Fixed refs to decorated class from itself methods (legacy decorators)

[Amareis]

Q	A
Fixed Issues?	Fixes #11131
Patch: Bug Fix?	Yes
Major: Breaking Change?	No
Minor: New Feature?	No
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	No
License	MIT

Problem described in #11131
Solved by inserting in all methods (including static, #private ones and constructor) let ClassName = _someGeneratedVariable, where _someGeneratedVariable hold "final" class, after all decorators applied.

References in class properties still isn't supported.

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[JLHwung]

Can you add test cases on property? i.e.

@dec
@dec2
class Parent {
  property = Parent,
}

What will p.property be? Same for private properties.

[Amareis]

Solved by inserting in all methods (including static, #private ones and constructor) let ClassName = _someGeneratedVariable, where _someGeneratedVariable hold "final" class, after all decorators applied.
References in class properties still isn't supported.

Property isn't working currently (will hold undecorated class). For full solution we should replace all class references in read positions of class body to outer reference, but I ain't good enough at babel for such tricks.

[SuperOleg39]

Hi! Catch issue with property yesterday, similar to @JLHwung case, but with static property)

example source:

function dec(cls) {
  return cls
}

@dec
class Decorated {
  static property = Decorated
}

and output:

"use strict";

var _class, _class2, _temp;

function dec(cls) {
  return cls;
}

let Decorated = dec(_class = (_temp = _class2 = class Decorated {}, _class2.property = Decorated, _temp)) || _class;

This code produce runtime error ReferenceError: Cannot access 'Decorated' before initialization

[SuperOleg39]

@Amareis about class properties, fix references require changes in @babel/plugin-proposal-class-properties plugin?

[Amareis]

@Amareis about class properties, fix references require changes in @babel/plugin-proposal-class-properties plugin?

Don't think so. If we get full solution with replacing of original class reference in class body, this will be working without any additional efforts.

[xaviergonz]

@nicolo-ribaudo what's missing so this PR gets merged? just curious

[zachdaniel]

Would love to see this merged :)

[maccman]

Let's get this merged

[nicolo-ribaudo]

I was going to rebase and finish this, but I'm not sure that we should do it.

While I agree that the proposed behavior makes sense, the current behavior makes sense too:

// input.js
@dec class A { method() { A } }

// current.js
let A = dec(class A { method() { A } });

// proposed.js
let A = dec(class { method() { A } });

However, there is a big reason to keep the current behavior: changing it is not clearly a bugfix, and the code written in the past ~6 years relying on the current behavior risks to stop working.

I strongly encourage you to migrate to the current stage 3 version of the decorators proposal (https://github.com/tc39/proposal-decorators/), passing version: "2021-12" instead of version: "legacy" (or legacy: true) to the decorators plugin (https://babeljs.io/docs/en/babel-plugin-proposal-decorators#version).

[xaviergonz]

I'd say one good reason could be to be able to use babel to transpile typescript without a compatibility issue since this plugin is often used to do so. If the old behavior wants to be kept (understandable), then at least it could be offered as a "legacy-ts" mode or similar. Using the new stage 3 proposal would not fix the typescript compatibility issue.

[nicolo-ribaudo]

TypeScript plans to support standard decorators in the next version: microsoft/TypeScript#49074