Fix #1949: zipapp virtual environment creation fails if zipapp path is symlinked

docs/changelog/1949.bugfix.rst

@@ -0,0 +1 @@
+``virtualenv.pyz`` no longer fails when zipapp path contains a symlink - by :user:`HandSonic` and :user:`petamas`.

src/virtualenv/util/zipapp.py

@@ -23,8 +23,12 @@ def extract(full_path, dest):
 
 
 def _get_path_within_zip(full_path):
-    full_path = os.path.abspath(str(full_path))
-    sub_file = full_path[len(ROOT) + 1 :]
+    full_path = os.path.realpath(os.path.abspath(str(full_path)))
+    prefix = f"{ROOT}{os.sep}"
+    if not full_path.startswith(prefix):
+        msg = f"full_path={full_path} should start with prefix={prefix}."
+        raise RuntimeError(msg)
+    sub_file = full_path[len(prefix) :]
     if IS_WIN:
         # paths are always UNIX separators, even on Windows, though __file__ still follows platform default
         sub_file = sub_file.replace(os.sep, "/")

tests/integration/test_zipapp.py

@@ -9,6 +9,7 @@
 from flaky import flaky
 
 from virtualenv.discovery.py_info import PythonInfo
+from virtualenv.info import fs_supports_symlink
 from virtualenv.run import cli_run
 
 HERE = Path(__file__).parent
@@ -83,6 +84,24 @@ def _run(*args):
     return _run
 
 
+@pytest.fixture()
+def call_zipapp_symlink(zipapp, tmp_path, zipapp_test_env, temp_app_data):  # noqa: ARG001
+    def _run(*args):
+        symlinked = zipapp.parent / "symlinked_virtualenv.pyz"
+        symlinked.symlink_to(str(zipapp))
+        cmd = [str(zipapp_test_env), str(symlinked), "-vv", str(tmp_path / "env"), *list(args)]
+        subprocess.check_call(cmd)
+
+    return _run
+
+
+@pytest.mark.skipif(not fs_supports_symlink(), reason="symlink not supported")
+def test_zipapp_in_symlink(capsys, call_zipapp_symlink):
+    call_zipapp_symlink("--reset-app-data")
+    _out, err = capsys.readouterr()
+    assert not err
+
+
 @flaky(max_runs=2, min_passes=1)
 def test_zipapp_help(call_zipapp, capsys):
     call_zipapp("-h")