feat(trace): impl ShouldSample for Box<dyn ShouldSample>

[Oliboy50]

Fixes #
Design discussion issue (if applicable) #

Changes

Implement ShouldSample for Box<dyn ShouldSample> because:

• users of this crate cannot do it themselves (because of the Rust orphan rule)
• while working on a small wrapper around opentelemetry-sdk but tracer_provider_builder.with_sampler(...) currently only accepts a T: crate::trace::ShouldSample + 'static generic parameter... but I can't introduce generic types in my wrapper (for some reasons) and therefore I would like to use a dyn ShouldSample instead... and I currently can't do that

I'll update this PR to fix the "Merge requirement checklist" below, only if you are OK with it in the first place.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

• ✅login: Oliboy50 / (e648455)

The committers listed above are authorized under a signed CLA.

[utpilla]

Changes

Implement ShouldSample for Box<dyn ShouldSample> because:

• users of this crate cannot do it themselves (because of the Rust orphan rule)
• while working on a small wrapper around opentelemetry-sdk but tracer_provider_builder.with_sampler(...) currently only accepts a T: crate::trace::ShouldSample + 'static generic parameter... but I can't introduce generic types in my wrapper (for some reasons) and therefore I would like to use a dyn ShouldSample instead... and I currently can't do that

If I understand the issue correctly, your wrapper version of with_sampler method can only take trait objects and not impl traits.
If that's the case, could you use a wrapper struct to get around this issue? Something like this:

fn with_sampler_custom(sampler: Box<dyn ShouldSample>) -> opentelemetry_sdk::trace::Builder {
    opentelemetry_sdk::trace::TracerProvider::builder().with_sampler(WrapperSampler(sampler))
}

#[derive(Debug, Clone)]
struct WrapperSampler(Box<dyn ShouldSample>);

impl ShouldSample for WrapperSampler {
    fn should_sample(
        &self,
        parent_context: Option<&Context>,
        trace_id: opentelemetry::trace::TraceId,
        name: &str,
        span_kind: &SpanKind,
        attributes: &[KeyValue],
        links: &[opentelemetry::trace::Link],
    ) -> opentelemetry::trace::SamplingResult {
        let sampler = self.0.as_ref();
        let result =
            sampler.should_sample(parent_context, trace_id, name, span_kind, attributes, links);
        result
    }
}

[Oliboy50]

@utpilla you are right, I don't know why I didn't think about using the NewType pattern to get around the orphan rule 🤦

I close my PR then, thank you for your help ❤️