extensions/typescript-language-features/src/tsServer/bufferSyncSupport.ts/TabResourceTracker/has
class TabResourceTracker:	public has(resource: vscode.Uri): boolean {
		if (resource.scheme === vscodeNotebookCell) {
			const notebook = vscode.workspace.notebookDocuments.find(doc =>
				doc.getCells().some(cell => cell.document.uri.toString() === resource.toString()));

			return !!notebook && this.has(notebook.uri);
		}

		const entry = this._tabResources.get(resource);
		return !!entry && entry.tabs.size > 0;
	}