82 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -1523,43 +1523,47 @@ def test_pidfd_open(self):
 
     @unittest.skipUnless(hasattr(os, "link"), "test needs os.link()")
     def test_link_follow_symlinks(self):
+        default_follow = sys.platform.startswith(
+            ('darwin', 'freebsd', 'netbsd', 'openbsd', 'dragonfly', 'sunos5'))
+        default_no_follow = sys.platform.startswith(('win32', 'linux'))
         orig = os_helper.TESTFN
         symlink = orig + 'symlink'
         posix.symlink(orig, symlink)
         self.addCleanup(os_helper.unlink, symlink)
 
-        link = orig + 'link'
-        posix.link(symlink, link)
-        self.addCleanup(os_helper.unlink, link)
-        default_follow = sys.platform.startswith(
-            ('darwin', 'freebsd', 'netbsd', 'openbsd', 'dragonfly', 'sunos5'))
-        default_no_follow = sys.platform.startswith(('win32', 'linux'))
-        if os.link in os.supports_follow_symlinks or default_follow:
-            self.assertEqual(posix.lstat(link), posix.lstat(orig))
-        elif default_no_follow:
-            self.assertEqual(posix.lstat(link), posix.lstat(symlink))
+        with self.subTest('no follow_symlinks'):
+            # no follow_symlinks -> platform depending
+            link = orig + 'link'
+            posix.link(symlink, link)
+            self.addCleanup(os_helper.unlink, link)
+            if os.link in os.supports_follow_symlinks or default_follow:
+                self.assertEqual(posix.lstat(link), posix.lstat(orig))
+            elif default_no_follow:
+                self.assertEqual(posix.lstat(link), posix.lstat(symlink))
 
-        # follow_symlinks=False -> duplicate the symlink itself
-        link_nofollow = orig + 'link_nofollow'
-        try:
-            posix.link(symlink, link_nofollow, follow_symlinks=False)
-        except NotImplementedError:
-            if os.link in os.supports_follow_symlinks or default_no_follow:
-                raise
-        else:
-            self.addCleanup(os_helper.unlink, link_nofollow)
-            self.assertEqual(posix.lstat(link_nofollow), posix.lstat(symlink))
+        with self.subTest('follow_symlinks=False'):
+            # follow_symlinks=False -> duplicate the symlink itself
+            link = orig + 'link_nofollow'
+            try:
+                posix.link(symlink, link, follow_symlinks=False)
+            except NotImplementedError:
+                if os.link in os.supports_follow_symlinks or default_no_follow:
+                    raise
+            else:
+                self.addCleanup(os_helper.unlink, link)
+                self.assertEqual(posix.lstat(link), posix.lstat(symlink))
 
-        # follow_symlinks=True -> duplicate the target file
-        link_following = orig + 'link_following'
-        try:
-            posix.link(symlink, link_following, follow_symlinks=True)
-        except NotImplementedError:
-            if os.link in os.supports_follow_symlinks or default_follow:
-                raise
-        else:
-            self.addCleanup(os_helper.unlink, link_following)
-            self.assertEqual(posix.lstat(link_following), posix.lstat(orig))
+        with self.subTest('follow_symlinks=True'):
+            # follow_symlinks=True -> duplicate the target file
+            link = orig + 'link_following'
+            try:
+                posix.link(symlink, link, follow_symlinks=True)
+            except NotImplementedError:
+                if os.link in os.supports_follow_symlinks or default_follow:
+                    raise
+            else:
+                self.addCleanup(os_helper.unlink, link)
+                self.assertEqual(posix.lstat(link), posix.lstat(orig))
 
 
 # tests for the posix *at functions follow

From 80128e381b97ebccfe9c36d120afff0c528a9d40 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 15 Apr 2025 12:02:15 +0300
Subject: [PATCH 08/11] Disable linkat() on WASI.

---
 Modules/posixmodule.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 3512e6de5e9ece..909ecd502d9eef 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -573,7 +573,11 @@ extern char *ctermid_r(char *);
 #  define HAVE_FACCESSAT_RUNTIME 1
 #  define HAVE_FCHMODAT_RUNTIME 1
 #  define HAVE_FCHOWNAT_RUNTIME 1
+#ifdef __wasi__
+#  define HAVE_LINKAT_RUNTIME 0
+# else
 #  define HAVE_LINKAT_RUNTIME 1
+# endif
 #  define HAVE_FDOPENDIR_RUNTIME 1
 #  define HAVE_MKDIRAT_RUNTIME 1
 #  define HAVE_RENAMEAT_RUNTIME 1

From a45dfd9e18e44d43ef1bae00c0e2f2293c3dbe3f Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 15 Apr 2025 18:18:53 +0300
Subject: [PATCH 09/11] Test how link() actually works on WASI.

---
 Lib/test/test_posix.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index bb18e49c9e3f82..3015e579243ad8 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -1540,6 +1540,9 @@ def test_link_follow_symlinks(self):
                 self.assertEqual(posix.lstat(link), posix.lstat(orig))
             elif default_no_follow:
                 self.assertEqual(posix.lstat(link), posix.lstat(symlink))
+            if sys.platform.startswith('wasi'):
+                self.assertEqual(posix.lstat(link), posix.lstat(orig))
+                self.assertEqual(posix.lstat(link), posix.lstat(symlink))
 
         with self.subTest('follow_symlinks=False'):
             # follow_symlinks=False -> duplicate the symlink itself

From 557f1ee014ee27f6f7da7288bc1b365cbee2d6a5 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 15 Apr 2025 18:47:05 +0300
Subject: [PATCH 10/11] Revert "Test how link() actually works on WASI."

This reverts commit a45dfd9e18e44d43ef1bae00c0e2f2293c3dbe3f.
---
 Lib/test/test_posix.py | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index 3015e579243ad8..bb18e49c9e3f82 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -1540,9 +1540,6 @@ def test_link_follow_symlinks(self):
                 self.assertEqual(posix.lstat(link), posix.lstat(orig))
             elif default_no_follow:
                 self.assertEqual(posix.lstat(link), posix.lstat(symlink))
-            if sys.platform.startswith('wasi'):
-                self.assertEqual(posix.lstat(link), posix.lstat(orig))
-                self.assertEqual(posix.lstat(link), posix.lstat(symlink))
 
         with self.subTest('follow_symlinks=False'):
             # follow_symlinks=False -> duplicate the symlink itself

From 2c436fbe85f398efb3921ab2a8c6d9a44f722148 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 21 Apr 2025 10:35:11 +0300
Subject: [PATCH 11/11] Remove redundant checks for same type.

---
 Modules/posixmodule.c | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 909ecd502d9eef..0a0597ebc317a5 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -4386,14 +4386,6 @@ os_link_impl(PyObject *module, path_t *src, path_t *dst, int src_dir_fd,
 #endif
     }
 
-#ifdef MS_WINDOWS
-    if ((src->narrow && dst->wide) || (src->wide && dst->narrow)) {
-        PyErr_SetString(PyExc_NotImplementedError,
-                        "link: src and dst must be the same type");
-        return NULL;
-    }
-#endif
-
     if (PySys_Audit("os.link", "OOii", src->object, dst->object,
                     src_dir_fd == DEFAULT_DIR_FD ? -1 : src_dir_fd,
                     dst_dir_fd == DEFAULT_DIR_FD ? -1 : dst_dir_fd) < 0) {
@@ -5913,12 +5905,6 @@ internal_rename(path_t *src, path_t *dst, int src_dir_fd, int dst_dir_fd, int is
         return path_error2(src, dst);
 
 #else
-    if ((src->narrow && dst->wide) || (src->wide && dst->narrow)) {
-        PyErr_Format(PyExc_ValueError,
-                     "%s: src and dst must be the same type", function_name);
-        return NULL;
-    }
-
     Py_BEGIN_ALLOW_THREADS
 #ifdef HAVE_RENAMEAT
     if (dir_fd_specified) {
@@ -10591,12 +10577,6 @@ os_symlink_impl(PyObject *module, path_t *src, path_t *dst,
 
 #else
 
-    if ((src->narrow && dst->wide) || (src->wide && dst->narrow)) {
-        PyErr_SetString(PyExc_ValueError,
-            "symlink: src and dst must be the same type");
-        return NULL;
-    }
-
     Py_BEGIN_ALLOW_THREADS
 #ifdef HAVE_SYMLINKAT
     if (dir_fd != DEFAULT_DIR_FD) {