ext/pdo: Fix GC freeing callbacks of a shared persistent connection

NEWS

@@ -89,6 +89,9 @@ PHP                                                                        NEWS
     (Ilia Alshanetsky)
   . Fixed a duplicate warning when ATTR_STATEMENT_CLASS is rejected on a
     persistent connection. (Ilia Alshanetsky)
+  . Fixed crash when the garbage collector freed SQLite user functions,
+    aggregates, or collations of a persistent connection shared by several
+    PDO objects. (Ilia Alshanetsky)
 
 - Phpdbg:
   . Fix wrong command names. (ndossche, Weilin Du)

ext/pdo/pdo_dbh.c

@@ -1443,7 +1443,8 @@ static HashTable *dbh_get_gc(zend_object *object, zval **gc_data, int *gc_count)
 	pdo_dbh_t *dbh = php_pdo_dbh_fetch_inner(object);
 	zend_get_gc_buffer *gc_buffer = zend_get_gc_buffer_create();
 	zend_get_gc_buffer_add_zval(gc_buffer, &dbh->def_stmt_ctor_args);
-	if (dbh->methods && dbh->methods->get_gc) {
+	if (dbh->methods && dbh->methods->get_gc
+			&& (!dbh->is_persistent || dbh->refcount <= 2)) {
 		dbh->methods->get_gc(dbh, gc_buffer);
 	}
 	zend_get_gc_buffer_use(gc_buffer, gc_data, gc_count);

ext/pdo_sqlite/tests/gc_persistent_shared.phpt

@@ -0,0 +1,30 @@
+--TEST--
+GC must not free callbacks of a persistent connection shared by several PDO objects
+--EXTENSIONS--
+pdo_sqlite
+--FILE--
+<?php
+class Repo {
+    public Pdo\Sqlite $pdo;
+
+    public function __construct(public string $name) {
+        $this->pdo = Pdo\Sqlite::connect('sqlite::memory:', null, null, [PDO::ATTR_PERSISTENT => true]);
+        $this->pdo->createFunction("udf_$name", [$this, 'udf'], 1);
+    }
+
+    public function udf($x) {
+        return $this->name . $x;
+    }
+}
+
+$repos = [new Repo('one'), new Repo('two')];
+echo "collected: "; var_dump(gc_collect_cycles());
+echo "udf_one: "; var_dump($repos[0]->pdo->query("SELECT udf_one('!')")->fetchColumn());
+echo "udf_two: "; var_dump($repos[1]->pdo->query("SELECT udf_two('?')")->fetchColumn());
+
+unset($repos[0]->pdo, $repos[1]->pdo);
+?>
+--EXPECT--
+collected: int(0)
+udf_one: string(4) "one!"
+udf_two: string(4) "two?"