gh-105539: Emit ResourceWarning if sqlite3 database is not closed explicitly (#108015)

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

@@ -158,6 +158,13 @@ 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`.)
+
 tkinter
 -------
 

Lib/test/test_sqlite3/test_dbapi.py

@@ -583,6 +583,12 @@ class ConnectionTests(unittest.TestCase):
             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

@@ -493,6 +493,14 @@ connection_finalize(PyObject *self)
     }
 
     /* Clean up if user has not called .close() explicitly. */
+    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);
+            }
+        }
+    }
     if (connection_close(con) < 0) {
         if (teardown) {
             PyErr_Clear();