🔧 fix: keep mapResponse hooks in the toResponse fast path

Author: MarcelOlsen

src/compose.ts

@@ -2529,11 +2529,8 @@ export const composeErrorHandler = (app: AnyElysia) => {
 		adapterVariables +
 		`}=inject\n`
 
-	fnLiteral += `return ${
-		app.event.error?.find(isAsync) || app.event.mapResponse?.find(isAsync)
-			? 'async '
-			: ''
-	}function(context,error,skipGlobal){`
+	// Always make error handler async since toResponse() may return promises
+	fnLiteral += `return async function(context,error,skipGlobal){`
 
 	fnLiteral += ''
 
@@ -2598,19 +2595,12 @@ export const composeErrorHandler = (app: AnyElysia) => {
 	const saveResponse =
 		hasTrace || !!hooks.afterResponse?.length ? 'context.response = ' : ''
 
-	// Check for toResponse() first to handle errors with custom response methods
-	// This takes precedence over onError hooks, as the error defines its own response
-	// BUT exclude ValidationError and TransformDecodeError to allow proper validation error handling
 	fnLiteral +=
 		`if(typeof error?.toResponse==='function'&&error.constructor.name!=="ValidationError"&&error.constructor.name!=="TransformDecodeError"){` +
-		`const raw=error.toResponse()\n` +
-		`const apply=(resolved)=>{` +
-		`if(resolved instanceof Response)set.status=resolved.status\n` +
-		afterResponse() +
-		`return context.response=context.responseValue=mapResponse(${saveResponse}resolved,set${adapter.mapResponseContext})\n` +
-		`}\n` +
-		`if(typeof raw?.then==='function')return raw.then(apply)\n` +
-		`return apply(raw)\n` +
+		`let raw=error.toResponse()\n` +
+		`if(typeof raw?.then==='function')raw=await raw\n` +
+		`if(raw instanceof Response)set.status=raw.status\n` +
+		`context.response=context.responseValue=raw\n` +
 		`}\n`
 
 	if (app.event.error)
@@ -2621,7 +2611,7 @@ export const composeErrorHandler = (app: AnyElysia) => {
 				isAsync(handler) ? 'await ' : ''
 			}onError[${i}](context)\n`
 
-			fnLiteral += 'if(skipGlobal!==true){'
+			fnLiteral += 'if(skipGlobal!==true&&!context.response){'
 
 			if (hasReturn(handler)) {
 				fnLiteral +=
@@ -2675,7 +2665,7 @@ export const composeErrorHandler = (app: AnyElysia) => {
 		`\n}\n`
 
 	fnLiteral +=
-		`if(error instanceof Error){` +
+		`if(!context.response&&error instanceof Error){` +
 		afterResponse() +
 		adapter.unknownError +
 		`\n}`

src/dynamic-handle.ts

@@ -684,7 +684,18 @@ export const createDynamicErrorHandler = (app: AnyElysia) => {
 		const errorContext = Object.assign(context, { error, code: error.code })
 		errorContext.set = context.set
 
-		if (app.event.error)
+		// @ts-expect-error
+		if (typeof error?.toResponse === 'function' &&
+			error.constructor.name !== 'ValidationError' &&
+			error.constructor.name !== 'TransformDecodeError') {
+			// @ts-expect-error
+			let raw = error.toResponse()
+			if (typeof raw?.then === 'function') raw = await raw
+			if (raw instanceof Response) context.set.status = raw.status
+			context.response = raw
+		}
+
+		if (!context.response && app.event.error)
 			for (let i = 0; i < app.event.error.length; i++) {
 				const hook = app.event.error[i]
 				let response = hook.fn(errorContext as any)
@@ -696,6 +707,19 @@ export const createDynamicErrorHandler = (app: AnyElysia) => {
 					))
 			}
 
+		if (context.response) {
+			if (app.event.mapResponse)
+				for (let i = 0; i < app.event.mapResponse.length; i++) {
+					const hook = app.event.mapResponse[i]
+					let response = hook.fn(errorContext as any)
+					if (response instanceof Promise) response = await response
+					if (response !== undefined && response !== null)
+						context.response = response
+				}
+
+			return mapResponse(context.response, context.set)
+		}
+
 		return new Response(
 			typeof error.cause === 'string' ? error.cause : error.message,
 			{