wgpu-core Result values are quite large

[jimblandy]

As reported by newer versions of Clippy via the result_large_err lint, several of the error types returned in wgpu-core are quite large. For example:

error: the `Err`-variant returned from this function is very large
    --> wgpu-core/src/command/render.rs:1023:10
     |
1023 |     ) -> Result<(UsageScope<A>, SurfacesInDiscardState), RenderPassErrorInner> {
     |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the `Err`-variant is at least 208 bytes
     |
     = help: try reducing the size of `command::render::RenderPassErrorInner`, for example by boxing large elements or replacing it with `Box<command::render::RenderPassErrorInner>`
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#result_large_err

As the Clippy help explains:

A Result is at least as large as the Err-variant. While we expect that variant to be seldomly used, the compiler needs to reserve and move that much memory every single time.

[cwfitzgerald]

Did this get fixed by a recent PR from you?

[ErichDonGubler]

@cwfitzgerald: AIUI, #3226 (which I presume you're referring to) was intended to stave off the immediate CI blocker that this lint would introduce from MSRV 1.65 onwards. I don't think any work has been done to actually establish that lint itself or its default size threshold is desirable for this project specifically, though.

I think it would be interesting to validate whether or not the workaround that #3226 intends is actually a good long-term solution. Perhaps we can change the scope of this issue to handle that instead?