Registering an Action Handler
You can register actions for a Search Provider. Users can access registered actions via the More Options (⋮) icon in the search results.
Note
Registering an action handler and registering a Search Provider are different processes. You can register new action handlers for existing Search Providers.
To register an action, you create a function tagged with the [SearchActionsProvider] attribute. This function must return an IEnumerable<SearchAction>.
The following example shows how to register actions for the Asset Search Provider.
[SearchActionsProvider]
internal static IEnumerable<SearchAction> ActionHandlers()
{
    return new[]
    {
        new SearchAction("asset", "select", Icons.@goto, "Select asset...")
        {
            handler = (item, context) =>
            {
                var asset = AssetDatabase.LoadAssetAtPath<Object>(item.id);
                if (asset != null)
                {
                    Selection.activeObject = asset;
                    EditorGUIUtility.PingObject(asset);
                    EditorWindow.FocusWindowIfItsOpen(
                        Utils.GetProjectBrowserWindowType());
                }
            }
        },
        new SearchAction("asset", "open", SearchIcon.open, "Open asset... (Alt+Enter)")
        {
            handler = (item, context) =>
            {
                var asset = AssetDatabase.LoadAssetAtPath<Object>(item.id);
                if (asset != null)
                    AssetDatabase.OpenAsset(asset);
            }
        },
        new SearchAction("asset", "reveal", SearchIcon.folder, "Show in Explorer")
        {
            handler = (item, context) =>
            {
                EditorUtility.RevealInFinder(item.id);
            }
        }
    };
}
Search actions
The SearchAction class describes an action and provides a handler to execute the action on a specific SearchItem.
public class SearchAction
{
    public SearchAction(string providerType, string name,
                        Texture2D icon = null,
                        string tooltip = null);
    public ActionHandler handler;
    public EnabledHandler isEnabled;
}
The providerType is the unique ID of the provider that you register the action for.
The ActionHandler has the following signature:
// item: item that needs the action to be executed.
// context: search context of the SearchTool when the item is executed.
public delegate void ActionHandler(SearchItem item, SearchContext context);
You can set up an action with the isEnabled predicate, which determines whether an action is available for a specific item.
Contextual search actions
To provide contextual (right-click) actions for specific types of items in search results, register an action named context for the Search Provider.
The following example is from the Asset Search Provider:
new SearchAction(type, "context", null, "Context")
{
    handler = (item, context) =>
    {
        var asset = AssetDatabase.LoadAssetAtPath<Object>(item.id);
        if (asset != null)
        {
            Selection.activeObject = asset;
            EditorUtility.DisplayPopupMenu(
                QuickSearchTool.ContextualActionPosition,
                "Assets/", null);
        }
    }
}