add fiber ref for disabling the tracer (#2381)

.changeset/hip-bags-smell.md

@@ -0,0 +1,17 @@
+---
+"effect": patch
+---
+
+add fiber ref for disabling the tracer
+
+You can use it with the Effect.withTracerEnabled api:
+
+```ts
+import { Effect } from "effect";
+
+Effect.succeed(42).pipe(
+  Effect.withSpan("my-span"),
+  // the span will not be registered with the tracer
+  Effect.withTracerEnabled(false),
+);
+```

packages/effect/src/Effect.ts

@@ -5061,6 +5061,25 @@ export const withTracer: {
 export const withTracerScoped: (value: Tracer.Tracer) => Effect<void, never, Scope.Scope> =
   fiberRuntime.withTracerScoped
 
+/**
+ * Disable the tracer for the given Effect.
+ *
+ * @since 2.0.0
+ * @category tracing
+ * @example
+ * import { Effect } from "effect"
+ *
+ * Effect.succeed(42).pipe(
+ *   Effect.withSpan("my-span"),
+ *   // the span will not be registered with the tracer
+ *   Effect.withTracerEnabled(false)
+ * )
+ */
+export const withTracerEnabled: {
+  (enabled: boolean): <A, E, R>(effect: Effect<A, E, R>) => Effect<A, E, R>
+  <A, E, R>(effect: Effect<A, E, R>, enabled: boolean): Effect<A, E, R>
+} = core.withTracerEnabled
+
 /**
  * @since 2.0.0
  * @category tracing

packages/effect/src/FiberRef.ts

@@ -373,6 +373,12 @@ export const currentSupervisor: FiberRef<Supervisor.Supervisor<any>> = fiberRunt
  */
 export const currentMetricLabels: FiberRef<ReadonlyArray<MetricLabel.MetricLabel>> = core.currentMetricLabels
 
+/**
+ * @since 2.0.0
+ * @category fiberRefs
+ */
+export const currentTracerEnabled: FiberRef<boolean> = core.currentTracerEnabled
+
 /**
  * @since 2.0.0
  * @category fiberRefs

packages/effect/src/Layer.ts

@@ -979,6 +979,15 @@ export const span: (
  */
 export const setTracer: (tracer: Tracer.Tracer) => Layer<never> = circularLayer.setTracer
 
+/**
+ * @since 2.0.0
+ * @category tracing
+ */
+export const setTracerEnabled: (enabled: boolean) => Layer<never> = (enabled: boolean) =>
+  scopedDiscard(
+    fiberRuntime.fiberRefLocallyScoped(core.currentTracerEnabled, enabled)
+  )
+
 /**
  * @since 2.0.0
  * @category tracing

packages/effect/src/internal/core-effect.ts

@@ -2051,6 +2051,11 @@ export const makeSpan = (
 ): Effect.Effect<Tracer.Span> =>
   core.flatMap(fiberRefs, (fiberRefs) =>
     core.sync(() => {
+      const enabled = FiberRefs.getOrDefault(fiberRefs, core.currentTracerEnabled)
+      if (enabled === false) {
+        return core.noopSpan
+      }
+
       const context = FiberRefs.getOrDefault(fiberRefs, core.currentContext)
       const services = FiberRefs.getOrDefault(fiberRefs, defaultServices.currentServices)
 
@@ -2131,10 +2136,12 @@ export const useSpan: {
     makeSpan(name, options),
     evaluate,
     (span, exit) =>
-      core.flatMap(
-        currentTimeNanosTracing,
-        (endTime) => core.sync(() => span.end(endTime, exit))
-      )
+      span.status._tag === "Ended" ?
+        core.unit :
+        core.flatMap(
+          currentTimeNanosTracing,
+          (endTime) => core.sync(() => span.end(endTime, exit))
+        )
   )
 }
 

packages/effect/src/internal/core.ts

@@ -1372,6 +1372,17 @@ export const withRuntimeFlags = dual<
   return effect
 })
 
+/** @internal */
+export const withTracerEnabled = dual<
+  (enabled: boolean) => <A, E, R>(effect: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R>,
+  <A, E, R>(effect: Effect.Effect<A, E, R>, enabled: boolean) => Effect.Effect<A, E, R>
+>(2, (effect, enabled) =>
+  fiberRefLocally(
+    effect,
+    currentTracerEnabled,
+    enabled
+  ))
+
 /** @internal */
 export const withTracerTiming = dual<
   (enabled: boolean) => <A, E, R>(effect: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R>,
@@ -2015,6 +2026,12 @@ export const currentInterruptedCause: FiberRef.FiberRef<Cause.Cause<never>> = gl
     })
 )
 
+/** @internal */
+export const currentTracerEnabled: FiberRef.FiberRef<boolean> = globalValue(
+  Symbol.for("effect/FiberRef/currentTracerEnabled"),
+  () => fiberRefUnsafeMake(true)
+)
+
 /** @internal */
 export const currentTracerTimingEnabled: FiberRef.FiberRef<boolean> = globalValue(
   Symbol.for("effect/FiberRef/currentTracerTiming"),
@@ -3073,3 +3090,25 @@ export const currentSpanFromFiber = <A, E>(fiber: Fiber.RuntimeFiber<A, E>): Opt
     | undefined
   return span !== undefined && span._tag === "Span" ? Option.some(span) : Option.none()
 }
+
+/** @internal */
+export const noopSpan: Tracer.Span = globalValue("effect/Tracer/noopSpan", () => ({
+  _tag: "Span",
+  spanId: "noop",
+  traceId: "noop",
+  name: "noop",
+  sampled: false,
+  parent: Option.none(),
+  context: Context.empty(),
+  status: {
+    _tag: "Ended",
+    startTime: BigInt(0),
+    endTime: BigInt(0),
+    exit: exitUnit
+  },
+  attributes: new Map(),
+  links: [],
+  attribute() {},
+  event() {},
+  end() {}
+}))

packages/effect/src/internal/fiberRuntime.ts

@@ -3505,10 +3505,12 @@ export const makeSpanScoped = (
   acquireRelease(
     internalEffect.makeSpan(name, options),
     (span, exit) =>
-      core.flatMap(
-        internalEffect.currentTimeNanosTracing,
-        (endTime) => core.sync(() => span.end(endTime, exit))
-      )
+      span.status._tag === "Ended" ?
+        core.unit :
+        core.flatMap(
+          internalEffect.currentTimeNanosTracing,
+          (endTime) => core.sync(() => span.end(endTime, exit))
+        )
   )
 
 /* @internal */

packages/effect/src/internal/tracer.ts

@@ -59,7 +59,7 @@ export class NativeSpan implements Tracer.Span {
     this.spanId = `span${randomString(16)}`
   }
 
-  end = (endTime: bigint, exit: Exit.Exit<unknown, unknown>): void => {
+  end(endTime: bigint, exit: Exit.Exit<unknown, unknown>): void {
     this.status = {
       _tag: "Ended",
       endTime,
@@ -68,11 +68,11 @@ export class NativeSpan implements Tracer.Span {
     }
   }
 
-  attribute = (key: string, value: unknown): void => {
+  attribute(key: string, value: unknown): void {
     this.attributes.set(key, value)
   }
 
-  event = (name: string, startTime: bigint, attributes?: Record<string, unknown>): void => {
+  event(name: string, startTime: bigint, attributes?: Record<string, unknown>): void {
     this.events.push([name, startTime, attributes ?? {}])
   }
 }

packages/effect/test/Tracer.test.ts

@@ -258,4 +258,21 @@ describe("Tracer", () => {
         assert.strictEqual(onEndCalled, true)
       }))
   })
+
+  it.effect("withTracerEnabled", () =>
+    Effect.gen(function*($) {
+      const span = yield* $(
+        Effect.currentSpan,
+        Effect.withSpan("A"),
+        Effect.withTracerEnabled(false)
+      )
+      const spanB = yield* $(
+        Effect.currentSpan,
+        Effect.withSpan("B"),
+        Effect.withTracerEnabled(true)
+      )
+
+      assert.deepEqual(span.name, "noop")
+      assert.deepEqual(spanB.name, "B")
+    }))
 })