Description

wgpu 30.0.0's BrowserWebGpu error decoder handles GPUValidationError and GPUOutOfMemoryError, but not the WebGPU-specified GPUInternalError. If GPUDevice.popErrorScope() resolves with that third error subclass, wgpu::Error::from_js reaches panic!("Unexpected error") even though wgpu already exposes Error::Internal.

The vendored webgpu_sys subset also omits the generated GpuInternalError binding, so the decoder cannot add the corresponding typed branch without first vendoring/exporting it.

This is separate from the nullable clean-scope binding regression reported at wasm-bindgen/wasm-bindgen#5234.

Repro steps

The fixture is self-contained and MIT-licensed. No product code or other private code is required; the surrounding project repository is private, so the exact method and results are included here.

The deterministic BrowserWebGpu integration test:

1. requests a real adapter/device and enters the production wgpu bootstrap/error-scope path;
2. saves and wraps the real GPUDevice.prototype.popErrorScope;
3. awaits the original browser promise;
4. substitutes new GPUInternalError("alpine synthetic internal error") for the internal-scope result; and
5. verifies that the patched Rust decoder produces wgpu::Error::Internal, preserves the message, and does not contain Unexpected error or unreachable.

This synthetic substitution exercises the real browser-native error class, real Promise boundary, and production Rust decoder. It intentionally proves only the returned-value type/mapping boundary; it does not claim to induce or reproduce an organic browser/driver internal fault.

The stock v30.0.0 source has no GpuInternalError branch and therefore deterministically falls through to the panic. The synthetic browser assertion was run against the patched build; the current stock build also encounters the independent clean-null regression before this injected internal result.

The standalone fixture's exact three-row clean-scope control matrix is:

The matrix is included to establish the exact runtime and explain why the patched-current row is used to reach the separate synthetic internal-error decoder test. It is not evidence that a browser organically produced GPUInternalError.

Expected vs observed behavior

Expected: a GPUInternalError result is returned as wgpu::Error::Internal and its browser message is preserved.

Observed in stock v30 decoding: the object matches neither of the two handled subclasses and reaches panic!("Unexpected error"). With the local three-part patch, the synthetic result maps to an internal GPU error containing the exact synthetic message and produces no panic, unreachable trap, or unhandled rejection.

Relevant source/spec locations:

• WebGPU GPUInternalError: https://www.w3.org/TR/webgpu/#gpuinternalerror
• wgpu v30 decoder (validation, OOM, then panic): https://github.com/gfx-rs/wgpu/blob/v30.0.0/wgpu/src/backend/webgpu.rs#L74-L87
• existing wgpu::Error::Internal: https://github.com/gfx-rs/wgpu/blob/v30.0.0/wgpu/src/api/device.rs#L896-L924
• current generated web-sys GpuInternalError binding: https://github.com/wasm-bindgen/wasm-bindgen/blob/0.2.126/crates/web-sys/src/features/gen_GpuInternalError.rs#L5-L34
• wgpu's vendored web-sys feature list, which omits it: https://github.com/gfx-rs/wgpu/blob/v30.0.0/xtask/src/vendor_web_sys.rs
• the adjacent clean-scope conversion site: https://github.com/gfx-rs/wgpu/blob/v30.0.0/wgpu/src/backend/webgpu.rs#L1064-L1068

Suggested fix:

1. vendor and export gen_GpuInternalError.rs in the pinned BrowserWebGpu binding subset;
2. add a dyn_ref::<GpuInternalError>() branch mapping its message to Error::Internal; and
3. add a browser regression test covering all three WebGPU error subclasses.

Related but not duplicate: #2170 tracks broad historical spec compliance; #4866/#5160 add the input ErrorFilter::Internal; #2299 introduced error scopes; #9090 refreshed the vendored binding subset without this class; and #9683 is an organic producer-side MSL error rather than a Rust returned-value decoder bug.

Temporary workaround: pinning wasm-bindgen/CLI 0.2.122, wasm-bindgen-futures 0.4.72, and js-sys/web-sys 0.3.99 avoids the sibling clean-null regression, but it does not add GPUInternalError mapping. The internal-error path still needs a local wgpu patch or upstream fix.

Extra materials

No screenshots, validation logs, GPU captures, or product assets are required. The failure is at the JavaScript-class/Rust-decoder boundary.

Platform

• Rust 1.96.0, target wasm32-unknown-unknown
• wgpu 30.0.0, BrowserWebGpu backend
• wasm-bindgen 0.2.126
• wasm-bindgen-futures 0.4.76
• js-sys/web-sys 0.3.103
• wasm-bindgen CLI 0.2.126
• Node 24.18.0
• Playwright 1.58.2
• Chromium 145.0.7632.6, Playwright browser revision 1208