TypeScript decorators lose context values.

[ZQH123196]

What version of Bun is running?

1.2.15

What platform is your computer?

Microsoft Windows NT 10.0.26100.0 x64

What steps can reproduce the bug?

The decorator seems to lose context information.
When executing "bun xxx.ts" with decorators, it shows different results from "bun xxx.js" compiled by tsc.
note: "originalMethod" also gets the same problem.

my test code: tmp.zip

function loggedMethod(originalMethod: any, context: ClassMethodDecoratorContext) {
    const methodName = String(context.name);
    console.log(`🔍 自动日志装饰器应用于方法: ${methodName}`);
    function replacementMethod(this: any, ...args: any[]) {
        console.log(`LOG: Entering method '${methodName}'.`)
        const result = originalMethod.call(this, ...args);
        console.log(`LOG: Exiting method '${methodName}'.`)
        return result;
    }
    return replacementMethod;
}

class ExampleClass {
    @loggedMethod
    foo() {
        console.log("foo 方法执行完毕");
    }
}

new ExampleClass().foo();

What is the expected behavior?

Hope "bun xxx.ts" can correctly process decorator context values.

In ".ts" file, "methodName" should be log correctly like ".js" files.

What do you see instead?

Additional information

[liudonghua123]

[deanrih]

I want to add that it seems Bun didn't take the experimentalDecorators config on tsconfig.json into account (or perhaps just hasn't implemented the TC39 Stage 3 Decorator Proposal just yet?), so whether the value is true, false or just not being provided into the config, Bun's behaviour is as if the experimentalDecorators is true, regardless of the config. While the behaviour of the tsc transpiled code, TypeScript's Playground, and Deno, respect the config and behave the same.

Consider this code (more or less the same as above, but with some added code)

console.clear();

function loggedMethod<This, Args extends any[], Return>(
    target: (this: This, ...args: Args) => Return,
    context: ClassMethodDecoratorContext<This, (this: This, ...args: Args) => Return>
) {
    console.log(`>> Decorator`);
    const methodName = String(context.name);
    console.log("Target:");
    console.log(target);
    console.log("Context:");
    console.log(context);

    function replacementMethod(this: This, ...args: Args): Return {
        console.log(`LOG: Entering method '${methodName}'.`)
        const result = target.call(this, ...args);
        console.log(`LOG: Exiting method '${methodName}'.`)
        return result;
    }

    return replacementMethod;
}

function altLoggedMethod(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    console.log(`>> Experimental Decorator`);
    console.log("Target:");
    console.log(target);
    console.log("PropKey:");
    console.log(propertyKey);
    console.log("Desc:");
    console.log(descriptor);

    const originalMethod = descriptor.value;

    descriptor.value = function(...args: any[]) {
        console.log(`LOG: Entering method '${propertyKey}'.`)
        const result = originalMethod.call(this, ...args);
        console.log(`LOG: Exiting method '${propertyKey}'.`)
        return result;
    }
}

class Person {
    name: string;
    constructor(name: string) {
        this.name = name;
    }

    @loggedMethod
    greet_1() {
        console.log(`Hello, my name is ${this.name}.`);
    }

    @altLoggedMethod
    greet_2() {
        console.log(`Hello, my name is ${this.name}.`);
    }
}

const p = new Person("Ron");
p.greet_1();
p.greet_2();

And here's some result/log comparison

TypeScript Playground ("experimentalDecorators": false)

[LOG]: ">> Decorator" 
[LOG]: "Target:" 
[LOG]: greet_1() {
            console.log(`Hello, my name is ${this.name}.`);
        } 
[LOG]: "Context:" 
[LOG]: {
  "kind": "method",
  "name": "greet_1",
  "static": false,
  "private": false,
  "access": {},
  "metadata": undefined
} 
[LOG]: ">> Experimental Decorator" 
[LOG]: "Target:" 
[LOG]: greet_2() {
            console.log(`Hello, my name is ${this.name}.`);
        } 
[LOG]: "PropKey:" 
[LOG]: {
  "kind": "method",
  "name": "greet_2",
  "static": false,
  "private": false,
  "access": {},
  "metadata": undefined
} 
[LOG]: "Desc:" 
[LOG]: undefined 
[ERR]: "Executed JavaScript Failed:" 
[ERR]: Cannot read properties of undefined (reading 'value') 

# IF THE @altLoggerMethod is removed ===========================
[LOG]: ">> Decorator" 
[LOG]: "Target:" 
[LOG]: greet_1() {
            console.log(`Hello, my name is ${this.name}.`);
        } 
[LOG]: "Context:" 
[LOG]: {
  "kind": "method",
  "name": "greet_1",
  "static": false,
  "private": false,
  "access": {},
  "metadata": undefined
} 
[LOG]: "LOG: Entering method 'greet_1'." 
[LOG]: "Hello, my name is Ron." 
[LOG]: "LOG: Exiting method 'greet_1'." 
[LOG]: "Hello, my name is Ron." 

TypeScript Playground ("experimentalDecorators": true)

[LOG]: ">> Decorator" 
[LOG]: "Target:" 
[LOG]: Person: {} 
[LOG]: "Context:" 
[LOG]: "greet_1" 
[LOG]: ">> Experimental Decorator" 
[LOG]: "Target:" 
[LOG]: Person: {} 
[LOG]: "PropKey:" 
[LOG]: "greet_2" 
[LOG]: "Desc:" 
[LOG]: {
  "writable": true,
  "enumerable": false,
  "configurable": true
} 
[LOG]: "Hello, my name is Ron." 
[LOG]: "LOG: Entering method 'greet_2'." 
[LOG]: "Hello, my name is Ron." 
[LOG]: "LOG: Exiting method 'greet_2'." 

Deno ("experimentalDecorators": false)

>> Decorator
Target:
[Function: greet_1]
Context:
{
  kind: "method",
  name: "greet_1",
  static: false,
  private: false,
  metadata: [Object: null prototype] {},
  addInitializer: [Function: addInitializer],
  access: { get: [Function: get] }
}
>> Experimental Decorator
Target:
[Function: greet_2]
PropKey:
{
  kind: "method",
  name: "greet_2",
  static: false,
  private: false,
  metadata: [Object: null prototype] {},
  addInitializer: [Function: addInitializer],
  access: { get: [Function: get] }
}
Desc:
undefined
error: Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'value')
        const originalMethod = descriptor.value;

    at altLoggedMethod (file://<path>/src/decorator.ts:171:36)
    at memberDec (file://<path>/src/decorator.ts:130:29)
    at applyMemberDec (file://<path>/src/decorator.ts:130:29)
    at applyMemberDecs (file://<path>/src/decorator.ts:130:29)
    at applyDecs2203R (file://<path>/src/decorator.ts:130:29)
    at _apply_decs_2203_r (file://<path>/src/decorator.ts:130:29)
    at Person.<static_initializer> (file://<path>/src/decorator.ts:181:7)
    at file://<path>/src/decorator.ts:132:9

# IF THE @altLoggerMethod is removed ===========================
>> Decorator
Target:
[Function: greet_1]
Context:
{
  kind: "method",
  name: "greet_1",
  static: false,
  private: false,
  metadata: [Object: null prototype] {},
  addInitializer: [Function: addInitializer],
  access: { get: [Function: get] }
}
LOG: Entering method 'greet_1'.
Hello, my name is Ron.
LOG: Exiting method 'greet_1'.
Hello, my name is Ron.

Deno ("experimentalDecorators": true)

>> Decorator
Target:
{}
Context:
greet_1
>> Experimental Decorator
Target:
{}
PropKey:
greet_2
Desc:
{
  value: [Function: greet_2],
  writable: true,
  enumerable: false,
  configurable: true
}
Hello, my name is Ron.
LOG: Entering method 'greet_2'.
Hello, my name is Ron.
LOG: Exiting method 'greet_2'.

Bun ("experimentalDecorators": false)

>> Decorator
Target:
Person {
  greet_1: [Function: greet_1],
  greet_2: [Function: greet_2],
}
Context:
greet_1
>> Experimental Decorator
Target:
Person {
  greet_1: [Function: greet_1],
  greet_2: [Function: greet_2],
}
PropKey:
greet_2
Desc:
{
  value: [Function: greet_2],
  writable: true,
  enumerable: false,
  configurable: true,
}
Hello, my name is Ron.
LOG: Entering method 'greet_2'.
Hello, my name is Ron.
LOG: Exiting method 'greet_2'.

# IF THE @altLoggerMethod is removed ===========================
>> Decorator
Target:
Person {
  greet_1: [Function: greet_1],
  greet_2: [Function: greet_2],
}
Context:
greet_1
Hello, my name is Ron.
Hello, my name is Ron.

Bun ("experimentalDecorators": true)

>> Decorator
Target:
Person {
  greet_1: [Function: greet_1],
  greet_2: [Function: greet_2],
}
Context:
greet_1
>> Experimental Decorator
Target:
Person {
  greet_1: [Function: greet_1],
  greet_2: [Function: greet_2],
}
PropKey:
greet_2
Desc:
{
  value: [Function: greet_2],
  writable: true,
  enumerable: false,
  configurable: true,
}
Hello, my name is Ron.
LOG: Entering method 'greet_2'.
Hello, my name is Ron.
LOG: Exiting method 'greet_2'.

As you can see, in Bun's case, it does the exact same thing.

Tested on

TypeScript:
- 5.9.3
Deno:
- deno 2.5.6 (stable, release, x86_64-unknown-linux-gnu)
  v8 14.0.365.5-rusty
  typescript 5.9.2
Bun:
- 1.3.1

Playground URL:

https://www.typescriptlang.org/play/?target=99&jsx=0&experimentalDecorators=true#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-vqXJzhdLgard386azagSuQbigF23UebFRaoZap6GQDFwn6t5Guw+YyY2D9fvkfy+Nce2HUcUQPQCPi7Hs+wHMCAJfD1Jk+bdgH+RC3iAmcdwoRdilxQ1x2oYoKHoS5bSLZhjhw+c8KXeAADdbSIWA8FWWjd2KJiWNgY58QrcB0GdFl2y0bR9x5IEkKPL1xVPaVJzlDVg36GCN3gkdI31KTn2IpNzWOUjyPuaAqJtO0HUaZkAifN0oM9EV5LPP0lNDaiVTU9c4KHLTdR03SswTAyU1WdNSyQNIZBXPsoCrbkrHubYxwnK47PWVAiHIYp0CS2AUplehJN02o7geY48rs0tngAAQmBsqNWehiQ4AB9ABGLAuRjPTX09AAJWA7RAMRNnUag8uoYRqFVUq8q1KMqozKwAHoVuoGqazrRgWEa55mtgNqACYuoSqTvw+KZBuG0bxsm6bZqqMqI0WsLcAi14NhJCrYAAd2oGLUDir49HACCSXgA62s6lYIahshWpO3E1uoYUiDIEl0fsXA1px9bLCcyVFIDJt4DxqxrroW6JvK6bQbAMmUYJ71T19f16GU3YyaAA