fix: ensure `<svelte:boundary>` properly removes error content in production mode (#15793)

* fix: ensure <svelte:boundary> properly removes error content in production mode

* add changeset

.changeset/eleven-roses-speak.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure <svelte:boundary> properly removes error content in production mode

packages/svelte/src/internal/client/runtime.js

@@ -291,16 +291,7 @@ export function handle_error(error, effect, previous_effect, component_context)
 		is_throwing_error = true;
 	}
 
-	if (
+	if (DEV && component_context !== null && error instanceof Error && !handled_errors.has(error)) {
-		!DEV ||
-		component_context === null ||
-		!(error instanceof Error) ||
-		handled_errors.has(error)
-	) {
-		propagate_error(error, effect);
-		return;
-	}
-
 		handled_errors.add(error);
 
 		const component_stack = [];
@@ -315,7 +306,6 @@ export function handle_error(error, effect, previous_effect, component_context)
 		let current_context = component_context;
 
 		while (current_context !== null) {
-		if (DEV) {
 			/** @type {string} */
 			var filename = current_context.function?.[FILENAME];
 
@@ -323,14 +313,14 @@ export function handle_error(error, effect, previous_effect, component_context)
 				const file = filename.split('/').pop();
 				component_stack.push(file);
 			}
-		}
 
 			current_context = current_context.p;
 		}
 
 		const indent = is_firefox ? '  ' : '\t';
 		define_property(error, 'message', {
-		value: error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
+			value:
+				error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
 		});
 		define_property(error, 'component_stack', {
 			value: component_stack
@@ -353,6 +343,7 @@ export function handle_error(error, effect, previous_effect, component_context)
 				value: new_lines.join('\n')
 			});
 		}
+	}
 
 	propagate_error(error, effect);
 

packages/svelte/tests/runtime-runes/samples/error-boundary-22/Child.svelte

@@ -0,0 +1,3 @@
+<script>
+	throw new Error();
+</script>

packages/svelte/tests/runtime-runes/samples/error-boundary-22/_config.js

@@ -0,0 +1,11 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	test({ assert, target }) {
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, '<p>error occurred</p>');
+	}
+});

packages/svelte/tests/runtime-runes/samples/error-boundary-22/main.svelte

@@ -0,0 +1,15 @@
+<script>
+	import Child from "./Child.svelte"
+</script>
+
+<svelte:boundary>
+	<p>This should be removed</p>
+
+	{#if true}
+		<Child />
+	{/if}
+
+	{#snippet failed()}
+		<p>error occurred</p>
+	{/snippet}
+</svelte:boundary>