From 0ebb878166bbe0e354177ae93fe730524956d9a7 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 18 Jun 2025 08:41:47 -0400
Subject: [PATCH] reset should just be a noop after the first call

---
 .../.generated/client-warnings.md             | 26 +++++++++
 .../messages/client-warnings/warnings.md      | 24 +++++++++
 .../internal/client/dom/blocks/boundary.js    |  9 ++++
 .../svelte/src/internal/client/warnings.js    | 11 ++++
 .../error-boundary-reset-premature/_config.js | 54 +++++--------------
 5 files changed, 82 insertions(+), 42 deletions(-)

diff --git a/documentation/docs/98-reference/.generated/client-warnings.md b/documentation/docs/98-reference/.generated/client-warnings.md
index e11d73e819..948f4b9b2f 100644
--- a/documentation/docs/98-reference/.generated/client-warnings.md
+++ b/documentation/docs/98-reference/.generated/client-warnings.md
@@ -300,6 +300,32 @@ Reactive `$state(...)` proxies and the values they proxy have different identiti
 
 To resolve this, ensure you're comparing values where both values were created with `$state(...)`, or neither were. Note that `$state.raw(...)` will _not_ create a state proxy.
 
+### svelte_boundary_reset_noop
+
+```
+A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called
+```
+
+When an error occurs while rendering the contents of a [`<svelte:boundary>`](https://svelte.dev/docs/svelte/svelte-boundary), the `onerror` handler is called with the error plus a `reset` function that attempts to re-render the contents.
+
+This `reset` function should only be called once. After that, it has no effect — in a case like this, where a reference to `reset` is stored outside the boundary, clicking the button while `<Contents />` is rendered will _not_ cause the contents to be rendered again.
+
+```svelte
+<script>
+	let reset;
+</script>
+
+<button onclick={reset}>reset</button>
+
+<svelte:boundary onerror={(e, r) => (reset = r)}>
+	<!-- contents >
+
+	{#snippet failed(e)}
+		<p>oops! {e.message}</p>
+	{/snippet}
+</svelte:boundary>
+```
+
 ### transition_slide_display
 
 ```
diff --git a/packages/svelte/messages/client-warnings/warnings.md b/packages/svelte/messages/client-warnings/warnings.md
index e161fe4bd9..0c75803433 100644
--- a/packages/svelte/messages/client-warnings/warnings.md
+++ b/packages/svelte/messages/client-warnings/warnings.md
@@ -262,6 +262,30 @@ To silence the warning, ensure that `value`:
 
 To resolve this, ensure you're comparing values where both values were created with `$state(...)`, or neither were. Note that `$state.raw(...)` will _not_ create a state proxy.
 
+## svelte_boundary_reset_noop
+
+> A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called
+
+When an error occurs while rendering the contents of a [`<svelte:boundary>`](https://svelte.dev/docs/svelte/svelte-boundary), the `onerror` handler is called with the error plus a `reset` function that attempts to re-render the contents.
+
+This `reset` function should only be called once. After that, it has no effect — in a case like this, where a reference to `reset` is stored outside the boundary, clicking the button while `<Contents />` is rendered will _not_ cause the contents to be rendered again.
+
+```svelte
+<script>
+	let reset;
+</script>
+
+<button onclick={reset}>reset</button>
+
+<svelte:boundary onerror={(e, r) => (reset = r)}>
+	<!-- contents >
+
+	{#snippet failed(e)}
+		<p>oops! {e.message}</p>
+	{/snippet}
+</svelte:boundary>
+```
+
 ## transition_slide_display
 
 > The `slide` transition does not work correctly for elements with `display: %value%`
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 922ab8b3ed..2edc251de9 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -74,7 +74,16 @@ export function boundary(node, props, boundary_fn) {
 				throw error;
 			}
 
+			var did_reset = false;
+
 			var reset = () => {
+				if (did_reset) {
+					w.svelte_boundary_reset_noop();
+					return;
+				}
+
+				did_reset = true;
+
 				pause_effect(boundary_effect);
 
 				with_boundary(boundary, () => {
diff --git a/packages/svelte/src/internal/client/warnings.js b/packages/svelte/src/internal/client/warnings.js
index be09eba492..7c372a0eda 100644
--- a/packages/svelte/src/internal/client/warnings.js
+++ b/packages/svelte/src/internal/client/warnings.js
@@ -43,6 +43,17 @@ export function console_log_state(method) {
 	}
 }
 
+/**
+ * A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called
+ */
+export function svelte_boundary_reset_noop() {
+	if (DEV) {
+		console.warn(`%c[svelte] svelte_boundary_reset_noop\n%cA \`<svelte:boundary>\` \`reset\` function only resets the boundary the first time it is called\nhttps://svelte.dev/e/svelte_boundary_reset_noop`, bold, normal);
+	} else {
+		console.warn(`https://svelte.dev/e/svelte_boundary_reset_noop`);
+	}
+}
+
 /**
  * %handler% should be a function. Did you mean to %suggestion%?
  * @param {string} handler
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js
index 048413ad7b..687961e721 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js
@@ -7,52 +7,22 @@ export default test({
 		<button>toggle</button>
 	`,
 
-	expect_unhandled_rejections: true,
+	async test({ assert, target, warnings }) {
+		const [btn] = target.querySelectorAll('button');
 
-	async test({ assert, target, warnings, window }) {
-		// @ts-expect-error
-		const __expected_error = (window.__expected_error = { v: false });
-
-		window.addEventListener('error', (e) => {
-			// @ts-expect-error when in hydrate mode we can't access variables in the scope
-			const __expected_error = window.__expected_error;
-
-			if (__expected_error.v) {
-				assert.include(e.error.message, 'error on template render');
-			} else {
-				assert.fail('Error was not expected: ' + e.error.message);
-			}
-			e.preventDefault();
-		});
-
-		const btn = target.querySelector('button');
-
-		// 1st click — error caught, fallback visible
-		btn?.click();
-		flushSync();
+		flushSync(() => btn.click());
 		assert.htmlEqual(target.innerHTML, `<div>err</div><button>toggle</button>`);
+		assert.deepEqual(warnings, []);
 
-		// 2nd click — reset succeeds, normal render
-		btn?.click();
-		flushSync();
-		assert.htmlEqual(
-			target.innerHTML,
-			`
-				normal content
-				<button>toggle</button>
-			`
-		);
-
-		// 3rd click — mount-time crash escapes, boundary empty
-		__expected_error.v = true;
-		btn?.click();
-		flushSync();
-		__expected_error.v = false;
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, `normal content <button>toggle</button>`);
+		assert.deepEqual(warnings, []);
 
-		// Check that the warning is being showed to the user
-		assert.include(warnings[0], 'reset() was invoked');
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, `<div>err</div><button>toggle</button>`);
 
-		// boundary content empty; only button remains
-		assert.htmlEqual(target.innerHTML, `<button>toggle</button>`);
+		assert.deepEqual(warnings, [
+			'A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called'
+		]);
 	}
 });