fix: Patch get_interpreter to handle missing cache and app_data (#2974)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: esafak

docs/changelog/2972.bugfix.rst

@@ -0,0 +1 @@
+Patch get_interpreter to handle missing cache and app_data - by :user:`esafak`

src/virtualenv/discovery/builtin.py

@@ -77,6 +77,25 @@ def get_interpreter(
     cache=None,
     env: Mapping[str, str] | None = None,
 ) -> PythonInfo | None:
+    """
+    Find an interpreter that matches a given specification.
+
+    :param key: the specification of the interpreter to find
+    :param try_first_with: a list of interpreters to try first
+    :param app_data: the application data folder
+    :param cache: a cache of python information
+    :param env: the environment to use
+    :return: the interpreter if found, otherwise None
+    """
+    if cache is None:
+        # Import locally to avoid a circular dependency
+        from virtualenv.app_data import AppDataDisabled  # noqa: PLC0415
+        from virtualenv.cache import FileCache  # noqa: PLC0415
+
+        if app_data is None:
+            app_data = AppDataDisabled()
+        cache = FileCache(store_factory=app_data.py_info, clearer=app_data.py_info_clear)
+
     spec = PythonSpec.from_string_spec(key)
     LOGGER.info("find interpreter for spec %r", spec)
     proposed_paths = set()

tests/unit/discovery/test_discovery.py

@@ -224,6 +224,18 @@ def test_returns_second_python_specified_when_more_than_one_is_specified_and_env
     assert result == mocker.sentinel.python_from_cli
 
 
+def test_get_interpreter_no_cache_no_app_data():
+    """Test that get_interpreter can be called without cache and app_data."""
+    # A call to a valid interpreter should succeed and return a PythonInfo object.
+    interpreter = get_interpreter(sys.executable, [])
+    assert interpreter is not None
+    assert Path(interpreter.executable).is_file()
+
+    # A call to an invalid interpreter should not fail and should return None.
+    interpreter = get_interpreter("a-python-that-does-not-exist", [])
+    assert interpreter is None
+
+
 def test_discovery_absolute_path_with_try_first(tmp_path):
     good_env = tmp_path / "good"
     bad_env = tmp_path / "bad"