WGSL: Support the pointer_composite_access language extension

[rcoreilly]

Description

The WGSL spec has a requires directive to request language extensions, such as pointer_composite_access https://www.w3.org/TR/WGSL/#language-extensions-sec

When I put that at the top of my .wgsl shader, it barfs:

[wgpu] [Error] Device::create_shader_module error: 
Shader 'squares' parsing error: expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file, found 'requires'
  ┌─ wgsl:2:1
  │
2 │ requires pointer_composite_access;
  │ ^^^^^^^^ expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file

I would particularly be interested in when that specific language extension pointer_composite_access will be included as well -- huge improvement in usability. Also unrestricted_pointer_parameters seems rather important if I understand it properly, which I'm not sure I do..

Repro steps
add that line to the top of any .wgsl code.

Expected vs observed behavior

didn't work.

Platform

Mac OS, latest trunk HEAD 26398ea using naga cli, and v0.19.4.1 of wgpu-native.

[ErichDonGubler]

@rcoreilly: Basic support for parsing requires is now posted in #6437. As the scope of parsing is in #6350, I'll narrow the scope of this issue (and edit the OP) to just the pointer_composite_access extension.

[sagudev]

I am working on this.

[ErichDonGubler]

@sagudev: Sweet! I'll plan on reviewing your PRs. It might be next year when I have bandwidth to do so, but I think it's the same for all the Firefox WebGPU/Naga team. 😅

[sagudev]

It would be nice to get #6814 landed before (holidays).

[sagudev]

I think we need to remove all usages of Error::Pointer, ex:

wgpu/naga/src/front/wgsl/lower/mod.rs

Line 1981 in ee3ae0e

return Err(Error::Pointer(

Also I think some types of expressions are already supported, so It would be really interesting to see CTS results with pointer_composite_access reported as supported but otherwise unimpl.