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

Author: mayeut

Lib/test/test_venv.py

@@ -892,6 +892,57 @@ 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')
+    def test_executable_symlink(self):
+        """
+        Test creation using a symlink to python executable.
+        """
+        rmtree(self.env_dir)
+        with tempfile.TemporaryDirectory() as symlink_dir:
+            executable_symlink = os.path.join(
+                os.path.realpath(symlink_dir),
+                os.path.basename(sys.executable))
+            os.symlink(os.path.abspath(sys.executable), executable_symlink)
+            cmd = [executable_symlink, "-m", "venv", "--without-pip",
+                   self.env_dir]
+            subprocess.check_call(cmd)
+        data = self.get_text_file_contents('pyvenv.cfg')
+        executable = sys._base_executable
+        path = os.path.dirname(executable)
+        self.assertIn('home = %s' % path, data)
+        self.assertIn('executable = %s' %
+                      os.path.realpath(sys.executable), 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)
+        executable_abspath = os.path.abspath(sys._base_executable)
+        tree_abspath = os.path.dirname(os.path.dirname(executable_abspath))
+        with tempfile.TemporaryDirectory() as symlink_dir:
+            tree_symlink = os.path.join(
+                os.path.realpath(symlink_dir),
+                os.path.basename(tree_abspath))
+            executable_symlink = os.path.join(
+                tree_symlink,
+                os.path.basename(os.path.dirname(executable_abspath)),
+                os.path.basename(sys._base_executable))
+            os.symlink(tree_abspath, tree_symlink)
+            cmd = [executable_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' %
+                      os.path.realpath(sys._base_executable), data)
+
 
 @requireVenvCreate
 class EnsurePipTest(BaseTest):

Lib/venv/__init__.py

@@ -163,7 +163,16 @@ 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
+        # we don't want to overwrite the executable used in context
+        executable_ = os.path.abspath(executable)
+        while os.path.islink(executable_):
+            link = os.readlink(executable_)
+            if os.path.isabs(link):
+                executable_ = link
+            else:
+                executable_ = os.path.join(os.path.dirname(executable_), link)
+        dirname, exename = os.path.split(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.