Error Boundaries

Catch panics in child views and render a fallback instead of crashing.

View::error_boundary()
    .child(risky_view)
    .fallback(View::text("Something went wrong"))
    .build()

Run with: cargo run -p telex-tui --example 37_error_boundary

What are error boundaries?

Error boundaries wrap a child view tree and catch any panics that occur during rendering. Instead of crashing the entire application, the boundary renders a fallback view.

This is useful for:

Isolating untrusted or experimental UI sections
Graceful degradation when data is unexpected
Preventing one broken widget from taking down the whole app

Builder API

View::error_boundary()
    .child(view)        // the view that might panic
    .fallback(view)     // shown if child panics
    .build()

If no fallback is provided, the default is View::text("[error boundary: child panicked]").

Example: safe data display

let data = state!(cx, || None::<UserProfile>);

View::error_boundary()
    .child({
        let profile = data.get().unwrap();  // might panic if None
        View::text(format!("Welcome, {}!", profile.name))
    })
    .fallback(View::text("Profile unavailable"))
    .build()

Example: isolating widgets

View::vstack()
    .child(View::text("Header — always visible"))
    .child(
        View::error_boundary()
            .child(possibly_broken_widget())
            .fallback(
                View::styled_text("Widget failed to render")
                    .color(Color::Red)
                    .build()
            )
            .build()
    )
    .child(View::text("Footer — always visible"))
    .build()

What gets caught

Error boundaries catch panics during child view rendering. This includes:

unwrap() on None or Err
panic!() calls
Index out of bounds
Any other panic in the child view tree

Error boundaries do not catch:

Panics in effect cleanup functions
Panics in other threads (those abort the process)
Logic errors that don't panic

Tips

Keep fallbacks simple — The fallback should be a static view that can't itself panic.

Nest boundaries — You can nest error boundaries to isolate different parts of your UI independently.

Don't overuse — Error boundaries are for genuinely risky rendering. If you can validate data before rendering, prefer that.

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