useDefineForClassFields: false can set members in wrong constructor

[kryops]

Describe the bug

Hi there,

we noticed a transpilation error when executing our code via swc-node.

We have a class that returns a different class in one of its methods. The issue we noticed was that some class members were missing at runtime. After some debugging, we noticed that the property assignment is placed inside the wrong constructor (i.e. the one from the other class that is returned in a method). It looks like the properties are always put into the first constructor inside the class declaration - it works correctly if I place the class' own constructor above the method.

The issue only seems to occur when using "useDefineForClassFields": false, which is the default setting in swc-node.

Thanks for looking into it!

Input code

class MyClass {
 // also same behavior for static methods
 methodReturningClass() {
    return class SomeOtherClass {
      constructor() {
        // Assignment to foo goes here
      }
    };
  }
  
  constructor(args) {
    // Assignment to foo should go here
  }

  foo = 'bar'
}

Config

{
  "jsc": {
    "target": "es2018",
    "externalHelpers": false,
    "parser": {
      "syntax": "ecmascript",
      "jsx": true
    },
    "transform": {
      "legacyDecorator": true,
      "decoratorMetadata": false,
      "useDefineForClassFields": false,
      "react": {
        "runtime": "classic"
      }
    },
    "keepClassNames": true,
    "paths": {},
    "loose": false,
    "minify": {
      "compress": false
    }
  },
  "minify": false,
  "isModule": true,
  "module": {
    "type": "commonjs",
    "noInterop": false
  }
}

Playground link (or link to the minimal reproduction)

https://play.swc.rs/?version=1.4.12&code=H4sIAAAAAAAAA22OzQrCMAzH732K3KanPYB4EM8i6BN0XWwLWwNJJoj03e3qNhD8Qz7Ixy9xgxWBy%2Btc49tA24IdhEDsiNBhsM9IDI9iolajgxE1UC9mSW6oE6eYfCXs9jOjiGsZXMXeacSrBuTtSpWjJMqTU%2BJtb1Z54SQSfRoxKSiV6wSeUKAgcBnLNeaD%2BabmF2fZy4r8i5NA09AX6srMpri5c4Sms9yY%2FAE1Rc7IGwEAAA%3D%3D&config=H4sIAAAAAAAAA2WRy07DQAxF9%2F2KaNYsgBViS1XBovyDNbkpU%2BYl25EaRfl3JmkSEtjNXNvn%2BtEfqspcxZrXqi%2FP8lHiC7T8DeT58enFPNx13BQcyb%2FDZ7CUhIa8YI5mYgGvlKJIF5VuE8cGEssu68yaLMeQcotJGWaMMkVpEoctyeNCtjvCJiZNPNetqHoJnKFUk9K%2BtZLRCo5oXMQp8ZsnkZODr%2BVfHoOsbpxHqY3qAsYx7FjprJmDw67xbyBP6E8KkF2LZTf6NUr9kuxTEvxZYHDRNd12bJtCZsja5mFxnTC%2FBSvFODmnuvXY2JuwKMt5u3yfJoWQ4lWW88b0EcuBU97YDYfhB0yjMHcgAgAA

SWC Info output

No response

Expected behavior

"use strict";
let MyClass = class MyClass {
    methodReturningClass() {
        return class SomeOtherClass {
            constructor(){}
        };
    }
    constructor(args){
         this.foo = 'bar';
    }
};

Actual behavior

"use strict";
let MyClass = class MyClass {
    methodReturningClass() {
        return class SomeOtherClass {
            constructor(){
                this.foo = 'bar';
            }
        };
    }
    constructor(args){}
};

Version

1.4.12

Additional context

No response

[kryops]

Update: The issue also seems to occur when setting "loose": true instead of "useDefineForClassFields": false

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.