Handle custom database drivers (#6127)

* Handle custom database drivers.

* More graceful handling of cascading database driver discovery

* Fix CS

* Fix phpstan-discovered error in logic

---------

Co-authored-by: Moshe Weitzman <[email protected]>

src/Sql/SqlBase.php

@@ -119,14 +119,29 @@ public static function create(array $options = []): ?SqlBase
     public static function getInstance($db_spec, $options): ?self
     {
         $driver = $db_spec['driver'];
+        // Drush ships drivers for core database types, and modules/libraries
+        // may define additional Drush DB drivers in this namespace.
         $class_name = !empty($driver) ? 'Drush\Sql\Sql' . ucfirst($driver) : null;
-        if ($class_name && class_exists($class_name)) {
+        try {
+            if (!$class_name || !class_exists($class_name)) {
+                // Handle custom database drivers which extend a defined driver.
+                $driver_class = $db_spec['namespace'] . '\\Connection';
+                if (!class_exists($driver_class)) {
+                    throw new \InvalidArgumentException();
+                }
+                $connection = (new \ReflectionClass($driver_class))->newInstanceWithoutConstructor();
+                // This will only work if the method is basically static, as most
+                // will be...but we can't truly instantiate the Connection class
+                // here without also calling with a "real" PDO connection.
+                $class_name = 'Drush\Sql\Sql' . ucfirst($connection->databaseType());
+            }
             $instance = method_exists($class_name, 'make') ? $class_name::make($db_spec, $options) : new $class_name($db_spec, $options);
-            // Inject config
-            $instance->setConfig(Drush::config());
-            return $instance;
+        } catch (\Throwable) {
+            return null;
         }
-        return null;
+        // Inject config
+        $instance->setConfig(Drush::config());
+        return $instance;
     }
 
     /*