fix(idempotency): preserve scope of decorated class

[dreamorosi]

Summary

Changes

Please provide a summary of what's being changed

This PR addresses the bug in the linked issue that caused class methods decorated with the @idempotent decorator to lose the original scope of the class.

In simpler terms, when working with classes it's common to reference other class methods or properties. In JavaScript this is done via the this keyword, which in the case of classes is bound to the class instance.

For example, in the code snippet below the handler method is able to access the logger property by using the this keyword, which at runtime is bound to the fooInstance instance.

export class Foo {
    private readonly logger = console;

    public async handler(event: unknown): Promise<string> {
        this.logger.debug('Received event');

        return 'success';
    }
}

const fooInstance = new Foo();

When working with class method decorators in TypeScript it's important to keep in mind that the decorator replaces the method implementation with one it defines. In doing so, it's important to pass down the original scope so that the decorated method maintains access to the this scope.

This PR makes changes to the makeIdempotent function, the IdempotencyHandler class, and the idempotent decorator implementation so that this happens.

Specifically, the PR:

• converts the makeIdempotent function from an arrow function to a regular function so that it maintains a binding to this
• modifies the idempotent decorator to explicitly .bind(this) on the makeIdempotent function when replacing the implementation of the decorated method
• updates the IdempotencyHandler to now accept a new thisArg parameter and restore it onto the original function when calling it

I have also added a new unit test case and modified one of the integration test cases to confirm that the fix works.

Please add the issue number below, if no issue is present the PR might get blocked and not be reviewed

Issue number: closes #2692

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[dreamorosi]

Integration tests passing: https://github.com/aws-powertools/powertools-lambda-typescript/actions/runs/9679720071

[am29d]

Great catch and a quick PR with the fix, Thank you Andrea!

Thanks @HaaLeo for reporting the issue!