Option to preserve original decorators (no transpiling)

[nashwaan]

TypeScript Version: 2.6.2

Code

I like Typescript for all its advertised advantages and specially, it is a superset for ESNext javascript.

But I am facing one issue in the transpiled code.
I would like you to add an option to preserve original decorators in the emitted code.

Say I have the following class Greeter in greeter.ts:

function clsDecorator(constructor: Function) {
  Object.seal(constructor);
}

function funDecorator(value: boolean) {
  return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
      descriptor.enumerable = value;
  };
}

@clsDecorator
class Greeter {
  greeting: string;
  constructor(message: string) {
    this.greeting = message;
  }
  @funDecorator(false)
  greet() {
    return 'Hello, ' + this.greeting;
  }
}

But how to keep class and function decorators in the output and not introduce __decorate code?

Expected behavior:

I want to get this greeter.js output (which is correct ESNext syntax when experimental decorator is enabled, and it can be consumed by babel):

function clsDecorator(constructor) {
  Object.seal(constructor);
}

function funDecorator(value) {
  return function(targe, propertyKey, descriptor) {
    descriptor.enumerable = value;
  };
}

@clsDecorator
class Greeter {
  greeting;
  constructor(message) {
    this.greeting = message;
  }
  @funDecorator(false)
  greet() {
    return 'Hello, ' + this.greeting;
  }
}

Actual behavior:

But currently I get this output using tsc greeter.ts --target ESNext (which is good for the general case):

var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
    return c > 3 && r && Object.defineProperty(target, key, r), r;
};
function clsDecorator(constructor) {
  Object.seal(constructor);
}
function funDecorator(value) {
  return function (target, propertyKey, descriptor) {
    descriptor.enumerable = value;
  };
}
let Greeter = class Greeter {
  constructor(message) {
    this.greeting = message;
  }
  greet() {
    return 'Hello, ' + this.greeting;
  }
};
__decorate([
  funDecorator(false)
], Greeter.prototype, "greet", null);
Greeter = __decorate([
  clsDecorator
], Greeter);

[j-oliveras]

Duplicate of #16882 and #18713.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.