Crash with no text in layout and very small widths

[DJMcNab]

To reproduce, you can apply this patch then select all and press backspace or delete:

Patch to reproduce

diff --git a/examples/vello_editor/src/main.rs b/examples/vello_editor/src/main.rs
index 0422e76..8ab97cf 100644
--- a/examples/vello_editor/src/main.rs
+++ b/examples/vello_editor/src/main.rs
@@ -119,7 +119,7 @@ impl ApplicationHandler<accesskit_winit::Event> for SimpleVelloApp<'_> {
 
         self.editor.transact(|txn| {
             txn.set_scale(1.0);
-            txn.set_width(Some(size.width as f32 - 2f32 * text::INSET));
+            txn.set_width(Some(0.0)); // This can be a higher value and still reproduce
             txn.set_text(text::LOREM);
         });
 
@@ -238,9 +238,8 @@ impl ApplicationHandler<accesskit_winit::Event> for SimpleVelloApp<'_> {
                     .resize_surface(&mut render_state.surface, size.width, size.height);
                 self.editor.transact(|txn| {
                     txn.set_scale(1.0);
-                    txn.set_width(Some(size.width as f32 - 2f32 * text::INSET));
                     txn.set_default_style(Arc::new([
-                        StyleProperty::FontSize(32.0),
+                        StyleProperty::FontSize(16.0),
                         StyleProperty::LineHeight(1.2),
                         GenericFamily::SystemUi.into(),
                     ]));
diff --git a/examples/vello_editor/src/text.rs b/examples/vello_editor/src/text.rs
index 2211c7e..178b033 100644
--- a/examples/vello_editor/src/text.rs
+++ b/examples/vello_editor/src/text.rs
@@ -77,7 +77,7 @@ impl Editor {
     pub fn handle_event(&mut self, event: WindowEvent) {
         match event {
             WindowEvent::Resized(size) => {
-                self.transact(|txn| txn.set_width(Some(size.width as f32 - 2f32 * INSET)));
+                // self.transact(|txn| txn.set_width(Some(1.0)));
             }
             WindowEvent::ModifiersChanged(modifiers) => {
                 self.modifiers = Some(modifiers);

On my machine, any width less than an unknown value in [3.52, 3.521) causes a crash. The backtrace is:

Backtrace

thread 'main' panicked at parley/parley/src/layout/line/greedy.rs:740:26:
called `Option::unwrap()` on a `None` value
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: core::option::unwrap_failed
   4: parley::layout::line::greedy::try_commit_line
   5: parley::layout::line::greedy::BreakLines<B>::break_remaining
   6: parley::layout::editor::PlainEditor<T>::update_layout
   7: parley::layout::editor::PlainEditor<T>::replace_selection
   8: parley::layout::editor::PlainEditor<T>::transact
   9: vello_editor::text::Editor::handle_event
  10: <vello_editor::SimpleVelloApp as winit::application::ApplicationHandler<accesskit_winit::Event>>::window_event
  11: core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut
  12: winit::platform_impl::linux::wayland::event_loop::EventLoop<T>::pump_events
  13: winit::platform_impl::linux::wayland::event_loop::EventLoop<T>::run_on_demand
  14: vello_editor::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

And therefore the offending unwrap is:

parley/parley/src/layout/line/greedy.rs

Lines 765 to 767 in c0d158b

	let first_cluster = run
	.get(cluster_range.start - run_data.cluster_range.start)
	.unwrap();

[nicoburns]

The following patch fixes the crash for me, but causes the cursor position in an empty layout to display as if there was a line-break (it's on the "second line"):

diff --git a/parley/src/layout/line/greedy.rs b/parley/src/layout/line/greedy.rs
index 967df61..1c8e89e 100644
--- a/parley/src/layout/line/greedy.rs
+++ b/parley/src/layout/line/greedy.rs
@@ -759,7 +759,7 @@ fn try_commit_line<B: Brush>(

                 // Push run to line
                 let run = Run::new(layout, 0, 0, run_data, None);
-                let text_range = if run_data.cluster_range.is_empty() {
+                let text_range = if cluster_range.is_empty() {
                     0..0
                 } else {
                     let first_cluster = run

[nicoburns]

The LayoutData (post-shaping) seems to get itself into a pretty weird state after shaping the "dummy space" for empty text. There is an item, run, and cluster. But text_len is 0, and there are no glyphs:

[parley/src/layout/line/greedy.rs:760:17] &layout.data.text_len = 0
[parley/src/layout/line/greedy.rs:761:17] &layout.data.items = [
    LayoutItem {
        kind: TextRun,
        index: 0,
        bidi_level: 0,
    },
]
[parley/src/layout/line/greedy.rs:762:17] &layout.data.runs = [
    RunData {
        text_range: 0..1,
        glyph_start: 0,
    },
]
[parley/src/layout/line/greedy.rs:763:17] &layout.data.glyphs = []
[parley/src/layout/line/greedy.rs:764:17] &layout.data.clusters = [
    ClusterData {
        info:   sw,
        flags: 0,
        style_index: 0,
        glyph_len: 255,
        text_len: 1,
        glyph_offset: 3,
        text_offset: 0,
        advance: 6.5625,
    },
]