const result = ts.transform(ts.createSourceFile("file.ts", `let content!: string;`, ts.ScriptTarget.ES2016), [() => f => f]);
    const printer = ts.createPrinter({}, {
        onEmitNode: result.emitNodeWithNotification,
        substituteNode: result.substituteNode
    });
    const txt = printer.printFile(result.transformed[0]);