Expose the is_required property

[DataTriny]

This property is also used on Windows to indicate that an item must be selected from a listbox. This will come in a future PR.

Directly merging the two commits should properly update the version of the affected crates.

Tested with the following test program:

Test program source code

use accesskit::{Action, Node, NodeId, Rect, Role, Tree, TreeUpdate};
use accesskit_winit::{Adapter, Event as AccessKitEvent, WindowEvent as AccessKitWindowEvent};
use std::error::Error;
use winit::{
    application::ApplicationHandler,
    event::WindowEvent,
    event_loop::{ActiveEventLoop, EventLoop, EventLoopProxy},
    window::{Window, WindowId},
};

const WINDOW_TITLE: &str = "Test App";

const WINDOW_ID: NodeId = NodeId(0);
const TEXT_INPUT_ID: NodeId = NodeId(1);
const INITIAL_FOCUS: NodeId = TEXT_INPUT_ID;

const TEXT_INPUT_RECT: Rect = Rect {
    x0: 20.0,
    y0: 20.0,
    x1: 200.0,
    y1: 60.0,
};

fn build_text_input(label: &str) -> Node {
    let mut node = Node::new(Role::TextInput);
    node.set_bounds(TEXT_INPUT_RECT);
    node.set_label(label);
    node.set_required();
    node.add_action(Action::Focus);
    node
}

struct UiState {
    focus: NodeId,
}

impl UiState {
    fn new() -> Self {
        Self {
            focus: INITIAL_FOCUS,
        }
    }

    fn build_root(&mut self) -> Node {
        let mut node = Node::new(Role::Window);
        node.set_children(vec![TEXT_INPUT_ID]);
        node.set_label(WINDOW_TITLE);
        node
    }

    fn build_initial_tree(&mut self) -> TreeUpdate {
        let root = self.build_root();
        let text_input = build_text_input("Your name");
        let tree = Tree::new(WINDOW_ID);
        TreeUpdate {
            nodes: vec![(WINDOW_ID, root), (TEXT_INPUT_ID, text_input)],
            tree: Some(tree),
            focus: self.focus,
        }
    }
}

struct WindowState {
    window: Window,
    adapter: Adapter,
    ui: UiState,
}

impl WindowState {
    fn new(window: Window, adapter: Adapter, ui: UiState) -> Self {
        Self {
            window,
            adapter,
            ui,
        }
    }
}

struct Application {
    event_loop_proxy: EventLoopProxy<AccessKitEvent>,
    window: Option<WindowState>,
}

impl Application {
    fn new(event_loop_proxy: EventLoopProxy<AccessKitEvent>) -> Self {
        Self {
            event_loop_proxy,
            window: None,
        }
    }

    fn create_window(&mut self, event_loop: &ActiveEventLoop) -> Result<(), Box<dyn Error>> {
        let window_attributes = Window::default_attributes()
            .with_title(WINDOW_TITLE)
            .with_visible(false);

        let window = event_loop.create_window(window_attributes)?;
        let adapter = Adapter::with_event_loop_proxy(&window, self.event_loop_proxy.clone());
        window.set_visible(true);

        self.window = Some(WindowState::new(window, adapter, UiState::new()));
        Ok(())
    }
}

impl ApplicationHandler<AccessKitEvent> for Application {
    fn window_event(&mut self, _: &ActiveEventLoop, _: WindowId, event: WindowEvent) {
        let window = match &mut self.window {
            Some(window) => window,
            None => return,
        };
        let adapter = &mut window.adapter;

        adapter.process_event(&window.window, &event);
        match event {
            WindowEvent::CloseRequested => {
                self.window = None;
            }
            _ => (),
        }
    }

    fn user_event(&mut self, _: &ActiveEventLoop, user_event: AccessKitEvent) {
        let window = match &mut self.window {
            Some(window) => window,
            None => return,
        };
        let adapter = &mut window.adapter;
        let state = &mut window.ui;

        match user_event.window_event {
            AccessKitWindowEvent::InitialTreeRequested => {
                adapter.update_if_active(|| state.build_initial_tree());
            }
            _ => (),
        }
    }

    fn resumed(&mut self, event_loop: &ActiveEventLoop) {
        self.create_window(event_loop)
            .expect("failed to create initial window");
    }

    fn about_to_wait(&mut self, event_loop: &ActiveEventLoop) {
        if self.window.is_none() {
            event_loop.exit();
        }
    }
}

fn main() -> Result<(), Box<dyn Error>> {
    let event_loop = EventLoop::with_user_event().build()?;
    let mut state = Application::new(event_loop.create_proxy());
    event_loop.run_app(&mut state).map_err(Into::into)
}