src/vs/editor/contrib/snippet/snippetSession.ts/OneSnippet/_hasPlaceholderBeenCollapsed
class OneSnippet:	private _hasPlaceholderBeenCollapsed(placeholder: Placeholder): boolean {
		// A placeholder is empty when it wasn't empty when authored but
		// when its tracking decoration is empty. This also applies to all
		// potential parent placeholders
		let marker: Marker | undefined = placeholder;
		while (marker) {
			if (marker instanceof Placeholder) {
				const id = this._placeholderDecorations!.get(marker)!;
				const range = this._editor.getModel().getDecorationRange(id)!;
				if (range.isEmpty() && marker.toString().length > 0) {
					return true;
				}
			}
			marker = marker.parent;
		}
		return false;
	}