keepClassNames break class decorators

[falkenhawk]

Describe the bug

Hi, thanks for this great library and providing continuous support for it.
I have experienced an issue which I have been debugging for days.

jsc.keepClassNames breaks references, when class is decorated.

For example, creating new instance of a class, calling static method, uses the non-decorated class instead of the decorated one.

Here I try to provide the most concise and minimal reproduction I was able to come up with.

Input code

function CommonProp() {
  return <T extends { new (...args: any[]): {}; }>(Base: T) => {
    return class extends Base {
      public prop = 100;
    };
  };
}

@CommonProp()
class ClassX {
  public static checkX() {
    console.log(String(ClassX));
    console.log(new ClassX());
    // @ts-ignore
    console.log('class prop:', new ClassX().prop);
  }
}

ClassX.checkX();

Config

{
  "jsc": {
    "parser": {
      "syntax": "typescript",
      "decorators": true
    },
    "target": "es2020",
    "keepClassNames": true
  }
}

Playground link

https://play.swc.rs/?version=1.3.19&code=H4sIAAAAAAAAA2WPwWrDMBBE7wb%2Fw9wiQaukV7sJofmBQnMIlB5UVXFNnZWRZNpi9O%2BNurEJ5LILmtmnmeNAJraOsHOnk6Nn73ohMZYF4G0cPOFxD%2FsTLX0EjCD7DaGU0r4JFTT9vr7JCmOqkTbiSQdbYS%2Bx3jBhZphOhzBjsm8yAP3w3rUG%2FflnrPGwWtWspP%2BdZyqLstheBywLJu7yPDDrwglRx%2FMyn9Z8HaYqgHEUXGdV5xrxEn1LjeBjKetbR67Jspj15RLbGO7bhpy3tycLTpRrVIs7XBNUfmRMurRhSU0p6z%2Fl5TWZhwEAAA%3D%3D&config=H4sIAAAAAAAAAzXKOwqAMBAFwLu82kIs09p7hyU%2BxG%2FC7gqG4N3Vwm6KqVgsIlRkUaN%2BsnK4XAjwkmlR5%2BxoMDImFU9qCK4n7wYuOtHfSOvarn3TSuZ%2BE7NBdv7xfgBpgK6LZAAAAA%3D%3D

Expected behavior

Class decorators + keepClassNames should work properly in compiled code.

Works in tsc:

❯ tsc
❯ node index.js
class extends Base {
            constructor() {
                super(...arguments);
                this.prop = 100;
            }
        }
ClassX { prop: 100 }
class prop: 100

Actual behavior

❯ npx swc index.ts -o index.js
Successfully compiled 1 file with swc.
❯ node index.js
class ClassX {
    static checkX() {
        console.log(String(ClassX));
        console.log(new ClassX());
        // @ts-ignore
        console.log('class prop:', new ClassX().prop);
    }
}
ClassX {}
class prop: undefined

Version

1.3.19

Additional context

This issue affects all devs using ts-node + swc, with target >=es2015, and also @swc-node/register, as they do not provide a way to disable keepClassNames (they ignore .swcrc file and instead transform tsconfig.json to a set of options passed directly to swc, together with swcrc: false) But still, if there was an option to disable keepClassNames, it could then break i.a. TypeORM which requires it to be enabled. (related: TypeStrong/ts-node#1343)

More tests:

Works when keepClassNames: false but of course original class name is then altered.

❯ npx swc index.ts -o index2.js
Successfully compiled 1 file with swc.
❯ node index2.js
class extends Base {
            constructor(...args){
                super(...args);
                this.prop = 100;
            }
        }
ClassX1 { prop: 100 }
class prop: 100

difference in compiled code for swc + keepClassNames:true (non-working) vs swc + keepClassNames:false (working, but)

@@ -14,7 +14,7 @@ function CommonProp() {
         };
     };
 }
-let ClassX = class ClassX {
+let ClassX = class ClassX1 {
     static checkX() {
         console.log(String(ClassX));
         console.log(new ClassX());

difference between swc + keepClassNames:true (non-working) vs tsc (working) (ignoring formatting differences, I ran prettier on both outputs)

+'use strict';
 var __decorate =
   (this && this.__decorate) ||
   function (decorators, target, key, desc) {
@@ -17,23 +18,24 @@ var __decorate =
           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;
   };
+var ClassX_1;
 function CommonProp() {
   return (Base) => {
     return class extends Base {
-      constructor(...args) {
-        super(...args);
+      constructor() {
+        super(...arguments);
         this.prop = 100;
       }
     };
   };
 }
-let ClassX = class ClassX {
+let ClassX = (ClassX_1 = class ClassX {
   static checkX() {
-    console.log(String(ClassX));
-    console.log(new ClassX());
+    console.log(String(ClassX_1));
+    console.log(new ClassX_1());
     // @ts-ignore
-    console.log('class prop:', new ClassX().prop);
+    console.log('class prop:', new ClassX_1().prop);
   }
-};
-ClassX = __decorate([CommonProp()], ClassX);
+});
+ClassX = ClassX_1 = __decorate([CommonProp()], ClassX);
 ClassX.checkX();

Tested on node v16.4.2, win10.

Possibly also related to #5291