Removes the nullable attribute from window.parent

[orta]

Re: microsoft/TypeScript#44684 (comment)

I read the spec, and it really didn't seem like null was possible - it is either the parent, or itself:

https://dev.w3.org/html5/spec-LC/browsers.html#dom-parent

The parent IDL attribute on the Window object of a Document in a browsing context b must return the WindowProxy object of the parent browsing context, if there is one (i.e. if b is a child browsing context), or the WindowProxy object of the browsing context b itself, otherwise (i.e. if it is a top-level browsing context or a detached nested browsing context).

Maybe this could be true in environments other than dom?

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged.

[saschanaz]

This is the latest spec: https://html.spec.whatwg.org/multipage/browsers.html#dom-parent

It has an example, which I modified to allow copy-pasting to console:

var element = document.createElement("iframe");
document.body.append(element);
var iframeWindow = element.contentWindow;
element.remove();

console.log(iframeWindow.top === null);
console.log(iframeWindow.parent === null);
console.log(iframeWindow.frameElement === null);

All returns true. But admittedly a rare situation, so your call. I guess at least it should be in the comment that it can be null?

[orta]

Yeah, thanks for digging!

I'll add a comment saying it's possibly null - I think this is probably worth the ergonomics change

[saschanaz]

Should it say why it's not nullable in the lib file?

[saschanaz]

How about:

Refers to either the parent WindowProxy, or itself.

It can rarely be null e.g. for contentWindow of an iframe that is already removed from the parent.

[orta]

Having it multiline doesn't really work because it's in two places with different indentations, so I made this a single line

[saschanaz]

I think \n automatically does the indentation.

[saschanaz]

e.g. postMessage

[saschanaz]

LGTM

[github-actions]

Merging because @saschanaz is a code-owner of all the changes - thanks!