Consider having Document extending Graph

[donmccurdy]

Currently the Document holds a reference to a Graph, from the property-graph package:

glTF-Transform/packages/core/src/document.ts

Lines 76 to 94 in a7c1dec

	private _graph: Graph<Property> = new Graph<Property>();
	private _root: Root = new Root(this._graph);
	private _logger: ILogger = Logger.DEFAULT_INSTANCE;
	/**
	* Enables lookup of a Document from its Graph. For internal use, only.
	* @internal
	* @experimental
	*/
	private static _GRAPH_DOCUMENTS = new WeakMap<Graph<Property>, Document>();
	/**
	* Returns the Document associated with a given Graph, if any.
	* @hidden
	* @experimental
	*/
	public static fromGraph(graph: Graph<Property>): Document | null {
	return Document._GRAPH_DOCUMENTS.get(graph) || null;
	}

To keep function parameter simple though, we sometimes need to look up a Document from an arbitrary Property...

glTF-Transform/packages/functions/src/list-texture-channels.ts

Lines 44 to 45 in a7c1dec

	export function getTextureChannelMask(texture: Texture): number {
	const document = Document.fromGraph(texture.getGraph())!;

... which works fine in general, but with Node.js continuing to delay the ecosystem from adopting ESM, it can be a source of hard-to-debug failures from dual package hazard. At some point I will need to drop CommonJS support entirely, but ...

It might be a nice simplification to merge the Document and Graph concepts by having Document extend Graph<Property>. Then there's one fewer concepts to think about, and one source of mystery bug in Node.js could go away. I think if I could do that and remove all use of instanceof, dual package hazard might not break end-user applications at all. May require a major release.