SelectionHelpers

ComponentExists Selected GameObjects contain a component type.

void OnDrawGizmos() {
    if (SelectionHelpers.ComponentExists<IDebug>()) {
        // Draw Gizmos if a "IDebug" component is selected
    }
}

Contains Selected GameObjects contain a GameObject or MonoBehaviour

void OnDrawGizmos() {
    if (SelectionHelpers.Contains(MyComponent)) {
        // Draw Gizmos if "MyComponent" is selected
    }
}