Question about WGPUBindGroupLayoutEntry struct mismatch with webgpu.h from Google Dawn

[DomagojKudek]

When trying to build a Dawn web-gpu-based project with Emscripten targeting a wasm build and using dear ImGui, the built app complains about the "assert(entryPtr);" line on one of ImGuis WGPUBindGroupLayoutEntries.

App.js :

function makeEntry(entryPtr) {
       assert(entryPtr);
       // bindingArraySize is not specced and thus not implemented yet. We don't pass it through
       // because if we did, then existing apps using this version of the bindings could break when
       // browsers start accepting bindingArraySize.
       var bindingArraySize = HEAPU32[(((entryPtr)+(16))>>2)];
       assert(bindingArraySize == 0 || bindingArraySize == 1);
 
       return {
         "binding":
           HEAPU32[(((entryPtr)+(4))>>2)],
         "visibility":
           HEAPU32[(((entryPtr)+(8))>>2)],
         "buffer": makeBufferEntry(entryPtr + 24),
         "sampler": makeSamplerEntry(entryPtr + 48),
         "texture": makeTextureEntry(entryPtr + 56),
         "storageTexture": makeStorageTextureEntry(entryPtr + 72),
       };
     }

When looking at the included emscripten webgpu header file:

emscripten/system/include/webgpu/webgpu.h

Line 1204 in eda083a

typedef struct WGPUBindGroupLayoutEntry {

It seems that it's missing the bindingArraySize in the WGPUBindGroupLayoutEntry struct compared to Dawn's webgpu.h file.

Is that the issue for my problem, or is something else at play that's not related to Emscripten itself?

[kainino0x]

If you are using --use-port to link Emdawnwebgpu, then you're not using Emscripten's copy of webgpu.h (which is old), but Emdawnwebgpu's copy. The include order should prevent mixing the old webgpu.h with the new implementation.
(see #24265)

There isn't a super convenient link to look at the latest version of that (yet) but you can find it in the download:
https://github.com/google/dawn/releases
and I have a snapshot here:
https://github.com/kainino0x/webgpu-cross-platform-demo/blob/main/emdawnwebgpu_pkg/webgpu/include/webgpu/webgpu.h

If the header and implementation are not out of sync, then I guess there is some issue with Dear ImGui? I think it would mean WGPUBindGroupDescriptor.entries is nullptr which is weird.

[sbc100]

Is it time to rip out the old webgpu stuff from emscripten maybe?

[kainino0x]

Very soon. I have a list of known bugs I'd like to fix so we don't foist a known-buggy implementation on people.
I thought I would get them done this week but forgot I would be on-call and unfortunately I don't think I can finish them for another few weeks.