gh-105539: Emit ResourceWarning if sqlite3 database is not closed explicitly

Doc/library/sqlite3.rst

@@ -630,6 +630,12 @@ Connection objects
       * :ref:`sqlite3-connection-shortcuts`
       * :ref:`sqlite3-connection-context-manager`
 
+
+   .. versionchanged:: 3.13
+
+      A :exc:`ResourceWarning` is emitted if :meth:`close` is not called before
+      a :class:`!Connection` object is deleted.
+
    An SQLite database connection has the following attributes and methods:
 
    .. method:: cursor(factory=Cursor)

Doc/whatsnew/3.13.rst

@@ -144,6 +144,13 @@ pathlib
   :meth:`~pathlib.Path.is_dir`.
   (Contributed by Barney Gale in :gh:`77609` and :gh:`105793`.)
 
+sqlite3
+-------
+
+* A :exc:`ResourceWarning` is now emitted if a :class:`sqlite3.Connection`
+  object is not :meth:`closed <sqlite3.Connection.close>` explicitly.
+  (Contributed by Erlend E. Aasland in :gh:`105539`.)
+
 traceback
 ---------
 

Lib/test/test_sqlite3/test_dbapi.py

@@ -583,6 +583,12 @@ def test_connect_positional_arguments(self):
             cx.close()
         self.assertEqual(cm.filename, __file__)
 
+    def test_connection_resource_warning(self):
+        with self.assertWarns(ResourceWarning):
+            cx = sqlite.connect(":memory:")
+            del cx
+            gc_collect()
+
 
 class UninitialisedConnectionTests(unittest.TestCase):
     def setUp(self):

Misc/NEWS.d/next/Library/2023-08-16-14-30-13.gh-issue-105539.29lA6c.rst

@@ -0,0 +1,3 @@
+:mod:`sqlite3` now emits an :exc:`ResourceWarning` if a
+:class:`sqlite3.Connection` object is not :meth:`closed
+<sqlite3.connection.close>` explicitly. Patch by Erlend E. Aasland.

Modules/_sqlite/connection.c

@@ -249,7 +249,9 @@ pysqlite_connection_init_impl(pysqlite_Connection *self, PyObject *database,
     if (self->initialized) {
         PyTypeObject *tp = Py_TYPE(self);
         tp->tp_clear((PyObject *)self);
-        connection_close(self);
+        if (self->db) {
+            connection_close(self);
+        }
         self->initialized = 0;
     }
 
@@ -440,40 +442,61 @@ remove_callbacks(sqlite3 *db)
 static void
 connection_close(pysqlite_Connection *self)
 {
-    if (self->db) {
-        if (self->autocommit == AUTOCOMMIT_DISABLED &&
-            !sqlite3_get_autocommit(self->db))
-        {
-            /* If close is implicitly called as a result of interpreter
-             * tear-down, we must not call back into Python. */
-            if (_Py_IsInterpreterFinalizing(PyInterpreterState_Get())) {
-                remove_callbacks(self->db);
-            }
-            (void)connection_exec_stmt(self, "ROLLBACK");
-        }
+    assert(self->db);
+    if (self->autocommit == AUTOCOMMIT_DISABLED &&
+        !sqlite3_get_autocommit(self->db))
+    {
+        (void)connection_exec_stmt(self, "ROLLBACK");
+    }
 
-        free_callback_contexts(self);
+    free_callback_contexts(self);
 
-        sqlite3 *db = self->db;
-        self->db = NULL;
+    sqlite3 *db = self->db;
+    self->db = NULL;
 
-        Py_BEGIN_ALLOW_THREADS
-        int rc = sqlite3_close_v2(db);
-        assert(rc == SQLITE_OK), (void)rc;
-        Py_END_ALLOW_THREADS
-    }
+    Py_BEGIN_ALLOW_THREADS
+    int rc = sqlite3_close_v2(db);
+    assert(rc == SQLITE_OK), (void)rc;
+    Py_END_ALLOW_THREADS
 }
 
 static void
-connection_dealloc(pysqlite_Connection *self)
+connection_finalize(PyObject *self)
 {
-    PyTypeObject *tp = Py_TYPE(self);
-    PyObject_GC_UnTrack(self);
-    tp->tp_clear((PyObject *)self);
+    pysqlite_Connection *con = (pysqlite_Connection *)self;
+    PyObject *exc = PyErr_GetRaisedException();
+
+    /*
+     * Before implicitly closing, make sure we're not accidentally part
+     * of the interpreter tear-down; in that case, we must not call back
+     * into Python code.
+     */
+    if (_Py_IsInterpreterFinalizing(PyInterpreterState_Get())) {
+        remove_callbacks(con->db);
+    }
 
     /* Clean up if user has not called .close() explicitly. */
-    connection_close(self);
+    if (con->db) {
+        if (PyErr_ResourceWarning(self, 1, "unclosed database in %R", self)) {
+            /* Spurious errors can appear at shutdown */
+            if (PyErr_ExceptionMatches(PyExc_Warning)) {
+                PyErr_WriteUnraisable(self);
+            }
+        }
+        connection_close(con);
+    }
+    PyErr_SetRaisedException(exc);
+}
 
+static void
+connection_dealloc(PyObject *self)
+{
+    if (PyObject_CallFinalizerFromDealloc(self) < 0) {
+        return;
+    }
+    PyTypeObject *tp = Py_TYPE(self);
+    PyObject_GC_UnTrack(self);
+    tp->tp_clear(self);
     tp->tp_free(self);
     Py_DECREF(tp);
 }
@@ -621,7 +644,9 @@ pysqlite_connection_close_impl(pysqlite_Connection *self)
 
     pysqlite_close_all_blobs(self);
     Py_CLEAR(self->statement_cache);
-    connection_close(self);
+    if (self->db) {
+        connection_close(self);
+    }
 
     Py_RETURN_NONE;
 }
@@ -2555,6 +2580,7 @@ static struct PyMemberDef connection_members[] =
 };
 
 static PyType_Slot connection_slots[] = {
+    {Py_tp_finalize, connection_finalize},
     {Py_tp_dealloc, connection_dealloc},
     {Py_tp_doc, (void *)connection_doc},
     {Py_tp_methods, connection_methods},