Bug: @tracer.captureMethod() is not bound to the decorated class

[ratscrew]

Bug description

The @tracer.captureMethod() decorator is bound to the decorator not the class its decorating.

export class Lambda implements LambdaInterface {
   @tracer.captureMethod()
   myMethod(){

      //other method is undefined as "this" is no longer the Lambda class
      this.otherMethod()
   }

   otherMethod(){}
}

Expected Behavior

this.otherMethod() should call the this.otherMethod() in the same class

Current Behavior

this.otherMethod() is undefined

Possible Solution

see #1026
the @tracer.captureLambdaHandler() decorator already does this

Steps to Reproduce

1. create a class with two or methods in it
2. add the decorator @tracer.captureMethod() to one or more of the function
3. call another method or prop in the decorated method
4. the method or prop will be undefined

Environment

• Powertools version used: 1.0.2
• Packaging format (Layers, npm):
• AWS Lambda function runtime:
• Debugging logs:

Related issues, RFCs

#1026

[dreamorosi]

Thank you for opening the issue, appreciate your time.

I was able to reproduce the bug described using this code:

import { Tracer } from "@aws-lambda-powertools/tracer";
import { LambdaInterface } from "@aws-lambda-powertools/commons";

const tracer = new Tracer();

export class Lambda implements LambdaInterface {
  @tracer.captureMethod()
  myMethod() {
    //other method is undefined as "this" is no longer the Lambda class
    this.otherMethod();
  }

  otherMethod() {
    console.log("other method");
  }

  @tracer.captureLambdaHandler()
  public async handler(_event: any, _context: any): Promise<void> {
    this.myMethod();
  }
}

export const handlerClass = new Lambda();
export const handler = handlerClass.handler;

Given that you have already opened a PR to fix this I'm gonna assign the issue to you.

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[misterjoshua]

@dreamorosi Hey. I tested @tracer.captureMethod() in the recently released v1.1.0. Although #1026 was included, I don't believe this issue was successfully fixed. Here is an example of code that does not work:

import { Tracer } from '@aws-lambda-powertools/tracer';

test('bug', async () => {
  const tracer = new Tracer();

  class BugClass {
    constructor(private readonly callback: () => string) {}

    @tracer.captureMethod()
    async getFoo(): Promise<string> {
      return this.callback();
    }
  }

  const myClass = new BugClass(() => 'somevalue');
  await expect(myClass.getFoo()).resolves.toEqual('somevalue');
});

Here is a screenshot demonstrating the unexpected error:

And here is a file from a repository that can reproduce the issue:
https://github.com/misterjoshua/lpt-tracer-bug/blob/main/test/bug.test.ts

You can test this for yourself by typing the following:

git clone https://github.com/misterjoshua/lpt-tracer-bug.git
cd lpt-tracer-bug
yarn install
yarn test

[dreamorosi]

After looking into it a bit more it seems that the issue is not anymore related to how this is bound but instead to readonly attributes/methods of the decorated class.

For instance, the example below works as expected:

import { Tracer } from "@aws-lambda-powertools/tracer";
import { LambdaInterface } from "@aws-lambda-powertools/commons";

const tracer = new Tracer({ serviceName: "serverlessAirline" });

class BugClass {
  constructor() {}

  private ok(): void {
    console.log("HELLO");
    return;
  }

  @tracer.captureMethod()
  async getFoo(): Promise<void> {
    return this.ok();
  }
}

class Lambda implements LambdaInterface {
  @tracer.captureMethod()
  // eslint-disable-next-line @typescript-eslint/ban-ts-comment
  // @ts-ignore
  public async dummyMethod(): Promise<string> {
    return `otherMethod:${this.otherMethod()}`;
  }

  @tracer.captureLambdaHandler()
  public async handler(_event: any, _context: any): Promise<string> {
    const bugClass = new BugClass();
    await bugClass.getFoo();

    return await this.dummyMethod();
  }

  public otherMethod(): string {
    return "otherMethod";
  }
}

export const myFunction = new Lambda();
export const handler = myFunction.handler;

To be honest I'm not sure if this is an expected behavior in TS decorators, I'd have to investigate more. But definitely I would consider this a separate issue from the first one that you reported - which was very valid and that was fixed.

[dreamorosi]

Closing this in favor of #1056

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