src/vs/workbench/services/userData/common/fileUserDataProvider.ts/FileUserDataProvider/open
class FileUserDataProvider:	open(resource: URI, opts: FileOpenOptions): Promise<number> {
		if (hasOpenReadWriteCloseCapability(this.fileSystemProvider)) {
			return this.fileSystemProvider.open(this.toFileSystemResource(resource), opts);
		}
		throw new Error('not supported');
	}