Why are data fetchers returning CompletionStage or CompletableFuture not enabled for instrumentation by default?

[arichardson175]

Our team recently noticed some data fetchers returning CompletableFuture types were not emitting metrics like gql.resolver.95percentile, and came across the following code in DgsSchemaProvider:

val enableInstrumentation =
    if (method.isAnnotationPresent(DgsEnableDataFetcherInstrumentation::class.java)) {
        val dgsEnableDataFetcherInstrumentation =
            method.getAnnotation(DgsEnableDataFetcherInstrumentation::class.java)
        dgsEnableDataFetcherInstrumentation.value
    } else {
        method.returnType != CompletionStage::class.java && method.returnType != CompletableFuture::class.java
    }

We were able to get the metrics back by explicitly adding @DgsEnableDataFetcherInstrumentation to our data fetchers, but were wondering: why are metrics disabled by default for these return types? Is there anything we should watch out for when using @DgsEnableDataFetcherInstrumentation here?