gh-106045: Fix venv creation from a python executable symlink

Lib/test/test_venv.py

@@ -892,6 +892,49 @@ def test_venvwlauncher(self):
         except subprocess.CalledProcessError:
             self.fail("venvwlauncher.exe did not run %s" % exename)
 
+    @requires_subprocess()
+    @unittest.skipIf(os.name == 'nt', 'not relevant on Windows')
+    @unittest.skipUnless(can_symlink(), 'Needs symlinks')
+    @unittest.skipUnless(sysconfig.get_config_var('HAVE_READLINK'), "Requires HAVE_READLINK support")
+    def test_executable_symlink(self):
+        """
+        Test creation using a symlink to python executable.
+        """
+        rmtree(self.env_dir)
+        exe = pathlib.Path(sys.executable).absolute()
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            symlink_dir = pathlib.Path(tmp_dir).resolve(strict=True)
+            exe_symlink = symlink_dir / exe.name
+            exe_symlink.symlink_to(exe)
+            cmd = [exe_symlink, "-m", "venv", "--without-pip", self.env_dir]
+            subprocess.check_call(cmd)
+        data = self.get_text_file_contents('pyvenv.cfg')
+        path = os.path.dirname(os.path.abspath(sys._base_executable))
+        self.assertIn('home = %s' % path, data)
+        self.assertIn('executable = %s' % exe.resolve(), data)
+
+    @requires_subprocess()
+    @unittest.skipIf(os.name == 'nt', 'not relevant on Windows')
+    @unittest.skipUnless(can_symlink(), 'Needs symlinks')
+    @requireVenvCreate
+    def test_tree_symlink(self):
+        """
+        Test creation using a symlink to python tree.
+        """
+        rmtree(self.env_dir)
+        exe = pathlib.Path(sys._base_executable).absolute()
+        tree = exe.parent.parent
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            symlink_dir = pathlib.Path(tmp_dir).resolve(strict=True)
+            tree_symlink = symlink_dir / tree.name
+            exe_symlink = tree_symlink / exe.relative_to(tree)
+            tree_symlink.symlink_to(tree)
+            cmd = [exe_symlink, "-m", "venv", "--without-pip", self.env_dir]
+            subprocess.check_call(cmd)
+        data = self.get_text_file_contents('pyvenv.cfg')
+        self.assertIn('home = %s' % tree_symlink, data)
+        self.assertIn('executable = %s' % exe.resolve(), data)
+
 
 @requireVenvCreate
 class EnsurePipTest(BaseTest):

Lib/venv/__init__.py

@@ -133,6 +133,40 @@ def _same_path(cls, path1, path2):
         else:
             return path1 == path2
 
+    @classmethod
+    def _getpath_realpath(cls, path):
+        """Mimics getpath.realpath
+
+        It only mimics it for HAVE_READLINK.
+        There are a few differences listed here:
+        - we ensure that we have a resolvable abspath first
+          (i.e. exists and no symlink loop)
+        - we stop if a candidate does not resolve to the same file
+          (this can happen with normpath)
+        """
+        result = os.path.abspath(path)
+        try:
+            real_path = os.path.realpath(result, strict=True)
+        except OSError:
+            logger.warning('Unable to resolve %r real path', result)
+            return result
+        if sysconfig.get_config_var('HAVE_READLINK'):
+            while os.path.islink(result):
+                link = os.readlink(result)
+                if os.path.isabs(link):
+                    candidate = link
+                else:
+                    candidate = os.path.join(os.path.dirname(result), link)
+                    candidate = os.path.normpath(candidate)
+                # shall exists and be the same file as the original one
+                valid = os.path.exists(candidate) and os.path.samefile(real_path, candidate)
+                if not valid:
+                    logger.warning('Stopped resolving %r because %r is not the same file',
+                                   result, candidate)
+                    break
+                result = candidate
+        return result
+
     def ensure_directories(self, env_dir):
         """
         Create the directories for the environment.
@@ -163,7 +197,8 @@ def create_if_needed(d):
                              'Python interpreter. Provide an explicit path or '
                              'check that your PATH environment variable is '
                              'correctly set.')
-        dirname, exename = os.path.split(os.path.abspath(executable))
+        # only resolve executable symlinks, not the full chain, see gh-106045
+        dirname, exename = os.path.split(self._getpath_realpath(executable))
         if sys.platform == 'win32':
             # Always create the simplest name in the venv. It will either be a
             # link back to executable, or a copy of the appropriate launcher

Misc/ACKS

@@ -419,6 +419,7 @@ Eric Daniel
 Scott David Daniels
 Derzsi Dániel
 Lawrence D'Anna
+Matthieu Darbois
 Ben Darnell
 Kushal Das
 Jonathan Dasteel

Misc/NEWS.d/next/Library/2024-02-10-11-41-42.gh-issue-106045.eVZFt2.rst

@@ -0,0 +1,2 @@
+Fix ``venv`` creation from a python executable symlink. Patch by Matthieu
+Darbois.