Function metrics_provider 

pub fn metrics_provider(
    endpoint: Option<String>,
    resource_detectors: Vec<Box<dyn ResourceDetector>>,
    histogram_buckets: Vec<HistogramBuckets>,
) -> Result<SdkMeterProvider>

Builds an SdkMeterProvider configured to export to an OTLP collector.

Aside from endpoint, it pulls OTEL configuration from the environment based on the variables defined here and here.

endpoint overrides the collector endpoint the environment would otherwise select (via OTEL_EXPORTER_OTLP_ENDPOINT/OTEL_EXPORTER_OTLP_METRICS_ENDPOINT), for callers that take their own explicit configuration (e.g. a CLI flag) rather than expecting operators to set OTel’s environment variables directly. Pass None to use the environment as normal.

resource_detectors lets the caller contribute additional resource attributes. They run before this crate’s own detectors, which set fields from OTEL_RESOURCE_ATTRIBUTES and telemetry.sdk{name, language, version}.

The caller is responsible for registering the returned provider as the global one (e.g. via opentelemetry::global::set_meter_provider). Instruments created by the macros in this module (e.g. counter) bind to whatever meter provider is global at the time they’re first used, and never rebind afterwards.

Exposed publicly so embedders that manage their own tracing::Subscriber (and so can’t call crate::init, which also installs one) can still set up Spin’s metrics: build a provider with this function and register it themselves, alongside their own, via opentelemetry::global::set_meter_provider.