[hal/dx12] Mesh Shaders

[SupaMaggie70Incorporated]

Connections
Addresses #7219, a sub-issue of #7197

Description
This adds a DX12 backend for mesh shaders

Current issues:

• Limits aren't calculated properly
• In the pipeline stream descriptor, we could figure out the maximum length and possibly avoid allocations and vec's if that's desirable

Testing
I have updated the mesh shader example to use DXILpassthrough to test this, and it works.

Squash or Rebase?
Squash

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

[SupaMaggie70Incorporated]

@cwfitzgerald Any chance a review for this could happen soon-ish? I'm waiting on it to continue working on both my PRs #8139 and #8206, since they will modify many of the same files.

[cwfitzgerald]

I should be able to re-review it today.

[SupaMaggie70Incorporated]

@cwfitzgerald Going to ping you again, not super urgent but it is something I'd like to get reviewed soon-ish.

[Copilot]

Pull Request Overview

This PR adds DirectX12 backend support for mesh shaders, expanding WGPU's mesh shader capabilities beyond Vulkan. The implementation includes direct draw commands, indirect draw variants, and proper pipeline state handling for both task and mesh shaders.

• Implements mesh shader pipeline creation using D3D12's pipeline stream API
• Adds mesh shader draw command implementations (direct and indirect variants)
• Updates examples and tests to support both Vulkan and DX12 backends

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
wgpu-hal/src/dx12/mod.rs	Adds mesh shader pipeline state stream structure and command signature support
wgpu-hal/src/dx12/device.rs	Implements mesh shader pipeline creation and command signature setup
wgpu-hal/src/dx12/command.rs	Implements mesh shader draw commands (direct and indirect variants)
wgpu-hal/src/dx12/adapter.rs	Adds mesh shader feature detection and limit configuration
tests/tests/wgpu-gpu/mesh_shader/mod.rs	Updates tests to support both Vulkan and DX12 backends with shader compilation
examples/features/src/mesh_shader/mod.rs	Updates example to support DX12 backend with HLSL shader compilation
naga/src/back/hlsl/mod.rs	Adds HLSL stage string mappings for task and mesh shaders

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[cwfitzgerald]

Got some nits, but we're good here once those are resolved.

[SupaMaggie70Incorporated]

@cwfitzgerald I've addressed all comments I think. Good to merge?

[cwfitzgerald]

CI mad

[SupaMaggie70Incorporated]

@cwfitzgerald Should be good now lmao