From 6c2064b195f7dfa4c8ec61f0b7533cfd2f7f7ab3 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 7 Jul 2025 23:20:19 -0400
Subject: [PATCH] only apply error adjustments when error escapes boundaries

---
 .../src/internal/client/error-handling.js     | 45 ++++++++++++++-----
 1 file changed, 33 insertions(+), 12 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index c9a888658c..8e93923c46 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -7,6 +7,8 @@ import { ERROR_VALUE, BOUNDARY_EFFECT, EFFECT_RAN } from './constants.js';
 import { define_property, get_descriptor } from '../shared/utils.js';
 import { active_effect, active_reaction } from './runtime.js';
 
+const adjustments = new WeakMap();
+
 /**
  * @param {unknown} error
  */
@@ -19,14 +21,18 @@ export function handle_error(error) {
 		return error;
 	}
 
-	if (DEV && error instanceof Error) {
-		// adjust_error(error, effect);
+	if (DEV && error instanceof Error && !adjustments.has(error)) {
+		adjustments.set(error, get_adjustments(error, effect));
 	}
 
 	if ((effect.f & EFFECT_RAN) === 0) {
 		// if the error occurred while creating this subtree, we let it
 		// bubble up until it hits a boundary that can handle it
 		if ((effect.f & BOUNDARY_EFFECT) === 0) {
+			if (!effect.parent && error instanceof Error) {
+				apply_adjustments(error);
+			}
+
 			throw error;
 		}
 
@@ -53,6 +59,10 @@ export function invoke_error_boundary(error, effect) {
 		effect = effect.parent;
 	}
 
+	if (error instanceof Error) {
+		apply_adjustments(error);
+	}
+
 	throw error;
 }
 
@@ -64,7 +74,7 @@ const adjusted_errors = new WeakSet();
  * @param {Error} error
  * @param {Effect} effect
  */
-function adjust_error(error, effect) {
+function get_adjustments(error, effect) {
 	if (adjusted_errors.has(error)) return;
 	adjusted_errors.add(error);
 
@@ -83,17 +93,28 @@ function adjust_error(error, effect) {
 		context = context.p;
 	}
 
-	define_property(error, 'message', {
-		value: error.message + `\n${component_stack}\n`
-	});
+	return {
+		message: error.message + `\n${component_stack}\n`,
+		stack: error.stack
+			?.split('\n')
+			.filter((line) => !line.includes('svelte/src/internal'))
+			.join('\n')
+	};
+}
+
+/**
+ * @param {Error} error
+ */
+function apply_adjustments(error) {
+	const adjusted = adjustments.get(error);
+
+	if (adjusted) {
+		define_property(error, 'message', {
+			value: adjusted.message
+		});
 
-	if (error.stack) {
-		// Filter out internal modules
 		define_property(error, 'stack', {
-			value: error.stack
-				.split('\n')
-				.filter((line) => !line.includes('svelte/src/internal'))
-				.join('\n')
+			value: adjusted.stack
 		});
 	}
 }