[sdk-*] remove mergeResourceWithDefaults option and align resource merging behavior with spec

[pichlermarc]

Description

Our previous implementation of resource merging in SDKs was not compliant with the specification, which states that:

The SDK MUST provide access to a Resource with at least the attributes listed at
Semantic Attributes with SDK-provided Default Value.
This resource MUST be associated with a TracerProvider or MeterProvider
if another resource was not explicitly specified.

Our implementation always merged the default resource, regardless of the user supplying their own so there was no way to set an empty resource explicitly. Since simply changing the behavior would've broken too many users that rely on the non-secification compliant behavior, we opted to add a flag (mergeResourceWithDefaults in #4617) that would allow users to opt-in to the specification compliant behavior instead.

The goal of this issue is to remove the option from all SDKs (and sdk-node) AND align the behavior with the specification (meaning: only merging when the user does NOT provide a resource)

This issue is considered done when:

• mergeResourceWithDefaults has been removed in @opentelemetry/sdk-logs and the behavior has been aligned with the specification
  • see

    opentelemetry-js/experimental/packages/sdk-logs/src/LoggerProvider.ts

    Lines 31 to 41 in 012dc9e

    	function prepareResource(
    	mergeWithDefaults: boolean,
    	providedResource: Resource | undefined
    	) {
    	const resource = providedResource ?? Resource.empty();
    	if (mergeWithDefaults) {
    	return Resource.default().merge(resource);
    	}
    	return resource;
    	}

  • see

    opentelemetry-js/experimental/packages/sdk-logs/src/types.ts

    Line 36 in 8483b68

    mergeResourceWithDefaults?: boolean;

• mergeResourceWithDefaults has been removed in @opentelemetry/sdk-metrics and the behavior has been aligned with the specification
  • see

    opentelemetry-js/packages/sdk-metrics/src/MeterProvider.ts

    Lines 50 to 60 in 012dc9e

    	function prepareResource(
    	mergeWithDefaults: boolean,
    	providedResource: Resource | undefined
    	) {
    	const resource = providedResource ?? Resource.empty();
    	if (mergeWithDefaults) {
    	return Resource.default().merge(resource);
    	}
    	return resource;
    	}

  • see

    opentelemetry-js/packages/sdk-metrics/src/MeterProvider.ts

    Line 43 in 012dc9e

    mergeResourceWithDefaults?: boolean;

• mergeResourceWithDefaults has been removed in @opentelemetry/sdk-traces and the behavior has been aligned with the specification
  • see

    opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/BasicTracerProvider.ts

    Lines 84 to 86 in 012dc9e

    	if (mergedConfig.mergeResourceWithDefaults) {
    	this.resource = Resource.default().merge(this.resource);
    	}

  • see

    opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/config.ts

    Line 57 in 012dc9e

    mergeResourceWithDefaults: true,

  • see

    opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/types.ts

    Line 41 in 8483b68

    mergeResourceWithDefaults?: boolean;

• mergeResourceWithDefaults has been removed in @opentelemetry/sdk-node and the behavior has been aligned with the specification
  • see

    opentelemetry-js/experimental/packages/opentelemetry-sdk-node/src/sdk.ts

    Line 99 in 012dc9e

    private _mergeResourceWithDefaults: boolean;

  • see

    opentelemetry-js/experimental/packages/opentelemetry-sdk-node/src/types.ts

    Line 43 in 012dc9e

    mergeResourceWithDefaults?: boolean;

Additional requirements

• Make sure to adjust tests and remove tests that are not needed anymore

Additional context

• feat(resources): implements service.instance.id #4608 (comment) was the first time we noticed that the behvavior is not spec compliant
• feat(sdk-*): add option to opt-out from merging the resource with Resource.default() #4617 initially added the option that should be removed
• @opentelemetry/sdk-trace-base - Avoid merging Resource Attributes by default on BasicTracerProvider #4930 requested a way to do this previously

[david-luna]

I'm working on a PR for this one :)