Segfault in create_render_pipeline when vertex shader returns void

[WorkForPizza]

Description
Trying to create a pipeline with a wgsl shader whose vertex function returns void results in a SIGSEGV and no error message.

Repro steps
Here's a small reproduction program

use winit::{
    event::{Event, WindowEvent},
    event_loop::{ControlFlow, EventLoop},
    window::WindowBuilder,
};
use pollster::FutureExt as _;

fn main() {
    let event_loop = EventLoop::new();
    let window = WindowBuilder::new().build(&event_loop).unwrap();

    let size = window.inner_size();

    let instance = wgpu::Instance::new(wgpu::InstanceDescriptor {
        backends: wgpu::Backends::all(),
        dx12_shader_compiler: Default::default(),
    });

    let surface = unsafe { instance.create_surface(&window) }.unwrap();

    let adapter = instance.request_adapter(
        &wgpu::RequestAdapterOptions {
            power_preference: wgpu::PowerPreference::default(),
            compatible_surface: Some(&surface),
            force_fallback_adapter: false,
        },
    ).block_on().unwrap();

    let (device, _queue) = adapter.request_device(
        &wgpu::DeviceDescriptor {
            features: wgpu::Features::empty(),
            limits: wgpu::Limits::downlevel_webgl2_defaults(),
            label: None,
        },
        None,
    ).block_on().unwrap();

    let surface_caps = surface.get_capabilities(&adapter);
    let surface_format = surface_caps.formats.iter()
        .copied()
        .filter(|f| f.describe().srgb)
        .next()
        .unwrap_or(surface_caps.formats[0]);
    let config = wgpu::SurfaceConfiguration {
        usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
        format: surface_format,
        width: size.width,
        height: size.height,
        present_mode: wgpu::PresentMode::Fifo,
        alpha_mode: wgpu::CompositeAlphaMode::Auto,
        view_formats: vec![],
    };
    surface.configure(&device, &config);

    let shader_src = r#"
    @vertex
    fn vs_main() {
        return;
    }

    @vertex
    fn vs_main2() -> @builtin(position) vec4<f32> {
        return vec4<f32>(0.0, 0.0, 0.0, 1.0);
    }

    @fragment
    fn fs_main() -> @location(0) vec4<f32> {
        return vec4<f32>(0.2, 0.2, 0.2, 1.0);
    }
"#;
    let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
        label: Some("Shader"),
        source: wgpu::ShaderSource::Wgsl(shader_src.into()),
    });
    let render_pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
        label: Some("Render Pipeline Layout"),
        bind_group_layouts: &[],
        push_constant_ranges: &[],
    });
    let _pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
        label: Some("Render Pipeline"),
        layout: Some(&render_pipeline_layout),
        vertex: wgpu::VertexState {
            module: &shader,
            entry_point: "vs_main",
            // entry_point: "vs_main2",
            buffers: &[],
        },
        fragment: Some(wgpu::FragmentState {
            module: &shader,
            entry_point: "fs_main",
            targets: &[Some(wgpu::ColorTargetState {
                format: config.format,
                blend: Some(wgpu::BlendState::REPLACE),
                write_mask: wgpu::ColorWrites::ALL,
            })],
        }),
        primitive: wgpu::PrimitiveState::default(),
        depth_stencil: None,
        multisample: wgpu::MultisampleState::default(),
        multiview: None,
    });

    event_loop.run(move |event, _, control_flow| {
        *control_flow = ControlFlow::Wait;

        match event {
            Event::WindowEvent {
                window_id,
                event: WindowEvent::CloseRequested,
            } if window_id == window.id() => *control_flow = ControlFlow::Exit,
            _ => (),
        }
    });
}

Expected vs observed behavior
Running the above program with cargo run will result in a segfault. Using "vs_main2" as the vertex entrypoint in the create_render_pipeline call will fix the issue and a window will appear. I see now that a wgsl vertex shader is required to return a position (https://www.w3.org/TR/WGSL/#function-restriction), however I still would've expected an error message instead of a fault.

You can see my output, as well as the backtrace below.

martin@M ~/r/wgpu-test2 (master)> cargo run
   Compiling wgpu-test2 v0.1.0 (/Users/martin/rust/wgpu-test2)
    Finished dev [unoptimized + debuginfo] target(s) in 0.44s
     Running `target/debug/wgpu-test2`
fish: Job 1, 'cargo run' terminated by signal SIGSEGV (Address boundary error)
martin@M ~/r/wgpu-test2 (master) [SIGSEGV]> lldb ./target/debug/wgpu-test2
(lldb) target create "./target/debug/wgpu-test2"
Current executable set to '/Users/martin/rust/wgpu-test2/target/debug/wgpu-test2' (arm64).
(lldb) r
Process 38529 launched: '/Users/martin/rust/wgpu-test2/target/debug/wgpu-test2' (arm64)
2023-03-01 22:25:57.869047-0600 wgpu-test2[38529:6359801] Compiler failed to build request
Process 38529 stopped
* thread #1, name = 'main', queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x3eadde6e3620)
    frame #0: 0x000000018bbdc278 libobjc.A.dylib`objc_release + 16
libobjc.A.dylib`objc_release:
->  0x18bbdc278 <+16>: ldr    x17, [x2, #0x20]
    0x18bbdc27c <+20>: tbz    w17, #0x2, 0x18bbdc2dc    ; <+116>
    0x18bbdc280 <+24>: tbz    w16, #0x0, 0x18bbdc2f8    ; <+144>
    0x18bbdc284 <+28>: lsr    x17, x16, #55
Target 0: (wgpu-test2) stopped.
(lldb) bt
* thread #1, name = 'main', queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x3eadde6e3620)
  * frame #0: 0x000000018bbdc278 libobjc.A.dylib`objc_release + 16
    frame #1: 0x000000018bbe4168 libobjc.A.dylib`AutoreleasePoolPage::releaseUntil(objc_object**) + 196
    frame #2: 0x000000018bbe0870 libobjc.A.dylib`objc_autoreleasePoolPop + 256
    frame #3: 0x000000010060f698 wgpu-test2`_$LT$objc..rc..autorelease..AutoReleaseHelper$u20$as$u20$core..ops..drop..Drop$GT$::drop::hdf6e7b1a4aa652e4(self=0x000000016fdf9650) at autorelease.rs:17:18
    frame #4: 0x000000010044b31c wgpu-test2`core::ptr::drop_in_place$LT$objc..rc..autorelease..AutoReleaseHelper$GT$::h00bb076898f42477((null)=0x000000016fdf9650) at mod.rs:490:1
    frame #5: 0x00000001003d82f4 wgpu-test2`objc::rc::autorelease::autoreleasepool::h51d955a4a1eccf26(f={closure_env#0} @ 0x000000016fdf9660) at autorelease.rs:30:1
    frame #6: 0x00000001003cd61c wgpu-test2`wgpu_hal::metal::device::_$LT$impl$u20$wgpu_hal..Device$LT$wgpu_hal..metal..Api$GT$$u20$for$u20$wgpu_hal..metal..Device$GT$::create_render_pipeline::h6fc1dc22f43e56d7(self=0x0000000103076250, desc=0x000000016fdfb3d8) at device.rs:807:9
    frame #7: 0x0000000100142a14 wgpu-test2`wgpu_core::device::Device$LT$A$GT$::create_render_pipeline::h56def6f46007c4fe(self=0x0000000103076200, self_id=Id<wgpu_core::device::Device<wgpu_hal::empty::Api>> @ 0x000000016fdfc190, adapter=0x0000000103055408, desc=0x000000016fdfd720, implicit_context=Option<wgpu_core::device::ImplicitPipelineContext> @ 0x000000016fdfcb08, hub=0x0000000103046810, token=0x000000016fdfc53f) at mod.rs:3030:22
    frame #8: 0x00000001001cb49c wgpu-test2`wgpu_core::device::_$LT$impl$u20$wgpu_core..hub..Global$LT$G$GT$$GT$::device_create_render_pipeline::hdec4b715a29111ff(self=0x0000000103046810, device_id=Id<wgpu_core::device::Device<wgpu_hal::empty::Api>> @ 0x000000016fdfd248, desc=0x000000016fdfd720, id_in=<unavailable>, implicit_pipeline_ids=Option<wgpu_core::device::ImplicitPipelineIds<wgpu_core::hub::IdentityManagerFactory>> @ 0x000000016fdfd258) at mod.rs:4938:34
    frame #9: 0x00000001002cf0e4 wgpu-test2`_$LT$wgpu..backend..direct..Context$u20$as$u20$wgpu..context..Context$GT$::device_create_render_pipeline::h2b743d44cc14811b(self=0x0000000103046810, device=0x000000016fdfdda0, device_data=0x000060000020d240, desc=0x000000016fdfe750) at direct.rs:1174:27
    frame #10: 0x00000001002dd4ec wgpu-test2`_$LT$T$u20$as$u20$wgpu..context..DynContext$GT$::device_create_render_pipeline::h10d77c249d5b5eba(self=0x0000000103046810, device=0x000000016fdfe348, device_data=&(dyn core::any::Any + core::marker::Send + core::marker::Sync) @ 0x000000016fdfddc0, desc=0x000000016fdfe750) at context.rs:2191:13
    frame #11: 0x00000001000c605c wgpu-test2`wgpu::Device::create_render_pipeline::hd25f1cfca56bd068(self=0x000000016fdfe328, desc=0x000000016fdfe750) at lib.rs:2055:26
    frame #12: 0x000000010000a8e0 wgpu-test2`wgpu_test2::main::h46081c84012a4b20 at main.rs:80:21
    frame #13: 0x00000001000042b8 wgpu-test2`core::ops::function::FnOnce::call_once::h6cfae6d08c229c4a((null)=(wgpu-test2`wgpu_test2::main::h46081c84012a4b20 at main.rs:8), (null)=<unavailable>) at function.rs:250:5
    frame #14: 0x0000000100007104 wgpu-test2`std::sys_common::backtrace::__rust_begin_short_backtrace::h6a73e894eb6c4a0d(f=(wgpu-test2`wgpu_test2::main::h46081c84012a4b20 at main.rs:8)) at backtrace.rs:121:18
    frame #15: 0x000000010000b5e4 wgpu-test2`std::rt::lang_start::_$u7b$$u7b$closure$u7d$$u7d$::h0d1793a52b968c38 at rt.rs:166:18
    frame #16: 0x00000001006eaf48 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] core::ops::function::impls::_$LT$impl$u20$core..ops..function..FnOnce$LT$A$GT$$u20$for$u20$$RF$F$GT$::call_once::h475731f7094d3540 at function.rs:287:13 [opt]
    frame #17: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] std::panicking::try::do_call::h12bf4403d16a6a4a at panicking.rs:487:40 [opt]
    frame #18: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] std::panicking::try::h18bf560b5f72e041 at panicking.rs:451:19 [opt]
    frame #19: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] std::panic::catch_unwind::hcbe48bb64ad0be62 at panic.rs:140:14 [opt]
    frame #20: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] std::rt::lang_start_internal::_$u7b$$u7b$closure$u7d$$u7d$::h8e727056af92dfee at rt.rs:148:48 [opt]
    frame #21: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] std::panicking::try::do_call::h79bb23a7a8fc1ffe at panicking.rs:487:40 [opt]
    frame #22: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] std::panicking::try::h6f847ef34bd6a546 at panicking.rs:451:19 [opt]
    frame #23: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 [inlined] std::panic::catch_unwind::h784da673948b3f7f at panic.rs:140:14 [opt]
    frame #24: 0x00000001006eaf40 wgpu-test2`std::rt::lang_start_internal::hed1c56e4b4db0361 at rt.rs:148:20 [opt]
    frame #25: 0x000000010000b5b0 wgpu-test2`std::rt::lang_start::h860dcbdb734f25e3(main=(wgpu-test2`wgpu_test2::main::h46081c84012a4b20 at main.rs:8), argc=1, argv=0x000000016fdfef80, sigpipe='\0') at rt.rs:165:17
    frame #26: 0x000000010000a998 wgpu-test2`main + 36
    frame #27: 0x000000018bc1fe50 dyld`start + 2544
(lldb) ^D

Platform
M1 Pro running macOS Ventura 13.2.1
cargo 1.69.0-nightly (9880b408a 2023-02-28)

[dependencies]
pollster = "0.3.0"
wgpu = "0.15.1"
winit = "0.28.1"

[teoxoy]

Thanks for the detailed report!

I see now that a wgsl vertex shader is required to return a position (https://www.w3.org/TR/WGSL/#function-restriction), however I still would've expected an error message instead of a fault.

It seems we are missing this validation from naga.