Linkify "present" for dictionaries

[domenic]

Today I helped some people figure out a Chrome bug that was a result of not correctly using the C++ equivalent of "present" for dictionaries in our implementation of https://fetch.spec.whatwg.org/#dom-request . They weren't sure whether given { referrer: undefined }, if referrer was "present" or not. People didn't know that Web IDL was the place to look for what this means.

I think we should encourage more specs to link to https://heycam.github.io/webidl/#dfn-present as a way of helping with this. (Maybe via a public-script-coord announcement?) But to start Fetch could set an example.

[annevk]

I've been bitten a couple times by IDL refactoring removing things. How stable is this?

(Last time was that we added mapping for record and then we got rid of it in favor of Infra. Makes sense of course, but only found out about it due breakage.)

[domenic]

It should be quite stable. It's used all over the place, just without links to it.

[annevk]

I mean, I could imagine dictionaries becoming maps or using the "exists" language. But okay.

[domenic]

Oh, fair point. After thinking about that for a bit, I think we'll be safe, since the idea of "present" is a bit more complicated. Even if it is specifically defined to mean "when the underlying map entry exists", I think we'll still want to keep a specialized term for dictionaries since we want to talk about the interaction with undefined and default values and such. E.g. when people click on the "present" link it should go to something in Web IDL that talks about all those considerations, instead of going to somewhere in Infra that is much more abstract.

[annevk]

Turns out that within a year we flipped on this a bit and exists is now the way to go: whatwg/webidl#524.