feat: change the sampler's signature for better decisions

src/async.ts

@@ -12,7 +12,7 @@ import { span_buffer, wait_promises } from './_internal';
 export { configure, report } from './_internal';
 
 type API = {
- sampler: Sampler | boolean;
+ sampler: typeof Sampler | boolean;
  scope: { name: string };
  clock: ClockLike;
 };
@@ -40,8 +40,9 @@ export function span(name: string, parent_id?: Traceparent | string) {
  const parent = (typeof parent_id === 'string' ? tctx.parse(parent_id) : (parent_id || current_span?.traceparent));
  const id = parent?.child() || tctx.make();
 
- const is_sampling = typeof should_sample == 'boolean' ? should_sample : should_sample(name, id, scope);
- !is_sampling ? tctx.unsample(id) : tctx.sample(id);
+ const is_sampling = typeof should_sample == 'boolean' ? should_sample : should_sample(id.parent_id, parent, name, scope);
+ if (is_sampling) tctx.sample(id);
+ else tctx.unsample(id);
 
  const span_obj: Span = {
  id, parent, name,

src/index.d.ts

@@ -27,7 +27,7 @@ export type Options = {
  /**
  * @borrows {@link Sampler}
  */
- sampler?: Sampler | boolean;
+ sampler?: typeof Sampler | boolean;
 
  clock?: ClockLike;
 };
@@ -47,20 +47,24 @@ export type Context = {
  * Return true if the span should be sampled, and reported to the {@link Exporter}.
  * Return false if the span should not be sampled, and not reported to the {@link Exporter}.
  */
-export type Sampler = (
+export function Sampler(
  /**
- * The name of the span.
+ * The id of the new span looking for a sampling decision.
+ */
+ id: string,
+ /**
+ * The traceparent of the new span looking for a sampling decision.
  */
- name: string,
+ parent: Traceparent | undefined,
  /**
- * The traceparent id of the span.
+ * The name of the span.
  */
- id: Traceparent,
+ name: string,
  /**
  * The tracer this span belongs to.
  */
  tracer: { readonly name: string },
-) => boolean;
+): boolean;
 
 // --- spans
 

src/index.ts

@@ -24,8 +24,9 @@ export function tracer(name: string, options?: Options): Tracer {
  const parent = (typeof parent_id === 'string' ? tctx.parse(parent_id) : parent_id);
  const id = parent?.child() || tctx.make();
 
- const is_sampling = typeof should_sample == 'boolean' ? should_sample : should_sample(name, id, scope);
- !is_sampling ? tctx.unsample(id) : tctx.sample(id);
+ const is_sampling = typeof should_sample == 'boolean' ? should_sample : should_sample(id.parent_id, parent, name, scope);
+ if (is_sampling) tctx.sample(id);
+ else tctx.unsample(id);
 
  const span_obj: Span = {
  id, parent, name,