Derive Macro AppContext 

#[derive(AppContext)]
{
    // Attributes available to this derive:
    #[app]
}

#[derive(AppContext)] is used to create a context out of anything that holds a &mut App Note that a #[app] attribute is required to identify the variable holding the &mut App.

Failure to add the attribute causes a compile error:

#[derive(AppContext)]
struct MyContext<'a> {
    app: &'a mut gpui::App
}