fix(tracer): avoid throwing errors in manual instrumentation when running outside of AWS Lambda

[dreamorosi]

Description of your changes

As reporded by @ijemmy during manual tests manually instrumenting a function with Tracer outside of AWS Lambda was throwing an error due to the lack of traces & context.

This was a bug since Tracer should automatically detect its running outside of Lambda and deactivate itself. The bug affected only manual instrumentation while the Middy middleware and Class decorator were unaffected.

Changes:

• Now leveraging the setContextMissingStrategy() method from the Node.js x-ray-sdk to disable throwing errors when tracing is disabled.
• Changed behaviour of Tracer.setSegment() & Tracer.getSegment() to respect value of Tracer. tracingEnabled
• Now Tracer.getSegment() returns a dummy segment when tracing is disabled
• Uniformed usage of Tracer.isTracingEnabled() over accessing attribute directly throughout class
• Added additional unit test cases to cover new behaviours

How to verify this change

Check that all checks are successful, OR:

1. Checkout branch locally
2. cd packages/tracing && npm run package
3. Init new project & install version packaged at previous step
4. Run the lambda below (in Javascript, no TS needed) & you should not see any error

const { Tracer } = require('@aws-lambda-powertools/tracer');

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

const handler = async (_event, context) => {
    const segment = tracer.getSegment(); // This is the facade segment (the one that is created by AWS Lambda)
    // Create subsegment for the function & set it as active
    const subsegment = segment.addNewSubsegment(`## ${process.env._HANDLER}`);
    tracer.setSegment(subsegment);

    // Annotate the subsegment with the cold start & serviceName
    tracer.annotateColdStart();
    tracer.addServiceNameAnnotation();

    let res;
    try {
        /* ... */
        // Add the response as metadata 
        tracer.addResponseAsMetadata(res, process.env._HANDLER);
    } catch (err) {
        // Add the error as metadata
        tracer.addErrorAsMetadata(err);
        throw err;
    } finally {
        // Close subsegment (the AWS Lambda one is closed automatically)
        subsegment.close();
        // Set back the facade segment as active again
        tracer.setSegment(segment);
    }
    console.log('ALL GOOD');
    return res;
};

handler();

Related issues, RFCs

N/A

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published in downstream module
• The PR title follows the conventional commit semantics

Breaking change checklist

N/A

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[flochaz]

LGTM

[saragerion]

Left some minor comments but already looks good