Sort out throwing errors from DOM bindings

[jdm]

There are lots of XXXs and commented out calls to js_GetErrorMessage in the generated code. We need to sort out what to do, with the end goal of throwing the right kind of error according the the relevant spec.

[jdm]

The easiest path forward for now is to add some limited wrappers in rust-mozjs that call JS_ReportError with well-defined sets of parameters, according to our needs.

[jdm]

@bfrohs This would be a really useful piece of work you could do. The generated bindings code is full of places where we just return 0 with a commented out call to JS_ReportError.

[0b10011]

Sounds good. After I get my two current PRs finished up, I'll look into it more. Thanks for the suggestion!

[jdm]

As of rust-lang/rust#2057 we can now write bindings for variadic functions! \o/

[brunoabinader]

I wonder if #1542 is a duplicate of this issue - DOMException skeleton is now available.

[jdm]

No, I'm pretty certain that DOMException interacts with error event handlers on the content side, whereas this issue revolves around fixing the places in generated code where we currently just return false without calling anything like JS_ReportError.

[Ms2ger]

There's still issues with DOMException too; we throw a plain Error right now (in throw_method_failed_with_details).

[Ms2ger]

Current status: we have throw_type_error working correctly; we just need someone to replace the XXXjdm comments in CodegenRust.py by throw_type_error calls (with strings from src/components/script/dom/bindings/codegen/Errors.msg).

[plaublin]

I am currently working on this problem.

[plaublin]

I was going to do a pull request but found out that the code changed a little bit since last month.
In my branch I call throw_type_error, but in the main branch there are some comments to ThrowErrorMessage (diff: https://github.com/schaars/servo/compare/dom_throw_error). So I was wondering if I should modify the calls to throw_type_error by calls to ThrowErrorMessage or not?

[Ms2ger]

No, those changes look good to me. (Please do rebase and squash your branch before creating the PR.)