specialized_mesh_pipeline example panics when hovering over mesh

[rparrett]

Bevy version

main
bisected to #15800.

Relevant system information

SystemInfo { os: "MacOS 14.5 ", kernel: "23.5.0", cpu: "Apple M1 Max", core_count: "10", memory: "64.0 GiB" }
AdapterInfo { name: "Apple M1 Max", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }

What you did

• cargo run --example specialized_mesh_pipeline
• hover over over the triangles

What went wrong

thread 'Compute Task Pool (3)' panicked at crates/bevy_picking/src/mesh_picking/ray_cast/intersections.rs:145:29:
index out of bounds: the len is 3 but the index is 3
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Encountered a panic in system `bevy_picking::mesh_picking::update_hits`!
Encountered a panic in system `bevy_app::main_schedule::Main::run_main`!

[alice-i-cecile]

I'm pretty sure something is malformed in the mesh. This looks like the exact issue spotted by @tbillington and called out as not a problem in #15800 (comment) by @Jondolf.

[rparrett]

It looks like it is because the mesh doesn't have normals. Don't feel like we should be packing there, but it seems like there's a pretty nasty perf hit to write non-packing code based on the discussion linked above.