Fixed the equality contract on Metrics type

[YohDeadfall]

HashSet<T> doesn't override GetHashCode. Therefore, the default provided algorithm for reference types is used which doesn't take fields into account as it happens for value types. That breaks the equality contracts on Metrics.

Ideally HashCode type should be used for more correct computations with less number of collisions, but that requires increasing the minimal target framework.

SetEqual is available since .NET Fx 3.5 and is destined for equality comparison of two different hash set instances. Since both instances of the Metrics type has the same default comparer, the method works as a sugar over a length check followed by iteration over one set and probing the second one for containing the current element through the Contains method.

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[technige]

Thank you for your submission. We will review this in due course as and when someone is available on the team to do so.

[flobernd]

Thanks as well for this contribution!

It might be worth adding a conditional reference to Microsoft.Bcl.HashCode for the net462 and netstandard2.0 targets. There are around ~150 custom GetHashCode implementations in the project (a lot of them are auto-generated) that could benefit from using HashCode. I will check internally, if this is something we might consider.

For now I'm going to approve the PR to have this fix included in the next patch release. The HashCode optimization can be done later.