Previews, as seen when this build job started (d26e47c):
WebGPU _{webgpu.idl | Explainer | Correspondence Reference}
WGSL _{grammar.js | wgsl.lalr.txt}

cc @toji @litherum

I started updating this to have an exception object that we could extend in the future to provide structured error data if we want to. However, I ended up realizing there are guidelines that prevent us from doing so.

WebIDL doesn't allow defining custom exception types:

An exception is a type of object that represents an error and which can be thrown or treated as a first class value by implementations. Web IDL does not allow exceptions to be defined, but instead has a number of pre-defined exceptions that specifications can reference and throw in their definition of operations, attributes, and so on. Exceptions have an error name, a DOMString, which is the type of error the exception represents, and a message, which is an optional, user agent-defined value that provides human readable details of the error.
https://webidl.spec.whatwg.org/#idl-exceptions

Meanwhile the Promises guide says:

Rejection reasons must be Error instances
Promise rejection reasons should always be instances of the JavaScript Error type, just like synchronously-thrown exceptions should always be instances of Error. This generally means using either one of the built-in JavaScript error types, or using DOMException.
https://www.w3.org/2001/tag/doc/promises-guide#reasons-should-be-errors

I believe this doc is more-or-less authoritative. Unfortunately, the somewhat more maintained Design Principles don't say much:
https://w3ctag.github.io/design-principles/#error-types

Technically, I'm sure it's possible to create a plain Error object, hang properties off of it, and return it, but that's a workaround. The Promises guide is a pretty good indicator we're not expected to go in this direction.

I haven't thought of any good alternatives yet.