src/vs/workbench/contrib/notebook/common/notebookEditorInput.ts/NotebookEditorInput/_suggestName
class NotebookEditorInput:	private async _suggestName(provider: NotebookProviderInfo, suggestedFilename: string) {
		// guess file extensions
		const firstSelector = provider.selectors[0];
		let selectorStr = firstSelector && typeof firstSelector === 'string' ? firstSelector : undefined;
		if (!selectorStr && firstSelector) {
			const include = (firstSelector as { include?: string }).include;
			if (typeof include === 'string') {
				selectorStr = include;
			}
		}

		if (selectorStr) {
			const matches = /^\*\.([A-Za-z_-]*)$/.exec(selectorStr);
			if (matches && matches.length > 1) {
				const fileExt = matches[1];
				if (!suggestedFilename.endsWith(fileExt)) {
					return joinPath(await this._fileDialogService.defaultFilePath(), suggestedFilename + '.' + fileExt);
				}
			}
		}

		return joinPath(await this._fileDialogService.defaultFilePath(), suggestedFilename);
	}