Pin web-sys to 0.3.67 since we are using unstable APIs

[hecrj]

Connections

• Breaking changes in web-sys patch version 0.3.68 rustwasm/wasm-bindgen#3834

Description
wgpu relies on unstable APIs of the web-sys crate and the latest 0.3.68 version breaks types related to WebGPU.

Since semantic versioning isn't enforced for unstable APIs in web-sys, we should rely instead on a specific crate version to avoid broken builds in the future.

Testing
N/A

Checklist

• Run cargo fmt.
• Run cargo clippy. If applicable, add:
  • --target wasm32-unknown-unknown
  • --target wasm32-unknown-emscripten
• Run cargo xtask test to run tests.
• Add change to CHANGELOG.md. See simple instructions inside file.

[kpreid]

= version requirements are fragile. This will irreparably break builds for any dependent who has another dependency requiring a newer version of web_sys, and isn't even using the unstable apis part of wgpu (which could be webgl backend only, or even a non-web build that happens to also have an unused web_sys dep somewhere else).

This would be worthwhile if wgpu always used web_sys_unstable_apis, but it doesn't.

[hecrj]

It certainly will break builds for some users, but they will break upfront.

The current approach allows for Wasm builds to break after the fact, in code that has already been released.

In fact, 0.19 is actually broken right now.

[kpreid]

This imposes a very large cost on all users of only stable features ("don't upgrade your other dependencies") in order to benefit users of unstable features.

[kpreid]

Hmm, would it be possible to have two web-sys dependencies declared, one pinned and one not, and the pinned one only enabled when webgpu is enabled? If Cargo accepts that, it would handle both cases well.

[ErichDonGubler]

This doesn't solve the immediate problem, but: We currently plan on upgrading web-sys to address (see #5148, #5188). Notice that I was the one who filed rustwasm/wasm-bindgen#3816.

[nical]

It would be good to have a comment here explaining why we are pinning to a specific version.

[hecrj]

Hmm, would it be possible to have two web-sys dependencies declared, one pinned and one not, and the pinned one only enabled when webgpu is enabled? If Cargo accepts that, it would handle both cases well.

It may be possible with a bit of conditional compilation. I'll look into it.