Editorial: combine safety check steps into new section

[marcoscaceres]

Closes #237

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[annevk]

You should make these throw an exception. Web IDL will do the conversion from a thrown exception to a rejected promise. Returning an exception is very weird.

Alternatively you could return a(n) (string) enum and branch on that.

[marcoscaceres]

Ok, yeah, good point... will make them throw directly.

[marcoscaceres]

Ok, sooooo... these all throw now. And yes, the IDL layer would automatically wrap the exceptions.

However, just from the sake of clarity and consistency, I'd still like to use "Return a promise rejected with X" for .lock(). I've had instances in the past of reviewers getting confused about methods throwing even though they always return a promise.

Similarly, for .unlock(), just for clarity, I have it re-throw and abort the steps.

[annevk]

I guess that's okay, but I'd rather we explain the mechanism in a note so implementations with correct binding layers don't do this redundantly as well.

[marcoscaceres]

Yeah, it would be way cleaner. I'd also rather just be writing:

• If X throw {{WhateverError}}.
• If Y throw {{OtherError}}.

And so on... It feels like WebIDL's [=exception/throw=] should include such a note. Currently, it's not super clear what should happen and every example in WebIDL is using [=return a promise rejected with=].

I'll raise an issue on WebIDL.

[marcoscaceres]

Anyone interested whatwg/webidl#1301

[annevk]

It strikes me that if you adopt whatwg/html@2db564c here (and I think you should in a follow-up) you won't get to distinguish exceptions, but that's probably okay.

[marcoscaceres]

Yeah, that's ok. And yeah, will do that as a followup.

[annevk]

I guess that's okay, but I'd rather we explain the mechanism in a note so implementations with correct binding layers don't do this redundantly as well.