Reset the embed update log when it cannot be read

docs/changelog/3376.bugfix.rst

@@ -0,0 +1,2 @@
+Fall back to the bundled seed wheel and remove the embed update log when the log in the app data folder holds JSON of
+the wrong shape, instead of failing to create the environment - by :user:`pasmud`.

src/virtualenv/seed/wheels/periodic_update.py

@@ -8,6 +8,7 @@
 import os
 import ssl
 import sys
+from contextlib import suppress
 from datetime import datetime, timedelta, timezone
 from itertools import groupby
 from pathlib import Path
@@ -28,7 +29,7 @@
 if TYPE_CHECKING:
     from collections.abc import Generator
 
-    from virtualenv.app_data.base import AppData
+    from virtualenv.app_data.base import AppData, ContentStore
 
 LOGGER = logging.getLogger(__name__)
 GRACE_PERIOD_CI = timedelta(hours=1)  # prevent version switch in the middle of a CI run
@@ -192,8 +193,16 @@ def from_dict(cls, dictionary: dict[str, object] | None) -> UpdateLog:
 
     @classmethod
     def from_app_data(cls, app_data: AppData, distribution: str, for_py_version: str) -> UpdateLog:
-        raw_json = app_data.embed_update_log(distribution, for_py_version).read()
-        return cls.from_dict(raw_json)
+        store: Final[ContentStore] = app_data.embed_update_log(distribution, for_py_version)
+        try:
+            return cls.from_dict(store.read())
+        except (AttributeError, KeyError, TypeError, ValueError):
+            # another virtualenv version or an interrupted run can leave valid JSON of the wrong shape in the shared
+            # app data; drop it as read() drops invalid JSON, since an empty log falls back to the bundled wheel
+            LOGGER.warning("removing malformed embed update log of %s", distribution)
+            with suppress(OSError):  # another process may remove or rewrite the file at the same time
+                store.remove()
+            return cls(None, None, [], None)
 
     def to_dict(self) -> dict[str, object]:
         return {

tests/unit/seed/wheels/test_periodic_update.py

@@ -2,6 +2,7 @@
 
 import hashlib
 import json
+import logging
 import os
 import subprocess
 import sys
@@ -12,7 +13,7 @@
 from itertools import zip_longest
 from pathlib import Path
 from textwrap import dedent
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Final
 from urllib.error import URLError
 
 import pytest
@@ -42,6 +43,8 @@
 
     from pytest_mock import MockerFixture
 
+    from virtualenv.app_data.via_disk_folder import EmbedDistributionUpdateStoreDisk
+
 
 @pytest.fixture(autouse=True)
 def _clear_pypi_info_cache() -> Generator[None, None, None]:
@@ -251,6 +254,39 @@ def test_periodic_update_skip(u_log, mocker, for_py_version, session_app_data, t
     assert result is None
 
 
+@pytest.mark.parametrize(
+    "stored",
+    [
+        pytest.param([1, 2, 3], id="not-a-mapping"),
+        pytest.param("oops", id="string"),
+        pytest.param({"versions": "abc"}, id="versions-not-a-list"),
+        pytest.param({"versions": ["abc"]}, id="version-not-a-mapping"),
+        pytest.param({"completed": 5, "started": None, "versions": []}, id="completed-not-a-datetime"),
+    ],
+)
+def test_periodic_update_drops_malformed_log(
+    stored: list[int] | str | dict[str, str | int | list[str] | None],
+    tmp_path: Path,
+    for_py_version: str,
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    caplog.set_level(logging.WARNING)
+    app_data: Final[AppDataDiskFolder] = AppDataDiskFolder(str(tmp_path))
+    log: Final[EmbedDistributionUpdateStoreDisk] = app_data.embed_update_log("setuptools", for_py_version)
+    log.write(stored)
+    wheel: Final[Wheel | None] = get_embed_wheel("setuptools", for_py_version)
+
+    result: Final[Wheel | None] = periodic_update(
+        "setuptools", None, for_py_version, wheel, [], app_data, False, os.environ
+    )
+
+    assert (result, log.exists(), caplog.messages) == (
+        wheel,
+        False,
+        ["removing malformed embed update log of setuptools"],
+    )
+
+
 _UPDATE_YES = {
     "never_started": UpdateLog(started=None, completed=None, versions=[], periodic=False),
     "started_1_hour": UpdateLog(