Pytest auto-close plugin for Datasette instances

Installs a pytest11 entry point so that every Datasette() constructed
inside a pytest_runtest_call phase is auto-closed at the end of the test.
Fixture-scoped instances are untouched. Opt out via the
datasette_autoclose = false ini option.

This gives large test suites a safety net against FD exhaustion and leaked
write threads from the now-default temp-disk internal database without
requiring every existing test to be rewritten.

Refs #2692

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

datasette/_pytest_plugin.py

@@ -0,0 +1,78 @@
+"""
+Pytest plugin that automatically closes any Datasette instances constructed
+inside a test body. Fixture-scoped instances survive.
+
+Registered as a pytest11 entry point in pyproject.toml so that downstream
+projects using Datasette get the same FD-safety net for their own tests.
+
+Opt out by setting ``datasette_autoclose = false`` in pytest.ini (or the
+equivalent ini file).
+"""
+
+from __future__ import annotations
+
+import contextvars
+import weakref
+
+import pytest
+
+from datasette.app import Datasette
+
+_active_instances: contextvars.ContextVar[list | None] = contextvars.ContextVar(
+    "datasette_active_instances", default=None
+)
+
+_original_init = Datasette.__init__
+
+
+def _tracking_init(self, *args, **kwargs):
+    _original_init(self, *args, **kwargs)
+    instances = _active_instances.get()
+    if instances is not None:
+        instances.append(weakref.ref(self))
+
+
+Datasette.__init__ = _tracking_init
+
+
+def pytest_addoption(parser):
+    parser.addini(
+        "datasette_autoclose",
+        help=(
+            "Automatically close Datasette instances created inside test "
+            "bodies (default: true)."
+        ),
+        default="true",
+    )
+
+
+def _enabled(config) -> bool:
+    value = config.getini("datasette_autoclose")
+    if isinstance(value, bool):
+        return value
+    return str(value).strip().lower() not in ("false", "0", "no", "off")
+
+
+@pytest.hookimpl(hookwrapper=True)
+def pytest_runtest_call(item):
+    if not _enabled(item.config):
+        yield
+        return
+    refs: list[weakref.ref] = []
+    token = _active_instances.set(refs)
+    try:
+        yield
+    finally:
+        _active_instances.reset(token)
+        for ref in reversed(refs):
+            ds = ref()
+            if ds is None:
+                continue
+            try:
+                ds.close()
+            except Exception as e:
+                item.warn(
+                    pytest.PytestUnraisableExceptionWarning(
+                        f"Error closing Datasette instance: {e!r}"
+                    )
+                )