ensure multiline error messages are preserved in cause rendering (#2981)

.changeset/long-tools-sleep.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+ensure multiline error messages are preserved in cause rendering

packages/effect/src/internal/cause.ts

@@ -1055,7 +1055,7 @@ export const spanToTrace = globalValue("effect/Tracer/spanToTrace", () => new We
 
 const prettyErrorStack = (message: string, stack: string, span?: Span | undefined): string => {
   const out: Array<string> = [message]
-  const lines = stack.split("\n")
+  const lines = stack.startsWith(message) ? stack.slice(message.length).split("\n") : stack.split("\n")
 
   for (let i = 1; i < lines.length; i++) {
     if (lines[i].includes("Generator.next")) {

packages/effect/test/Effect/cause-rendering.test.ts

@@ -141,4 +141,17 @@ describe("Effect", () => {
       yield* Effect.void
       it.expect({ foo: "ok" }).toStrictEqual({ foo: "bar" })
     }))
+
+  it.effect("multiline message", () =>
+    Effect.gen(function*() {
+      const cause = yield* Effect.fail(new Error("Multi-line\nerror\nmessage")).pipe(
+        Effect.sandbox,
+        Effect.flip
+      )
+      const pretty = Cause.pretty(cause)
+      assert.isTrue(pretty.startsWith(`Error: Multi-line
+error
+message
+    at`))
+    }))
 })