From 67a6753f0b83427e00e26cf2e6d5cfaeabd69cd7 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sat, 15 Mar 2025 13:32:46 -0700
Subject: [PATCH 01/10] init

---
 .changeset/bright-jeans-compare.md              |  5 +++++
 .../98-reference/.generated/shared-errors.md    |  6 ++++++
 .../svelte/messages/shared-errors/errors.md     |  4 ++++
 .../3-transform/client/visitors/SnippetBlock.js | 17 ++++++++++++++---
 .../3-transform/server/visitors/SnippetBlock.js |  5 ++++-
 .../src/internal/client/dev/validation.js       | 15 +++++++++++++++
 packages/svelte/src/internal/client/index.js    |  1 +
 packages/svelte/src/internal/server/dev.js      | 10 ++++++++++
 packages/svelte/src/internal/server/index.js    |  2 +-
 packages/svelte/src/internal/shared/errors.js   | 15 +++++++++++++++
 10 files changed, 75 insertions(+), 5 deletions(-)
 create mode 100644 .changeset/bright-jeans-compare.md
 create mode 100644 packages/svelte/src/internal/client/dev/validation.js

diff --git a/.changeset/bright-jeans-compare.md b/.changeset/bright-jeans-compare.md
new file mode 100644
index 000000000000..206fecdecfbf
--- /dev/null
+++ b/.changeset/bright-jeans-compare.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+fix: add snippet argument validation in dev
diff --git a/documentation/docs/98-reference/.generated/shared-errors.md b/documentation/docs/98-reference/.generated/shared-errors.md
index 0102aafcbca1..09652c7d0cb7 100644
--- a/documentation/docs/98-reference/.generated/shared-errors.md
+++ b/documentation/docs/98-reference/.generated/shared-errors.md
@@ -30,6 +30,12 @@ This error would be thrown in a setup like this:
 
 Here, `List.svelte` is using `{@render children(item)` which means it expects `Parent.svelte` to use snippets. Instead, `Parent.svelte` uses the deprecated `let:` directive. This combination of APIs is incompatible, hence the error.
 
+### invalid_snippet_arguments
+
+```
+A snippet function was passed invalid arguments. A snippet function should only be called via `{@render ...}`
+```
+
 ### lifecycle_outside_component
 
 ```
diff --git a/packages/svelte/messages/shared-errors/errors.md b/packages/svelte/messages/shared-errors/errors.md
index 8b4c61303a07..6367ce726e4e 100644
--- a/packages/svelte/messages/shared-errors/errors.md
+++ b/packages/svelte/messages/shared-errors/errors.md
@@ -26,6 +26,10 @@ This error would be thrown in a setup like this:
 
 Here, `List.svelte` is using `{@render children(item)` which means it expects `Parent.svelte` to use snippets. Instead, `Parent.svelte` uses the deprecated `let:` directive. This combination of APIs is incompatible, hence the error.
 
+## invalid_snippet_arguments
+
+> A snippet function was passed invalid arguments. A snippet function should only be called via `{@render ...}`
+
 ## lifecycle_outside_component
 
 > `%name%(...)` can only be used during component initialisation
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SnippetBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SnippetBlock.js
index 7a0d6981b52a..7eb043aa5d11 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SnippetBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SnippetBlock.js
@@ -1,4 +1,4 @@
-/** @import { BlockStatement, Expression, Identifier, Pattern, Statement } from 'estree' */
+/** @import { AssignmentPattern, BlockStatement, Expression, Identifier, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import { dev } from '../../../../state.js';
@@ -12,7 +12,7 @@ import { get_value } from './shared/declarations.js';
  */
 export function SnippetBlock(node, context) {
 	// TODO hoist where possible
-	/** @type {Pattern[]} */
+	/** @type {(Identifier | AssignmentPattern)[]} */
 	const args = [b.id('$$anchor')];
 
 	/** @type {BlockStatement} */
@@ -66,7 +66,18 @@ export function SnippetBlock(node, context) {
 			}
 		}
 	}
-
+	if (dev) {
+		declarations.unshift(
+			b.stmt(
+				b.call(
+					'$.validate_snippet_args',
+					.../** @type {Identifier[]} */ (
+						args.map((arg) => (arg?.type === 'Identifier' ? arg : arg?.left))
+					)
+				)
+			)
+		);
+	}
 	body = b.block([
 		...declarations,
 		.../** @type {BlockStatement} */ (context.visit(node.body, child_state)).body
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/SnippetBlock.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/SnippetBlock.js
index eb839179271a..cae3e7d79c94 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/SnippetBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/SnippetBlock.js
@@ -1,6 +1,7 @@
 /** @import { BlockStatement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types.js' */
+import { dev } from '../../../../state.js';
 import * as b from '../../../../utils/builders.js';
 
 /**
@@ -13,7 +14,9 @@ export function SnippetBlock(node, context) {
 		[b.id('$$payload'), ...node.parameters],
 		/** @type {BlockStatement} */ (context.visit(node.body))
 	);
-
+	if (dev) {
+		fn.body.body.unshift(b.stmt(b.call('$.validate_snippet_args', b.id('$$payload'))));
+	}
 	// @ts-expect-error - TODO remove this hack once $$render_inner for legacy bindings is gone
 	fn.___snippet = true;
 
diff --git a/packages/svelte/src/internal/client/dev/validation.js b/packages/svelte/src/internal/client/dev/validation.js
new file mode 100644
index 000000000000..bfb81d81da2e
--- /dev/null
+++ b/packages/svelte/src/internal/client/dev/validation.js
@@ -0,0 +1,15 @@
+import { invalid_snippet_arguments } from '../../shared/errors';
+/**
+ * @param {Node} anchor
+ * @param {...(()=>any)[]} args
+ */
+export function validate_snippet_args(anchor, ...args) {
+	if (typeof anchor !== 'object' || !(anchor instanceof Node)) {
+		invalid_snippet_arguments();
+	}
+	for (let arg of args) {
+		if (typeof arg !== 'function') {
+			invalid_snippet_arguments();
+		}
+	}
+}
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 31da00dbb448..e833934634e1 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -16,6 +16,7 @@ export {
 export { check_target, legacy_api } from './dev/legacy.js';
 export { trace } from './dev/tracing.js';
 export { inspect } from './dev/inspect.js';
+export { validate_snippet_args } from './dev/validation.js';
 export { await_block as await } from './dom/blocks/await.js';
 export { if_block as if } from './dom/blocks/if.js';
 export { key_block as key } from './dom/blocks/key.js';
diff --git a/packages/svelte/src/internal/server/dev.js b/packages/svelte/src/internal/server/dev.js
index ecf4e67429ac..2a51d4a7c5c6 100644
--- a/packages/svelte/src/internal/server/dev.js
+++ b/packages/svelte/src/internal/server/dev.js
@@ -5,6 +5,7 @@ import {
 	is_tag_valid_with_parent
 } from '../../html-tree-validation.js';
 import { current_component } from './context.js';
+import { invalid_snippet_arguments } from '../shared/errors';
 
 /**
  * @typedef {{
@@ -98,3 +99,12 @@ export function push_element(payload, tag, line, column) {
 export function pop_element() {
 	parent = /** @type {Element} */ (parent).parent;
 }
+
+/**
+ * @param {Payload} payload
+ */
+export function validate_snippet_args(payload) {
+	if (typeof payload !== 'object' || !('out' in payload)) {
+		invalid_snippet_arguments();
+	}
+}
diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index 6098b496c5ac..a5c78f8eb600 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -541,7 +541,7 @@ export { html } from './blocks/html.js';
 
 export { push, pop } from './context.js';
 
-export { push_element, pop_element } from './dev.js';
+export { push_element, pop_element, validate_snippet_args } from './dev.js';
 
 export { snapshot } from '../shared/clone.js';
 
diff --git a/packages/svelte/src/internal/shared/errors.js b/packages/svelte/src/internal/shared/errors.js
index 26d6822cdb29..7d31d6e91049 100644
--- a/packages/svelte/src/internal/shared/errors.js
+++ b/packages/svelte/src/internal/shared/errors.js
@@ -17,6 +17,21 @@ export function invalid_default_snippet() {
 	}
 }
 
+/**
+ * A snippet function was passed invalid arguments. A snippet function should only be called via `{@render ...}`
+ * @returns {never}
+ */
+export function invalid_snippet_arguments() {
+	if (DEV) {
+		const error = new Error(`invalid_snippet_arguments\nA snippet function was passed invalid arguments. A snippet function should only be called via \`{@render ...}\`\nhttps://svelte.dev/e/invalid_snippet_arguments`);
+
+		error.name = 'Svelte error';
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/invalid_snippet_arguments`);
+	}
+}
+
 /**
  * `%name%(...)` can only be used during component initialisation
  * @param {string} name

From 926331f5d706fcd452759df314db33090e54ff96 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sat, 15 Mar 2025 13:36:29 -0700
Subject: [PATCH 02/10] fix

---
 packages/svelte/src/internal/client/dev/validation.js | 2 +-
 packages/svelte/src/internal/server/dev.js            | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/internal/client/dev/validation.js b/packages/svelte/src/internal/client/dev/validation.js
index bfb81d81da2e..e41e4c46283d 100644
--- a/packages/svelte/src/internal/client/dev/validation.js
+++ b/packages/svelte/src/internal/client/dev/validation.js
@@ -1,4 +1,4 @@
-import { invalid_snippet_arguments } from '../../shared/errors';
+import { invalid_snippet_arguments } from '../../shared/errors.js';
 /**
  * @param {Node} anchor
  * @param {...(()=>any)[]} args
diff --git a/packages/svelte/src/internal/server/dev.js b/packages/svelte/src/internal/server/dev.js
index 2a51d4a7c5c6..73c5beb62057 100644
--- a/packages/svelte/src/internal/server/dev.js
+++ b/packages/svelte/src/internal/server/dev.js
@@ -5,7 +5,7 @@ import {
 	is_tag_valid_with_parent
 } from '../../html-tree-validation.js';
 import { current_component } from './context.js';
-import { invalid_snippet_arguments } from '../shared/errors';
+import { invalid_snippet_arguments } from '../shared/errors.js';
 
 /**
  * @typedef {{

From 6f64812ea14ee40c94c326353fbd0165f38f8c10 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Mon, 17 Mar 2025 17:39:58 -0700
Subject: [PATCH 03/10] make `Payload` a class

---
 .../src/internal/server/blocks/snippet.js     |  2 +-
 packages/svelte/src/internal/server/dev.js    |  5 +--
 packages/svelte/src/internal/server/index.js  | 31 +++++++++++++------
 .../svelte/src/internal/server/types.d.ts     | 13 --------
 4 files changed, 25 insertions(+), 26 deletions(-)

diff --git a/packages/svelte/src/internal/server/blocks/snippet.js b/packages/svelte/src/internal/server/blocks/snippet.js
index 3c5e8607905b..466de1926adc 100644
--- a/packages/svelte/src/internal/server/blocks/snippet.js
+++ b/packages/svelte/src/internal/server/blocks/snippet.js
@@ -1,5 +1,5 @@
 /** @import { Snippet } from 'svelte' */
-/** @import { Payload } from '#server' */
+/** @import { Payload } from '../index' */
 /** @import { Getters } from '#shared' */
 
 /**
diff --git a/packages/svelte/src/internal/server/dev.js b/packages/svelte/src/internal/server/dev.js
index 73c5beb62057..2df8e1133310 100644
--- a/packages/svelte/src/internal/server/dev.js
+++ b/packages/svelte/src/internal/server/dev.js
@@ -1,4 +1,4 @@
-/** @import { Component, Payload } from '#server' */
+/** @import { Component } from '#server' */
 import { FILENAME } from '../../constants.js';
 import {
 	is_tag_valid_with_ancestor,
@@ -6,6 +6,7 @@ import {
 } from '../../html-tree-validation.js';
 import { current_component } from './context.js';
 import { invalid_snippet_arguments } from '../shared/errors.js';
+import { Payload } from './index.js';
 
 /**
  * @typedef {{
@@ -104,7 +105,7 @@ export function pop_element() {
  * @param {Payload} payload
  */
 export function validate_snippet_args(payload) {
-	if (typeof payload !== 'object' || !('out' in payload)) {
+	if (typeof payload !== 'object' || !(payload instanceof Payload)) {
 		invalid_snippet_arguments();
 	}
 }
diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index a5c78f8eb600..c6248c619d14 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -1,5 +1,5 @@
 /** @import { ComponentType, SvelteComponent } from 'svelte' */
-/** @import { Component, Payload, RenderOutput } from '#server' */
+/** @import { Component, RenderOutput } from '#server' */
 /** @import { Store } from '#shared' */
 export { FILENAME, HMR } from '../../constants.js';
 import { attr, clsx, to_class, to_style } from '../shared/attributes.js';
@@ -96,6 +96,24 @@ function props_id_generator(prefix) {
 	return () => `${prefix}s${uid++}`;
 }
 
+class Payload {
+	out = '';
+	/**@type {Set<{ hash: string; code: string }>} */
+	css = new Set();
+	uid = () => '';
+	head = {
+		/**@type {Set<{ hash: string; code: string }>} */
+		css: new Set(),
+		title: '',
+		out: '',
+		uid: () => ''
+	};
+	constructor(idPrefix = '') {
+		this.uid = props_id_generator(idPrefix);
+		this.head.uid = this.uid;
+	}
+}
+
 /**
  * Only available on the server and when compiling with the `server` option.
  * Takes a component and returns an object with `body` and `head` properties on it, which you can use to populate the HTML when server-rendering your app.
@@ -105,14 +123,7 @@ function props_id_generator(prefix) {
  * @returns {RenderOutput}
  */
 export function render(component, options = {}) {
-	const uid = props_id_generator(options.idPrefix ? options.idPrefix + '-' : '');
-	/** @type {Payload} */
-	const payload = {
-		out: '',
-		css: new Set(),
-		head: { title: '', out: '', css: new Set(), uid },
-		uid
-	};
+	const payload = new Payload(options.idPrefix ? options.idPrefix + '' : '');
 
 	const prev_on_destroy = on_destroy;
 	on_destroy = [];
@@ -535,7 +546,7 @@ export function props_id(payload) {
 	return uid;
 }
 
-export { attr, clsx };
+export { attr, clsx, Payload };
 
 export { html } from './blocks/html.js';
 
diff --git a/packages/svelte/src/internal/server/types.d.ts b/packages/svelte/src/internal/server/types.d.ts
index 2fffdbbdf0bb..6b0fc146c419 100644
--- a/packages/svelte/src/internal/server/types.d.ts
+++ b/packages/svelte/src/internal/server/types.d.ts
@@ -11,19 +11,6 @@ export interface Component {
 	function?: any;
 }
 
-export interface Payload {
-	out: string;
-	css: Set<{ hash: string; code: string }>;
-	head: {
-		title: string;
-		out: string;
-		uid: () => string;
-		css: Set<{ hash: string; code: string }>;
-	};
-	/** Function that generates a unique ID */
-	uid: () => string;
-}
-
 export interface RenderOutput {
 	/** HTML that goes into the `<head>` */
 	head: string;

From af766dfa40c179d67cc567794dcf5f1e74732f6e Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Mon, 17 Mar 2025 17:42:24 -0700
Subject: [PATCH 04/10] doh

---
 packages/svelte/src/internal/server/index.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index c6248c619d14..633fc4805b2b 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -123,7 +123,7 @@ class Payload {
  * @returns {RenderOutput}
  */
 export function render(component, options = {}) {
-	const payload = new Payload(options.idPrefix ? options.idPrefix + '' : '');
+	const payload = new Payload(options.idPrefix ? options.idPrefix + '-' : '');
 
 	const prev_on_destroy = on_destroy;
 	on_destroy = [];

From 805fe77a3dfdc217f0b8a723d932e8428ddccb6e Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Mon, 17 Mar 2025 17:45:57 -0700
Subject: [PATCH 05/10] lint

---
 packages/svelte/src/internal/server/index.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index 633fc4805b2b..00a7977c3456 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -108,8 +108,8 @@ class Payload {
 		out: '',
 		uid: () => ''
 	};
-	constructor(idPrefix = '') {
-		this.uid = props_id_generator(idPrefix);
+	constructor(id_prefix = '') {
+		this.uid = props_id_generator(id_prefix);
 		this.head.uid = this.uid;
 	}
 }

From 31b4bb6bb30d347408f6fcf19b2c0ed117c4ddf1 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Tue, 1 Apr 2025 08:14:42 -0700
Subject: [PATCH 06/10] tweak changeset

---
 .changeset/bright-jeans-compare.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.changeset/bright-jeans-compare.md b/.changeset/bright-jeans-compare.md
index 206fecdecfbf..eaec658e0343 100644
--- a/.changeset/bright-jeans-compare.md
+++ b/.changeset/bright-jeans-compare.md
@@ -1,5 +1,5 @@
 ---
-'svelte': minor
+'svelte': patch
 ---
 
 fix: add snippet argument validation in dev

From eaca5268ab40412a2bfc894c97fc7c53f2a8780f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Apr 2025 18:59:23 -0400
Subject: [PATCH 07/10] fix

---
 packages/svelte/src/internal/server/index.js | 62 +++++++++++---------
 1 file changed, 34 insertions(+), 28 deletions(-)

diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index a5d8019a107c..4400aca41882 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -23,22 +23,46 @@ import { reset_elements } from './dev.js';
 const INVALID_ATTR_NAME_CHAR_REGEX =
 	/[\s'">/=\u{FDD0}-\u{FDEF}\u{FFFE}\u{FFFF}\u{1FFFE}\u{1FFFF}\u{2FFFE}\u{2FFFF}\u{3FFFE}\u{3FFFF}\u{4FFFE}\u{4FFFF}\u{5FFFE}\u{5FFFF}\u{6FFFE}\u{6FFFF}\u{7FFFE}\u{7FFFF}\u{8FFFE}\u{8FFFF}\u{9FFFE}\u{9FFFF}\u{AFFFE}\u{AFFFF}\u{BFFFE}\u{BFFFF}\u{CFFFE}\u{CFFFF}\u{DFFFE}\u{DFFFF}\u{EFFFE}\u{EFFFF}\u{FFFFE}\u{FFFFF}\u{10FFFE}\u{10FFFF}]/u;
 
+class Payload {
+	/** @type {Set<{ hash: string; code: string }>} */
+	css = new Set();
+	out = '';
+	uid = () => '';
+
+	head = {
+		/** @type {Set<{ hash: string; code: string }>} */
+		css: new Set(),
+		title: '',
+		out: '',
+		uid: () => ''
+	};
+
+	constructor(id_prefix = '') {
+		this.uid = props_id_generator(id_prefix);
+		this.head.uid = this.uid;
+	}
+}
+
 /**
+ * Used in legacy mode to handle bindings
  * @param {Payload} to_copy
  * @returns {Payload}
  */
 export function copy_payload({ out, css, head, uid }) {
-	return {
-		out,
-		css: new Set(css),
-		head: {
-			title: head.title,
-			out: head.out,
-			css: new Set(head.css),
-			uid: head.uid
-		},
-		uid
+	const payload = new Payload();
+
+	payload.out = out;
+	payload.css = new Set(css);
+	payload.uid = uid;
+
+	payload.head = {
+		title: head.title,
+		out: head.out,
+		css: new Set(head.css),
+		uid: head.uid
 	};
+
+	return payload;
 }
 
 /**
@@ -97,24 +121,6 @@ function props_id_generator(prefix) {
 	return () => `${prefix}s${uid++}`;
 }
 
-class Payload {
-	out = '';
-	/**@type {Set<{ hash: string; code: string }>} */
-	css = new Set();
-	uid = () => '';
-	head = {
-		/**@type {Set<{ hash: string; code: string }>} */
-		css: new Set(),
-		title: '',
-		out: '',
-		uid: () => ''
-	};
-	constructor(id_prefix = '') {
-		this.uid = props_id_generator(id_prefix);
-		this.head.uid = this.uid;
-	}
-}
-
 /**
  * Only available on the server and when compiling with the `server` option.
  * Takes a component and returns an object with `body` and `head` properties on it, which you can use to populate the HTML when server-rendering your app.

From 98508df92b23e8e6352e27c93431af3555c07c4c Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Apr 2025 19:06:18 -0400
Subject: [PATCH 08/10] only export things that should be available on $

---
 packages/svelte/src/internal/server/dev.js    |  2 +-
 packages/svelte/src/internal/server/index.js  | 70 ++-----------------
 .../svelte/src/internal/server/payload.js     | 64 +++++++++++++++++
 packages/svelte/src/internal/shared/errors.js |  4 +-
 4 files changed, 71 insertions(+), 69 deletions(-)
 create mode 100644 packages/svelte/src/internal/server/payload.js

diff --git a/packages/svelte/src/internal/server/dev.js b/packages/svelte/src/internal/server/dev.js
index 2df8e1133310..34849196b7b6 100644
--- a/packages/svelte/src/internal/server/dev.js
+++ b/packages/svelte/src/internal/server/dev.js
@@ -6,7 +6,7 @@ import {
 } from '../../html-tree-validation.js';
 import { current_component } from './context.js';
 import { invalid_snippet_arguments } from '../shared/errors.js';
-import { Payload } from './index.js';
+import { Payload } from './payload.js';
 
 /**
  * @typedef {{
diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index 4400aca41882..97728b5b3318 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -17,67 +17,13 @@ import { EMPTY_COMMENT, BLOCK_CLOSE, BLOCK_OPEN } from './hydration.js';
 import { validate_store } from '../shared/validate.js';
 import { is_boolean_attribute, is_raw_text_element, is_void } from '../../utils.js';
 import { reset_elements } from './dev.js';
+import { Payload } from './payload.js';
 
 // https://html.spec.whatwg.org/multipage/syntax.html#attributes-2
 // https://infra.spec.whatwg.org/#noncharacter
 const INVALID_ATTR_NAME_CHAR_REGEX =
 	/[\s'">/=\u{FDD0}-\u{FDEF}\u{FFFE}\u{FFFF}\u{1FFFE}\u{1FFFF}\u{2FFFE}\u{2FFFF}\u{3FFFE}\u{3FFFF}\u{4FFFE}\u{4FFFF}\u{5FFFE}\u{5FFFF}\u{6FFFE}\u{6FFFF}\u{7FFFE}\u{7FFFF}\u{8FFFE}\u{8FFFF}\u{9FFFE}\u{9FFFF}\u{AFFFE}\u{AFFFF}\u{BFFFE}\u{BFFFF}\u{CFFFE}\u{CFFFF}\u{DFFFE}\u{DFFFF}\u{EFFFE}\u{EFFFF}\u{FFFFE}\u{FFFFF}\u{10FFFE}\u{10FFFF}]/u;
 
-class Payload {
-	/** @type {Set<{ hash: string; code: string }>} */
-	css = new Set();
-	out = '';
-	uid = () => '';
-
-	head = {
-		/** @type {Set<{ hash: string; code: string }>} */
-		css: new Set(),
-		title: '',
-		out: '',
-		uid: () => ''
-	};
-
-	constructor(id_prefix = '') {
-		this.uid = props_id_generator(id_prefix);
-		this.head.uid = this.uid;
-	}
-}
-
-/**
- * Used in legacy mode to handle bindings
- * @param {Payload} to_copy
- * @returns {Payload}
- */
-export function copy_payload({ out, css, head, uid }) {
-	const payload = new Payload();
-
-	payload.out = out;
-	payload.css = new Set(css);
-	payload.uid = uid;
-
-	payload.head = {
-		title: head.title,
-		out: head.out,
-		css: new Set(head.css),
-		uid: head.uid
-	};
-
-	return payload;
-}
-
-/**
- * Assigns second payload to first
- * @param {Payload} p1
- * @param {Payload} p2
- * @returns {void}
- */
-export function assign_payload(p1, p2) {
-	p1.out = p2.out;
-	p1.css = p2.css;
-	p1.head = p2.head;
-	p1.uid = p2.uid;
-}
-
 /**
  * @param {Payload} payload
  * @param {string} tag
@@ -111,16 +57,6 @@ export function element(payload, tag, attributes_fn = noop, children_fn = noop)
  */
 export let on_destroy = [];
 
-/**
- * Creates an ID generator
- * @param {string} prefix
- * @returns {() => string}
- */
-function props_id_generator(prefix) {
-	let uid = 1;
-	return () => `${prefix}s${uid++}`;
-}
-
 /**
  * Only available on the server and when compiling with the `server` option.
  * Takes a component and returns an object with `body` and `head` properties on it, which you can use to populate the HTML when server-rendering your app.
@@ -553,7 +489,7 @@ export function props_id(payload) {
 	return uid;
 }
 
-export { attr, clsx, Payload };
+export { attr, clsx };
 
 export { html } from './blocks/html.js';
 
@@ -561,6 +497,8 @@ export { push, pop } from './context.js';
 
 export { push_element, pop_element, validate_snippet_args } from './dev.js';
 
+export { assign_payload, copy_payload } from './payload.js';
+
 export { snapshot } from '../shared/clone.js';
 
 export { fallback } from '../shared/utils.js';
diff --git a/packages/svelte/src/internal/server/payload.js b/packages/svelte/src/internal/server/payload.js
new file mode 100644
index 000000000000..03bcaf492ea9
--- /dev/null
+++ b/packages/svelte/src/internal/server/payload.js
@@ -0,0 +1,64 @@
+export class Payload {
+	/** @type {Set<{ hash: string; code: string }>} */
+	css = new Set();
+	out = '';
+	uid = () => '';
+
+	head = {
+		/** @type {Set<{ hash: string; code: string }>} */
+		css: new Set(),
+		title: '',
+		out: '',
+		uid: () => ''
+	};
+
+	constructor(id_prefix = '') {
+		this.uid = props_id_generator(id_prefix);
+		this.head.uid = this.uid;
+	}
+}
+
+/**
+ * Used in legacy mode to handle bindings
+ * @param {Payload} to_copy
+ * @returns {Payload}
+ */
+export function copy_payload({ out, css, head, uid }) {
+	const payload = new Payload();
+
+	payload.out = out;
+	payload.css = new Set(css);
+	payload.uid = uid;
+
+	payload.head = {
+		title: head.title,
+		out: head.out,
+		css: new Set(head.css),
+		uid: head.uid
+	};
+
+	return payload;
+}
+
+/**
+ * Assigns second payload to first
+ * @param {Payload} p1
+ * @param {Payload} p2
+ * @returns {void}
+ */
+export function assign_payload(p1, p2) {
+	p1.out = p2.out;
+	p1.css = p2.css;
+	p1.head = p2.head;
+	p1.uid = p2.uid;
+}
+
+/**
+ * Creates an ID generator
+ * @param {string} prefix
+ * @returns {() => string}
+ */
+function props_id_generator(prefix) {
+	let uid = 1;
+	return () => `${prefix}s${uid++}`;
+}
diff --git a/packages/svelte/src/internal/shared/errors.js b/packages/svelte/src/internal/shared/errors.js
index 7d31d6e91049..2e89dc1ad109 100644
--- a/packages/svelte/src/internal/shared/errors.js
+++ b/packages/svelte/src/internal/shared/errors.js
@@ -18,12 +18,12 @@ export function invalid_default_snippet() {
 }
 
 /**
- * A snippet function was passed invalid arguments. A snippet function should only be called via `{@render ...}`
+ * A snippet function was passed invalid arguments. Snippets should only be instantiated via `{@render ...}`
  * @returns {never}
  */
 export function invalid_snippet_arguments() {
 	if (DEV) {
-		const error = new Error(`invalid_snippet_arguments\nA snippet function was passed invalid arguments. A snippet function should only be called via \`{@render ...}\`\nhttps://svelte.dev/e/invalid_snippet_arguments`);
+		const error = new Error(`invalid_snippet_arguments\nA snippet function was passed invalid arguments. Snippets should only be instantiated via \`{@render ...}\`\nhttps://svelte.dev/e/invalid_snippet_arguments`);
 
 		error.name = 'Svelte error';
 		throw error;

From e3064596e2ecec1639f6c02deaf149228b388f80 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Apr 2025 19:06:24 -0400
Subject: [PATCH 09/10] tweak message

---
 documentation/docs/98-reference/.generated/shared-errors.md | 2 +-
 packages/svelte/messages/shared-errors/errors.md            | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/documentation/docs/98-reference/.generated/shared-errors.md b/documentation/docs/98-reference/.generated/shared-errors.md
index 09652c7d0cb7..4c81d7b89452 100644
--- a/documentation/docs/98-reference/.generated/shared-errors.md
+++ b/documentation/docs/98-reference/.generated/shared-errors.md
@@ -33,7 +33,7 @@ Here, `List.svelte` is using `{@render children(item)` which means it expects `P
 ### invalid_snippet_arguments
 
 ```
-A snippet function was passed invalid arguments. A snippet function should only be called via `{@render ...}`
+A snippet function was passed invalid arguments. Snippets should only be instantiated via `{@render ...}`
 ```
 
 ### lifecycle_outside_component
diff --git a/packages/svelte/messages/shared-errors/errors.md b/packages/svelte/messages/shared-errors/errors.md
index 6367ce726e4e..20f3d193d928 100644
--- a/packages/svelte/messages/shared-errors/errors.md
+++ b/packages/svelte/messages/shared-errors/errors.md
@@ -28,7 +28,7 @@ Here, `List.svelte` is using `{@render children(item)` which means it expects `P
 
 ## invalid_snippet_arguments
 
-> A snippet function was passed invalid arguments. A snippet function should only be called via `{@render ...}`
+> A snippet function was passed invalid arguments. Snippets should only be instantiated via `{@render ...}`
 
 ## lifecycle_outside_component
 

From e72ac0f5005d8c4f668ea21262ed731d2a3cbfdf Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Apr 2025 19:45:32 -0400
Subject: [PATCH 10/10] fix

---
 packages/svelte/src/internal/server/blocks/snippet.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/svelte/src/internal/server/blocks/snippet.js b/packages/svelte/src/internal/server/blocks/snippet.js
index 466de1926adc..9e96ae34305d 100644
--- a/packages/svelte/src/internal/server/blocks/snippet.js
+++ b/packages/svelte/src/internal/server/blocks/snippet.js
@@ -1,5 +1,5 @@
 /** @import { Snippet } from 'svelte' */
-/** @import { Payload } from '../index' */
+/** @import { Payload } from '../payload' */
 /** @import { Getters } from '#shared' */
 
 /**