[pkg/ottl] Allow indexing any slice type

[TylerHelmuth]

I was just shown the scenario

set(resource.attributes["my.environment.2"], Split(resource.attributes["host.name"],"-")[1])

that produces an error:

{"kind": "processor", "name": "transform", "pipeline": "logs", "error": "type, []string, does not support int indexing", "statement": "set(resource.attributes[\"my.environment.2\"], Split(resource.attributes[\"host.name\"],\"-\")[1])"}

Although the language does support indexing the return value of the Converter, it only supports indexing pcommon.Slice and []any, but Split returns a []string. We need to make indexing slices more generic. This might need to be its own issue. Related code:

opentelemetry-collector-contrib/pkg/ottl/expression.go

Lines 98 to 112 in 60430e1

	case k.Int != nil:
	switch r := result.(type) {
	case pcommon.Slice:
	if int(*k.Int) >= r.Len() || int(*k.Int) < 0 {
	return nil, fmt.Errorf("index %v out of bounds", *k.Int)
	}
	result = ottlcommon.GetValue(r.At(int(*k.Int)))
	case []any:
	if int(*k.Int) >= len(r) || int(*k.Int) < 0 {
	return nil, fmt.Errorf("index %v out of bounds", *k.Int)
	}
	result = r[*k.Int]
	default:
	return nil, fmt.Errorf("type, %T, does not support int indexing", result)
	}

Originally posted by @TylerHelmuth in #26108 (comment)

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[SplitThePotCyrus]

Yes please, fix for this would be great.

I've been trying to figure out this issue for a half a day, until I found this just now. 😓
Now I have to figure out how to accomplish what I need in a different way.

[TylerHelmuth]

The workaround for this issue is to use cache. set(resource.attributes["my.environment.2"], Split(resource.attributes["host.name"],"-")[1]) becomes:

set(cache["temp"], Split(resource.attributes["host.name"],"-"))
set(resource.attributes["my.environment.2"], cache["temp"][1])

[github-actions]

This issue has been inactive for 60 days. It will be closed in 60 days if there is no activity. To ping code owners by adding a component label, see Adding Labels via Comments, or if you are unsure of which component this issue relates to, please ping @open-telemetry/collector-contrib-triagers. If this issue is still relevant, please ping the code owners or leave a comment explaining why it is still relevant. Otherwise, please close it.

Pinging code owners:

• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley

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[github-actions]

This issue has been inactive for 60 days. It will be closed in 60 days if there is no activity. To ping code owners by adding a component label, see Adding Labels via Comments, or if you are unsure of which component this issue relates to, please ping @open-telemetry/collector-contrib-triagers. If this issue is still relevant, please ping the code owners or leave a comment explaining why it is still relevant. Otherwise, please close it.

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[evan-bradley]

At a minimum, we should achieve type coverage for all types that OTTL supports. If possible, a generic solution would be nice, assuming we can do this with either reflection or some creative type casting.