fix(sveltekit): support SvelteKit 3 handleError input

.changeset/sveltekit-3-handle-error.md

@@ -0,0 +1,5 @@
+---
+"evlog": patch
+---
+
+`createEvlogHooks().handleError` and `evlogHandleError()` now accept SvelteKit 3's `handleError` input (`kind`, `error`, `event`) and type-check as Kit 3's `HandleServerError`. On SvelteKit 3, errors that are not an `EvlogError` keep Kit's own status and message instead of being overwritten with `undefined`, which made production responses return HTTP 200. The hook no longer reads Kit 3's deprecated `status` and `message` input properties, so dev mode stops logging deprecation warnings. SvelteKit 2 behavior is unchanged.

packages/evlog/src/sveltekit/index.ts

@@ -48,13 +48,12 @@ const integration = defineFrameworkIntegration<SvelteKitRequestEvent>({
 
 /**
  * SvelteKit `HandleServerError` signature — avoids a hard dependency on `@sveltejs/kit`.
+ * Kit 2 passes `status` and `message`; Kit 3 passes a `kind` discriminant instead.
  */
 type SvelteKitHandleServerError = (input: {
   error: unknown
   event: { request: Request; url: URL; locals: Record<string, any> }
-  status: number
-  message: string
-}) => MaybePromise<void | AppError>
+} & ({ kind: string } | { status: number; message: string })) => MaybePromise<void | AppError>
 
 type MaybePromise<T> = T | Promise<T>
 
@@ -203,8 +202,8 @@ export function evlog(options: EvlogSvelteKitOptions = {}): SvelteKitHandle {
  * Create an evlog error handler for SvelteKit.
  *
  * Logs unhandled errors via `event.locals.log` (if available) and returns
- * structured error responses for `EvlogError` instances. For non-evlog errors,
- * returns a generic error response with sanitized messages in production.
+ * structured error responses for `EvlogError` instances. Other errors keep
+ * SvelteKit's own status and message. Supports SvelteKit 2 and 3.
  *
  * @example
  * ```ts
@@ -216,7 +215,8 @@ export function evlog(options: EvlogSvelteKitOptions = {}): SvelteKitHandle {
  * ```
  */
 export function evlogHandleError(): SvelteKitHandleServerError {
-  return ({ error, event, status, message }) => {
+  return (input) => {
+    const { error, event } = input
     const logger = isRequestLogger(event.locals.log) ? event.locals.log : undefined
 
     if (logger && error instanceof Error) {
@@ -229,13 +229,15 @@ export function evlogHandleError(): SvelteKitHandleServerError {
       const errorStatus = extractErrorStatus(evlogError)
       const response = serializeEvlogErrorResponse(evlogError, event.url.pathname)
       return {
-        message: typeof response.message === 'string' ? response.message : message,
+        message: evlogError.message,
         status: errorStatus,
         ...readEvlogResponseData(response),
       }
     }
 
-    return { message, status }
+    // Kit 3 fills in status and message itself; its input getters for them are deprecated
+    if ('kind' in input) return
+    return { message: input.message, status: input.status }
   }
 }
 

packages/evlog/test/frameworks/sveltekit.test.ts

@@ -543,6 +543,61 @@ describe('evlog/sveltekit', () => {
 
       expect(result.message).toBe('Internal Error')
     })
+
+    describe('SvelteKit 3 input (#911)', () => {
+      function createKit3Input(kind: 'unknown' | 'framework', error: unknown, event: ReturnType<typeof createMockEvent>) {
+        const deprecatedReads: string[] = []
+        const input = { kind, error, event }
+        // Kit 3 dev mode exposes `status` and `message` as deprecated getters that warn on access
+        Object.defineProperties(input, {
+          status: {
+            get() {
+              deprecatedReads.push('status')
+              return 500
+            },
+          },
+          message: {
+            get() {
+              deprecatedReads.push('message')
+              return 'Internal Error'
+            },
+          },
+        })
+        return { input, deprecatedReads }
+      }
+
+      it('logs an unknown error and returns nothing so Kit keeps its defaults', () => {
+        const handleError = evlogHandleError()
+        const event = createMockEvent('GET', '/api/fail')
+        const logError = vi.fn()
+        event.locals.log = { error: logError, emit: () => null }
+        const error = new Error('Something broke')
+        const { input, deprecatedReads } = createKit3Input('unknown', error, event)
+
+        expect(handleError(input)).toBeUndefined()
+        expect(logError).toHaveBeenCalledWith(error)
+        expect(deprecatedReads).toEqual([])
+      })
+
+      it('returns the EvlogError status and message', () => {
+        const handleError = evlogHandleError()
+        const event = createMockEvent('GET', '/api/checkout')
+        const error = new EvlogError({ message: 'Payment failed', status: 402, why: 'Card declined' })
+        const { input, deprecatedReads } = createKit3Input('unknown', error, event)
+
+        expect(handleError(input)).toEqual({ message: 'Payment failed', status: 402, why: 'Card declined' })
+        expect(deprecatedReads).toEqual([])
+      })
+
+      it('returns nothing for a framework error', () => {
+        const handleError = evlogHandleError()
+        const event = createMockEvent('GET', '/missing')
+        const { input, deprecatedReads } = createKit3Input('framework', { status: 404, message: 'Not Found' }, event)
+
+        expect(handleError(input)).toBeUndefined()
+        expect(deprecatedReads).toEqual([])
+      })
+    })
   })
 
   describe('createEvlogHooks()', () => {