Histograms don't support negative values, but should.

[kentquirk]

I am trying to create an exponential histogram containing negative values.

When I do so, I get [Record amount must be non-negative on Histogram](https://github.com/open-telemetry/opentelemetry-python/blob/8378db984edbc2a0532c5316e82df1ac649ba227/opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/instrument.py#L206) -- but as far as I can tell, the spec permits negative values on histograms and explicitly calls out negative value support for Exponential ones (the datatype even includes a collection of buckets called "Negative").

A search of issues and PRs didn't turn up a reason this was excluded. Is there one?

(I've now checked this with .NET and JS, and both of them also exclude negative values. I'm guessing this was added to the spec recently.)

[aabmass]

This is true for the data model, it can support negative values. However the spec says that Histogram instruments can only record non-negative values:

The value is expected to be non-negative. This API SHOULD be documented in a way to communicate to users that this value is expected to be non-negative. This API SHOULD NOT validate this value, that is left to implementations of the API.

the SDK is an implementation of the API so emits this warning. I couldn't find an issue for this exactly but some related discussion in open-telemetry/opentelemetry-specification#2757. I'd recommend opening a spec issue about this.

[kentquirk]

Thanks for the information. I will follow up on the spec side.

[ocelotl]

Closing for the time being, @kentquirk please reopen if necessary after getting input from the spec.