bpo-42064: Migrate to `sqlite3_create_collation_v2` (GH-27156)

This implies that SQLite now takes care of destroying the callback
context (the PyObject callable it has been passed), so we can strip the
collation dict from the connection object.

Modules/_sqlite/connection.c

@@ -177,11 +177,6 @@ pysqlite_connection_init_impl(pysqlite_Connection *self,
     self->function_pinboard_progress_handler = NULL;
     self->function_pinboard_authorizer_cb = NULL;
 
-    Py_XSETREF(self->collations, PyDict_New());
-    if (!self->collations) {
-        return -1;
-    }
-
     pysqlite_state *state = pysqlite_get_state(NULL);
     self->Warning               = state->Warning;
     self->Error                 = state->Error;
@@ -249,7 +244,6 @@ connection_traverse(pysqlite_Connection *self, visitproc visit, void *arg)
     Py_VISIT(self->function_pinboard_trace_callback);
     Py_VISIT(self->function_pinboard_progress_handler);
     Py_VISIT(self->function_pinboard_authorizer_cb);
-    Py_VISIT(self->collations);
     return 0;
 }
 
@@ -265,7 +259,6 @@ connection_clear(pysqlite_Connection *self)
     Py_CLEAR(self->function_pinboard_trace_callback);
     Py_CLEAR(self->function_pinboard_progress_handler);
     Py_CLEAR(self->function_pinboard_authorizer_cb);
-    Py_CLEAR(self->collations);
     return 0;
 }
 
@@ -1780,29 +1773,29 @@ pysqlite_connection_create_collation_impl(pysqlite_Connection *self,
     if (!uppercase_name_str)
         goto finally;
 
-    if (callable != Py_None && !PyCallable_Check(callable)) {
-        PyErr_SetString(PyExc_TypeError, "parameter must be callable");
-        goto finally;
+    int flags = SQLITE_UTF8;
+    if (callable == Py_None) {
+        rc = sqlite3_create_collation_v2(self->db, uppercase_name_str, flags,
+                                         NULL, NULL, NULL);
     }
-
-    if (callable != Py_None) {
-        if (PyDict_SetItem(self->collations, uppercase_name, callable) == -1)
-            goto finally;
-    } else {
-        if (PyDict_DelItem(self->collations, uppercase_name) == -1)
+    else {
+        if (!PyCallable_Check(callable)) {
+            PyErr_SetString(PyExc_TypeError, "parameter must be callable");
             goto finally;
+        }
+        rc = sqlite3_create_collation_v2(self->db, uppercase_name_str, flags,
+                                         Py_NewRef(callable),
+                                         &pysqlite_collation_callback,
+                                         &_destructor);
     }
 
-    rc = sqlite3_create_collation(self->db,
-                                  uppercase_name_str,
-                                  SQLITE_UTF8,
-                                  (callable != Py_None) ? callable : NULL,
-                                  (callable != Py_None) ? pysqlite_collation_callback : NULL);
     if (rc != SQLITE_OK) {
+        /* Unlike other sqlite3_* functions, the destructor callback is _not_
+         * called if sqlite3_create_collation_v2() fails, so we have to free
+         * the context before returning.
+         */
         if (callable != Py_None) {
-            if (PyDict_DelItem(self->collations, uppercase_name) < 0) {
-                PyErr_Clear();
-            }
+            Py_DECREF(callable);
         }
         _pysqlite_seterror(self->db);
         goto finally;

Modules/_sqlite/connection.h

@@ -82,9 +82,6 @@ typedef struct
     PyObject* function_pinboard_progress_handler;
     PyObject* function_pinboard_authorizer_cb;
 
-    /* a dictionary of registered collation name => collation callable mappings */
-    PyObject* collations;
-
     /* Exception objects: borrowed refs. */
     PyObject* Warning;
     PyObject* Error;