tui: add ErrorBoundary component

tui/src/tui_content/tui_error.rs

@@ -0,0 +1,24 @@
+use crate::*;
+use ratatui::style::Stylize;
+
+// Thunks can be natural error boundaries!
+pub struct ErrorBoundary<O: Output, T: Content<O>>(std::marker::PhantomData<O>, Perhaps<T>);
+
+impl<O: Output, T: Content<O>> ErrorBoundary<O, T> {
+    pub fn new (content: Perhaps<T>) -> Self {
+        Self(Default::default(), content)
+    }
+}
+
+impl<T: Content<TuiOut>> Content<TuiOut> for ErrorBoundary<TuiOut, T> {
+    fn content (&self) -> impl Render<TuiOut> + '_ {
+        ThunkRender::new(|to|match self.1.as_ref() {
+            Ok(Some(content)) => content.render(to),
+            Ok(None) => to.blit(&"empty?", 0, 0, Some(Style::default().yellow())),
+            Err(e) => Content::render(&Tui::fg_bg(
+                Color::Rgb(255,224,244), Color::Rgb(96,24,24), Bsp::s(
+                    Bsp::e(Tui::bold(true, "oops. "), "rendering failed."),
+                    Bsp::e("\"why?\" ", Tui::bold(true, &format!("{e}"))))), to)
+        })
+    }
+}