Avoid eager read of the stack when captured by a span

.changeset/gorgeous-ties-tan.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Avoid eager read of the stack when captured by a span

packages/effect/src/Tracer.ts

@@ -5,6 +5,7 @@ import type * as Context from "./Context.js"
 import type * as Effect from "./Effect.js"
 import type * as Exit from "./Exit.js"
 import type * as Fiber from "./Fiber.js"
+import type { LazyArg } from "./Function.js"
 import * as defaultServices from "./internal/defaultServices.js"
 import * as internal from "./internal/tracer.js"
 import type * as Option from "./Option.js"
@@ -92,7 +93,7 @@ export interface SpanOptions {
   readonly root?: boolean | undefined
   readonly context?: Context.Context<never> | undefined
   readonly kind?: SpanKind | undefined
-  readonly captureStackTrace?: boolean | string | undefined
+  readonly captureStackTrace?: boolean | LazyArg<string | undefined> | undefined
 }
 
 /**

packages/effect/src/internal/cause.ts

@@ -5,6 +5,7 @@ import * as Either from "../Either.js"
 import * as Equal from "../Equal.js"
 import type * as FiberId from "../FiberId.js"
 import { constFalse, constTrue, dual, identity, pipe } from "../Function.js"
+import { globalValue } from "../GlobalValue.js"
 import * as Hash from "../Hash.js"
 import * as HashSet from "../HashSet.js"
 import { NodeInspectSymbol, toJSON } from "../Inspectable.js"
@@ -1052,6 +1053,9 @@ export const prettyErrorMessage = (u: unknown): string => {
 
 const locationRegex = /\((.*)\)/
 
+/** @internal */
+export const spanToTrace = globalValue("effect/Tracer/spanToTrace", () => new WeakMap())
+
 const prettyErrorStack = (message: string, stack: string, span?: Span | undefined): string => {
   const out: Array<string> = [message]
   const lines = stack.split("\n")
@@ -1072,8 +1076,9 @@ const prettyErrorStack = (message: string, stack: string, span?: Span | undefine
     let current: Span | AnySpan | undefined = span
     let i = 0
     while (current && current._tag === "Span" && i < 10) {
-      const stack = current.attributes.get("code.stacktrace")
-      if (typeof stack === "string") {
+      const stackFn = spanToTrace.get(current)
+      if (typeof stackFn === "function") {
+        const stack = stackFn()
         const locationMatch = stack.match(locationRegex)
         const location = locationMatch ? locationMatch[1] : stack.replace(/^at /, "")
         out.push(`    at ${current.name} (${location})`)

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

@@ -2054,8 +2054,8 @@ export const unsafeMakeSpan = <XA, XE>(
     options.kind ?? "internal"
   )
 
-  if (typeof options.captureStackTrace === "string") {
-    span.attribute("code.stacktrace", options.captureStackTrace)
+  if (typeof options.captureStackTrace === "function") {
+    internalCause.spanToTrace.set(span, options.captureStackTrace)
   }
 
   if (annotationsFromEnv._tag === "Some") {
@@ -2112,6 +2112,9 @@ export const useSpan: {
         if (span.status._tag === "Ended") {
           return
         }
+        if (core.exitIsFailure(exit) && internalCause.spanToTrace.has(span)) {
+          span.attribute("code.stacktrace", internalCause.spanToTrace.get(span)!)
+        }
         span.end(timingEnabled ? clock.unsafeCurrentTimeNanos() : bigint0, exit)
       }))
   })
@@ -2155,15 +2158,22 @@ export const functionWithSpan = <Args extends Array<any>, Ret extends Effect.Eff
   }
 ): (...args: Args) => Unify<Ret> =>
   (function(this: any) {
-    let captureStackTrace: string | boolean = options.captureStackTrace ?? false
+    let captureStackTrace: LazyArg<string | undefined> | boolean = options.captureStackTrace ?? false
     if (options.captureStackTrace !== false) {
       const limit = Error.stackTraceLimit
       Error.stackTraceLimit = 2
       const error = new Error()
       Error.stackTraceLimit = limit
-      if (error.stack !== undefined) {
-        const stack = error.stack.trim().split("\n")
-        captureStackTrace = stack.slice(2).join("\n").trim()
+      let cache: false | string = false
+      captureStackTrace = () => {
+        if (cache !== false) {
+          return cache
+        }
+        if (error.stack) {
+          const stack = error.stack.trim().split("\n")
+          cache = stack.slice(2).join("\n").trim()
+          return cache
+        }
       }
     }
     // eslint-disable-next-line @typescript-eslint/no-this-alias

packages/effect/src/internal/tracer.ts

@@ -118,12 +118,20 @@ export const addSpanStackTrace = (options: Tracer.SpanOptions | undefined): Trac
   Error.stackTraceLimit = 3
   const traceError = new Error()
   Error.stackTraceLimit = limit
-  if (traceError.stack === undefined) {
-    return { ...options, captureStackTrace: false }
-  }
-  const stack = traceError.stack.split("\n")
-  if (!stack[3]) {
-    return { ...options, captureStackTrace: false }
+  let cache: false | string = false
+  return {
+    ...options,
+    captureStackTrace: () => {
+      if (cache !== false) {
+        return cache
+      }
+      if (traceError.stack !== undefined) {
+        const stack = traceError.stack.split("\n")
+        if (stack[3] !== undefined) {
+          cache = stack[3].trim()
+          return cache
+        }
+      }
+    }
   }
-  return { ...options, captureStackTrace: stack[3].trim() }
 }