Derive Macro Metrics 

#[derive(Metrics)]
{
    // Attributes available to this derive:
    #[new]
    #[crate_path]
    #[config]
    #[raw_end_fn]
    #[calculate]
    #[hidden]
}

Derive macros for Metrics trait.

Using this macro will emit implementation of Metrics and Default traits, and some helper assertions.

By default each metric field is initialized using Default::default() implementation. But one can customize constructor by using #[new(...)] attribute, where they can provide arguments for new method in the metric type.

In example below, cycles field will be initialized with PerfEventMetric::new(perf_event::events::Hardware::CPU_CYCLES).

Example:

#[derive(Metrics)]
pub struct MetricsProvider {
   /// Without `#[new]` attribute, the metric will be initialized with `Default::default()`.
   /// wall_time can be gathered from Instant or from perf_event(CPU_CLOCK), result is similar,
   /// but Instant is more portable.
   pub wall_time: crate::InstantProvider,
   /// CPU cycles spent in the span.
   /// The first metric in the list will be used as the primary metric and adds report of %parent in the report.
   #[new(perf_event::events::Hardware::CPU_CYCLES)]
   pub cycles: crate::PerfEventMetric,
}

Macro is only applies to structs where each member implements the SingleMetric trait.

Note: Metrics and SingleMetric are different traits.

#[config] attribute allows to customize display options for each metric, see [MetricReportInfo] for more details.

Example:

#[derive(Metrics)]
pub struct MetricsProvider {
    #[new(perf_event::events::Hardware::CPU_CYCLES)]
    #[config(show_spread = false)]
    pub cycles: crate::PerfEventMetric,
}