fix(core): validate sample_count is 1 in Queue::write_texture

[ErichDonGubler]

This is a missing piece of the "validating texture buffer copy" routine, which is currently not outlined in the same way as the WebGPU spec.

It's almost certainly better to refactor writeTexture and other copy commands so that we can capture the routine and properly share it between different standard operations. This commit leaves this as future work, only fixing the missing validation in writeTexture.

Connections

• This was detected by runs of Firefox against the webgpu:api,validation,image_copy,buffer_texture_copies:sample_count:* CTS test.

Squash or Rebase?

Squash.

Checklist

• If this contains user-facing changes, add a CHANGELOG.md entry.

[ErichDonGubler]

A Rust MRE, if anyone is interested:

//! A Rust-y version of
//! [`webgpu:api,validation,queue,writeTexture:sample_count:*`](https://github.com/gpuweb/cts/blob/26530c7da1c48ea5d0bf4c5da83b15b996eb522f/src/webgpu/api/validation/queue/writeTexture.spec.ts#L60-L85).

use pollster::FutureExt as _;

fn main() {
    env_logger::init();

    let instance = wgpu::Instance::new(&wgpu::InstanceDescriptor::from_env_or_default());
    let adapter = instance
        .request_adapter(&Default::default())
        .block_on()
        .unwrap();
    let (device, queue) = adapter
        .request_device(&Default::default())
        .block_on()
        .unwrap();

    for sample_count in [1, 4] {
        let texture = device.create_texture(&wgpu::TextureDescriptor {
            label: None,
            size: wgpu::Extent3d {
                width: 16,
                height: 16,
                depth_or_array_layers: 1,
            },
            mip_level_count: 1,
            sample_count,
            dimension: wgpu::TextureDimension::D2,
            format: wgpu::TextureFormat::Bgra8Unorm,
            usage: wgpu::TextureUsages::COPY_DST | wgpu::TextureUsages::RENDER_ATTACHMENT,
            view_formats: &[],
        });

        let data = [0u8; 16];
        let size = wgpu::Extent3d {
            width: 1,
            height: 1,
            depth_or_array_layers: 1,
        };

        let is_valid = sample_count == 1;

        device.push_error_scope(wgpu::ErrorFilter::Validation);

        queue.write_texture(
            wgpu::TexelCopyTextureInfoBase {
                texture: &texture,
                mip_level: 0,
                origin: Default::default(),
                aspect: Default::default(),
            },
            &data,
            Default::default(),
            size,
        );

        match (is_valid, device.pop_error_scope().block_on()) {
            (true, None) | (false, Some(..)) => (),
            (expected_valid, err_opt) => panic!(
                concat!(
                    "expected valid = {} for `sample_count` = {}, ",
                    "but error scope yielded {:?}"
                ),
                expected_valid, sample_count, err_opt
            ),
        }
    }
}

[cwfitzgerald]

Couldyoumaybeaddthatasavalidationtestmaybe?

[andyleiserson]

This fix is also included in #7948.

[ErichDonGubler]

@cwfitzgerald:

Couldyoumaybeaddthatasavalidationtestmaybe?

Does…the relevant CTS test being added to CI not count? 🤔