gh-94321: Document sqlite3.PrepareProtocol (GH-94620)

(cherry picked from commit fb6dccae)

Co-authored-by: Erlend Egeberg Aasland <erlend.aasland@protonmail.com>

Doc/library/sqlite3.rst

@@ -1127,6 +1127,16 @@ Blob Objects
       end).
 
 
+PrepareProtocol Objects
+-----------------------
+
+.. class:: PrepareProtocol
+
+   The PrepareProtocol type's single purpose is to act as a :pep:`246` style
+   adaption protocol for objects that can :ref:`adapt themselves
+   <sqlite3-conform>` to :ref:`native SQLite types <sqlite3-types>`.
+
+
 .. _sqlite3-exceptions:
 
 Exceptions
@@ -1287,6 +1297,8 @@ As an application developer, it may make more sense to take direct control by
 registering custom adapter functions.
 
 
+.. _sqlite3-conform:
+
 Letting your object adapt itself
 """"""""""""""""""""""""""""""""
 

Misc/NEWS.d/next/Documentation/2022-07-07-08-42-05.gh-issue-94321.pmCIPb.rst

+Document the :pep:`246` style protocol type
+:class:`sqlite3.PrepareProtocol`.

Modules/_sqlite/prepare_protocol.c

@@ -46,10 +46,13 @@ pysqlite_prepare_protocol_dealloc(pysqlite_PrepareProtocol *self)
     Py_DECREF(tp);
 }
 
+PyDoc_STRVAR(doc, "PEP 246 style object adaption protocol type.");
+
 static PyType_Slot type_slots[] = {
     {Py_tp_dealloc, pysqlite_prepare_protocol_dealloc},
     {Py_tp_init, pysqlite_prepare_protocol_init},
     {Py_tp_traverse, pysqlite_prepare_protocol_traverse},
+    {Py_tp_doc, (void *)doc},
     {0, NULL},
 };