addPlugin method

@override AppBuilder addPlugin(Plugin plugin)

Builds plugin into this app if it has not already been added.

Implementation

@override
AppBuilder addPlugin(Plugin plugin) {
  _assertOpen();
  final type = plugin.runtimeType;
  final existing = _addedPlugins[type];
  if (existing != null) {
    // Allow only the same instance twice.
    if (identical(existing, plugin)) return this;
    throw StateError(
      'A $type has already been added. Adding a second, different instance '
      'would be silently ignored along with its configuration; add each '
      'plugin exactly once.',
    );
  }
  for (final dependency in plugin.dependencies) {
    if (!_addedPlugins.containsKey(dependency)) {
      throw StateError(
        'Plugin $type requires $dependency, which has not been added. '
        'Add $dependency before $type.',
      );
    }
  }
  _addedPlugins[type] = plugin;
  plugin.build(this);
  return this;
}