Add webidl2js‑globals.js to automate install of [Exposed] globals

[ExE-Boss]

TODO:

• Fix the interface order determination algorithm so that Element goes after Node and EventTarget, but before HTMLElement.
• Improve the efficiency of the interface order determination algorithm.

Depends on:

• Implement support for [LegacyWindowAlias] and [NoInterfaceObject] #191 (merged)
• Implement support for the [Exposed] extended attribute #192 (merged)

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Supersedes and closes #101.

review?(@TimothyGu)

[TimothyGu]

Perhaps we can be a bit less ambitious, and separate out the parts that add [Exposed] support to install() (which I mentioned in #191) from the parts that aggregates globals into the same file? This way we could immediately start using it in jsdom.

WRT an algorithm to figure out the require order, if the dependency graph turns out to be acyclic then topological sorting should work. If it is cyclic then… we’d have to look into other things.

[ExE-Boss]

The dependency order is already enforced to be acyclic in:

webidl2js/lib/constructs/interface.js

Lines 468 to 478 in 5af205c

	// All interfaces an object of this interface implements.
	* allInterfaces(seen = new Set([this.name]), root = this.name) {
	yield this.name;
	if (this.idl.inheritance && this.ctx.interfaces.has(this.idl.inheritance)) {
	if (seen.has(this.idl.inheritance)) {
	throw new Error(`${root} has an inheritance cycle`);
	}
	seen.add(this.idl.inheritance);
	yield* this.ctx.interfaces.get(this.idl.inheritance).allInterfaces(seen, root);
	}
	}

[TimothyGu]

I've rebased this, but it doesn't look like it's ready for review yet? Interface files call webidl2jsGlobal.setupGlobal but it's not defined.

[ExE-Boss]

@TimothyGu That’s a leftover from before I renamed it to just installInterfaces, which is more descriptive of what it does.