ratatui/examples/panic.rs

//! # [Ratatui] Panic Hook example
//!
//! The latest version of this example is available in the [examples] folder in the repository.
//!
//! Please note that the examples are designed to be run against the `main` branch of the Github
//! repository. This means that you may not be able to compile with the latest release version on
//! crates.io, or the one that you have installed locally.
//!
//! See the [examples readme] for more information on finding examples that match the version of the
//! library you are using.
//!
//! [Ratatui]: https://github.com/ratatui/ratatui
//! [examples]: https://github.com/ratatui/ratatui/blob/main/examples
//! [examples readme]: https://github.com/ratatui/ratatui/blob/main/examples/README.md
//!
//! Prior to Ratatui 0.28.1, a panic hook had to be manually set up to ensure that the terminal was
//! reset when a panic occurred. This was necessary because a panic would interrupt the normal
//! control flow and leave the terminal in a distorted state.
//!
//! Starting with Ratatui 0.28.1, the panic hook is automatically set up by the new `ratatui::init`
//! function, so you no longer need to manually set up the panic hook. This example now demonstrates
//! how the panic hook acts when it is enabled by default.
//!
//! When exiting normally or when handling `Result::Err`, we can reset the terminal manually at the
//! end of `main` just before we print the error.
//!
//! Because a panic interrupts the normal control flow, manually resetting the terminal at the end
//! of `main` won't do us any good. Instead, we need to make sure to set up a panic hook that first
//! resets the terminal before handling the panic. This both reuses the standard panic hook to
//! ensure a consistent panic handling UX and properly resets the terminal to not distort the
//! output.
//!
//! That's why this example is set up to show both situations, with and without the panic hook, to
//! see the difference.
//!
//! For more information on how to set this up manually, see the [Color Eyre recipe] in the Ratatui
//! website.
//!
//! [Color Eyre recipe]: https://ratatui.rs/recipes/apps/color-eyre

use color_eyre::{eyre::bail, Result};
use ratatui::{
    crossterm::event::{self, Event, KeyCode},
    text::Line,
    widgets::{Block, Paragraph},
    DefaultTerminal, Frame,
};

fn main() -> Result<()> {
    color_eyre::install()?;
    let terminal = ratatui::init();
    let app_result = App::new().run(terminal);
    ratatui::restore();
    app_result
}
struct App {
    hook_enabled: bool,
}

impl App {
    const fn new() -> Self {
        Self { hook_enabled: true }
    }

    fn run(mut self, mut terminal: DefaultTerminal) -> Result<()> {
        loop {
            terminal.draw(|frame| self.draw(frame))?;

            if let Event::Key(key) = event::read()? {
                match key.code {
                    KeyCode::Char('p') => panic!("intentional demo panic"),
                    KeyCode::Char('e') => bail!("intentional demo error"),
                    KeyCode::Char('h') => {
                        let _ = std::panic::take_hook();
                        self.hook_enabled = false;
                    }
                    KeyCode::Char('q') => return Ok(()),
                    _ => {}
                }
            }
        }
    }

    fn draw(&self, frame: &mut Frame) {
        let text = vec![
            if self.hook_enabled {
                Line::from("HOOK IS CURRENTLY **ENABLED**")
            } else {
                Line::from("HOOK IS CURRENTLY **DISABLED**")
            },
            Line::from(""),
            Line::from("Press `p` to cause a panic"),
            Line::from("Press `e` to cause an error"),
            Line::from("Press `h` to disable the panic hook"),
            Line::from("Press `q` to quit"),
            Line::from(""),
            Line::from("When your app panics without a panic hook, you will likely have to"),
            Line::from("reset your terminal afterwards with the `reset` command"),
            Line::from(""),
            Line::from("Try first with the panic handler enabled, and then with it disabled"),
            Line::from("to see the difference"),
        ];

        let paragraph = Paragraph::new(text)
            .block(Block::bordered().title("Panic Handler Demo"))
            .centered();

        frame.render_widget(paragraph, frame.area());
    }
}