fix: create `<svelte:element>` instances with the correct namespace (#10006)

Infer namespace from parents where possible, and do a runtime-best-effort where it's not statically known
fixes #9645

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>

.github/workflows/ci.yml

@@ -55,6 +55,8 @@ jobs:
       - name: type check
         run: pnpm check
       - name: lint
+        if: (${{ success() }} || ${{ failure() }}) # ensures this step runs even if previous steps fail (avoids multiple runs uncovering different issues at different steps)
         run: pnpm lint
       - name: build and check generated types
+        if: (${{ success() }} || ${{ failure() }}) # ensures this step runs even if previous steps fail
         run: pnpm build && { [ "`git status --porcelain=v1`" == "" ] || (echo "Generated types have changed — please regenerate types locally and commit the changes after you have reviewed them"; git diff; exit 1); }

packages/svelte/src/compiler/phases/1-parse/read/options.js

@@ -1,3 +1,4 @@
+import { namespace_svg } from '../../../../constants.js';
 import { error } from '../../../errors.js';
 
 const regex_valid_tag_name = /^[a-zA-Z][a-zA-Z0-9]*-[a-zA-Z0-9-]+$/;
@@ -156,7 +157,7 @@ export default function read_options(node) {
 					error(attribute, 'invalid-svelte-option-namespace');
 				}
 
-				if (value === 'http://www.w3.org/2000/svg') {
+				if (value === namespace_svg) {
 					component_options.namespace = 'svg';
 				} else if (value === 'html' || value === 'svg' || value === 'foreign') {
 					component_options.namespace = value;

packages/svelte/src/compiler/phases/1-parse/state/element.js

@@ -139,7 +139,10 @@ export default function tag(parser) {
 					name,
 					attributes: [],
 					fragment: create_fragment(true),
-					parent: null
+					parent: null,
+					metadata: {
+						svg: false
+					}
 				};
 
 	parser.allow_whitespace();

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -20,7 +20,7 @@ import { warn } from '../../warnings.js';
 import check_graph_for_cycles from './utils/check_graph_for_cycles.js';
 import { regex_starts_with_newline } from '../patterns.js';
 import { create_attribute, is_element_node } from '../nodes.js';
-import { DelegatedEvents } from '../../../constants.js';
+import { DelegatedEvents, namespace_svg } from '../../../constants.js';
 import { should_proxy_or_freeze } from '../3-transform/client/utils.js';
 
 /**
@@ -1104,8 +1104,47 @@ const common_visitors = {
 
 		context.state.analysis.elements.push(node);
 	},
-	SvelteElement(node, { state }) {
-		state.analysis.elements.push(node);
+	SvelteElement(node, context) {
+		context.state.analysis.elements.push(node);
+
+		if (
+			context.state.options.namespace !== 'foreign' &&
+			node.tag.type === 'Literal' &&
+			typeof node.tag.value === 'string' &&
+			SVGElements.includes(node.tag.value)
+		) {
+			node.metadata.svg = true;
+			return;
+		}
+
+		for (const attribute of node.attributes) {
+			if (attribute.type === 'Attribute') {
+				if (attribute.name === 'xmlns' && is_text_attribute(attribute)) {
+					node.metadata.svg = attribute.value[0].data === namespace_svg;
+					return;
+				}
+			}
+		}
+
+		for (let i = context.path.length - 1; i >= 0; i--) {
+			const ancestor = context.path[i];
+			if (
+				ancestor.type === 'Component' ||
+				ancestor.type === 'SvelteComponent' ||
+				ancestor.type === 'SvelteFragment' ||
+				ancestor.type === 'SnippetBlock'
+			) {
+				// Inside a slot or a snippet -> this resets the namespace, so we can't determine it
+				return;
+			}
+			if (ancestor.type === 'SvelteElement' || ancestor.type === 'RegularElement') {
+				node.metadata.svg =
+					ancestor.type === 'RegularElement' && ancestor.name === 'foreignObject'
+						? false
+						: ancestor.metadata.svg;
+				return;
+			}
+		}
 	}
 };
 

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -9,7 +9,7 @@ import {
 import { binding_properties } from '../../../bindings.js';
 import {
 	clean_nodes,
-	determine_element_namespace,
+	determine_namespace_for_children,
 	escape_html,
 	infer_namespace
 } from '../../utils.js';
@@ -43,11 +43,7 @@ import { sanitize_template_string } from '../../../../utils/sanitize_template_st
  */
 function get_attribute_name(element, attribute, context) {
 	let name = attribute.name;
-	if (
-		element.type === 'RegularElement' &&
-		!element.metadata.svg &&
-		context.state.metadata.namespace !== 'foreign'
-	) {
+	if (!element.metadata.svg && context.state.metadata.namespace !== 'foreign') {
 		name = name.toLowerCase();
 		if (name in AttributeAliases) {
 			name = AttributeAliases[name];
@@ -1854,7 +1850,7 @@ export const template_visitors = {
 		const metadata = context.state.metadata;
 		const child_metadata = {
 			...context.state.metadata,
-			namespace: determine_element_namespace(node, context.state.metadata.namespace, context.path)
+			namespace: determine_namespace_for_children(node, context.state.metadata.namespace)
 		};
 
 		context.state.template.push(`<${node.name}`);
@@ -2079,9 +2075,6 @@ export const template_visitors = {
 		/** @type {import('estree').ExpressionStatement[]} */
 		const lets = [];
 
-		/** @type {string | null} */
-		let namespace = null;
-
 		// Create a temporary context which picks up the init/update statements.
 		// They'll then be added to the function parameter of $.element
 		const element_id = b.id(context.state.scope.generate('$$element'));
@@ -2102,9 +2095,6 @@ export const template_visitors = {
 		for (const attribute of node.attributes) {
 			if (attribute.type === 'Attribute') {
 				attributes.push(attribute);
-				if (attribute.name === 'xmlns' && is_text_attribute(attribute)) {
-					namespace = attribute.value[0].data;
-				}
 			} else if (attribute.type === 'SpreadAttribute') {
 				attributes.push(attribute);
 			} else if (attribute.type === 'ClassDirective') {
@@ -2153,19 +2143,32 @@ export const template_visitors = {
 			}
 		}
 		inner.push(...inner_context.state.after_update);
-		inner.push(...create_block(node, 'dynamic_element', node.fragment.nodes, context));
+		inner.push(
+			...create_block(node, 'dynamic_element', node.fragment.nodes, {
+				...context,
+				state: {
+					...context.state,
+					metadata: {
+						...context.state.metadata,
+						namespace: determine_namespace_for_children(node, context.state.metadata.namespace)
+					}
+				}
+			})
+		);
 		context.state.after_update.push(
 			b.stmt(
 				b.call(
 					'$.element',
 					context.state.node,
 					get_tag,
+					node.metadata.svg === true
+						? b.true
+						: node.metadata.svg === false
+							? b.false
+							: b.literal(null),
 					inner.length === 0
 						? /** @type {any} */ (undefined)
-						: b.arrow([element_id, b.id('$$anchor')], b.block(inner)),
-					namespace === 'http://www.w3.org/2000/svg'
-						? b.literal(true)
-						: /** @type {any} */ (undefined)
+						: b.arrow([element_id, b.id('$$anchor')], b.block(inner))
 				)
 			)
 		);

packages/svelte/src/compiler/phases/3-transform/server/transform-server.js

@@ -15,7 +15,7 @@ import {
 } from '../../constants.js';
 import {
 	clean_nodes,
-	determine_element_namespace,
+	determine_namespace_for_children,
 	escape_html,
 	infer_namespace,
 	transform_inspect_rune
@@ -482,11 +482,7 @@ function serialize_set_binding(node, context, fallback) {
  */
 function get_attribute_name(element, attribute, context) {
 	let name = attribute.name;
-	if (
-		element.type === 'RegularElement' &&
-		!element.metadata.svg &&
-		context.state.metadata.namespace !== 'foreign'
-	) {
+	if (!element.metadata.svg && context.state.metadata.namespace !== 'foreign') {
 		name = name.toLowerCase();
 		// don't lookup boolean aliases here, the server runtime function does only
 		// check for the lowercase variants of boolean attributes
@@ -761,10 +757,10 @@ function serialize_element_spread_attributes(
 	}
 
 	const lowercase_attributes =
-		element.type !== 'RegularElement' || element.metadata.svg || is_custom_element_node(element)
+		element.metadata.svg || (element.type === 'RegularElement' && is_custom_element_node(element))
 			? b.false
 			: b.true;
-	const is_svg = element.type === 'RegularElement' && element.metadata.svg ? b.true : b.false;
+	const is_svg = element.metadata.svg ? b.true : b.false;
 	/** @type {import('estree').Expression[]} */
 	const args = [
 		b.array(values),
@@ -1165,7 +1161,7 @@ const template_visitors = {
 	RegularElement(node, context) {
 		const metadata = {
 			...context.state.metadata,
-			namespace: determine_element_namespace(node, context.state.metadata.namespace, context.path)
+			namespace: determine_namespace_for_children(node, context.state.metadata.namespace)
 		};
 
 		context.state.template.push(t_string(`<${node.name}`));
@@ -1255,11 +1251,16 @@ const template_visitors = {
 			context.state.init.push(b.stmt(b.call('$.validate_dynamic_element_tag', b.thunk(tag))));
 		}
 
+		const metadata = {
+			...context.state.metadata,
+			namespace: determine_namespace_for_children(node, context.state.metadata.namespace)
+		};
 		/** @type {import('./types').ComponentContext} */
 		const inner_context = {
 			...context,
 			state: {
 				...context.state,
+				metadata,
 				template: [],
 				init: []
 			}
@@ -1276,7 +1277,10 @@ const template_visitors = {
 		inner_context.state.template.push(t_string('>'));
 
 		const before = serialize_template(inner_context.state.template);
-		const main = create_block(node, node.fragment.nodes, context);
+		const main = create_block(node, node.fragment.nodes, {
+			...context,
+			state: { ...context.state, metadata }
+		});
 		const after = serialize_template([
 			t_expression(inner_id),
 			t_string('</'),

packages/svelte/src/compiler/phases/3-transform/utils.js

@@ -188,7 +188,7 @@ export function clean_nodes(
 }
 
 /**
- * Infers the new namespace for the children of a node.
+ * Infers the namespace for the children of a node that should be used when creating the `$.template(...)`.
  * @param {import('#compiler').Namespace} namespace
  * @param {import('#compiler').SvelteNode} parent
  * @param {import('#compiler').SvelteNode[]} nodes
@@ -201,19 +201,28 @@ export function infer_namespace(namespace, parent, nodes, path) {
 				path.at(-1)
 			: parent;
 
-	if (
-		namespace !== 'foreign' &&
+	if (namespace !== 'foreign') {
+		if (parent_node?.type === 'RegularElement' && parent_node.name === 'foreignObject') {
+			return 'html';
+		}
+
+		if (parent_node?.type === 'RegularElement' || parent_node?.type === 'SvelteElement') {
+			return parent_node.metadata.svg ? 'svg' : 'html';
+		}
+
 		// Re-evaluate the namespace inside slot nodes that reset the namespace
-		(parent_node === undefined ||
+		if (
+			parent_node === undefined ||
 			parent_node.type === 'Root' ||
 			parent_node.type === 'Component' ||
 			parent_node.type === 'SvelteComponent' ||
 			parent_node.type === 'SvelteFragment' ||
-			parent_node.type === 'SnippetBlock')
-	) {
-		const new_namespace = check_nodes_for_namespace(nodes, 'keep');
-		if (new_namespace !== 'keep' && new_namespace !== 'maybe_html') {
-			namespace = new_namespace;
+			parent_node.type === 'SnippetBlock'
+		) {
+			const new_namespace = check_nodes_for_namespace(nodes, 'keep');
+			if (new_namespace !== 'keep' && new_namespace !== 'maybe_html') {
+				return new_namespace;
+			}
 		}
 	}
 
@@ -229,7 +238,7 @@ export function infer_namespace(namespace, parent, nodes, path) {
  */
 function check_nodes_for_namespace(nodes, namespace) {
 	for (const node of nodes) {
-		if (node.type === 'RegularElement') {
+		if (node.type === 'RegularElement' || node.type === 'SvelteElement') {
 			if (!node.metadata.svg) {
 				namespace = 'html';
 				break;
@@ -279,36 +288,21 @@ function check_nodes_for_namespace(nodes, namespace) {
 }
 
 /**
- * @param {import('#compiler').RegularElement} node
+ * Determines the namespace the children of this node are in.
+ * @param {import('#compiler').RegularElement | import('#compiler').SvelteElement} node
  * @param {import('#compiler').Namespace} namespace
- * @param {import('#compiler').SvelteNode[]} path
  * @returns {import('#compiler').Namespace}
  */
-export function determine_element_namespace(node, namespace, path) {
-	if (namespace !== 'foreign') {
-		let parent = path.at(-1);
-		if (parent?.type === 'Fragment') {
-			parent = path.at(-2);
-		}
+export function determine_namespace_for_children(node, namespace) {
+	if (namespace === 'foreign') {
+		return namespace;
+	}
 
-		if (node.name === 'foreignObject') {
-			return 'html';
-		} else if (
-			namespace !== 'svg' ||
-			parent?.type === 'Component' ||
-			parent?.type === 'SvelteComponent' ||
-			parent?.type === 'SvelteFragment' ||
-			parent?.type === 'SnippetBlock'
-		) {
-			if (node.metadata.svg) {
-				return 'svg';
-			} else {
-				return 'html';
-			}
-		}
+	if (node.name === 'foreignObject') {
+		return 'html';
 	}
 
-	return namespace;
+	return node.metadata.svg ? 'svg' : 'html';
 }
 
 /**

packages/svelte/src/compiler/types/template.d.ts

@@ -308,6 +308,13 @@ export interface SvelteElement extends BaseElement {
 	type: 'SvelteElement';
 	name: 'svelte:element';
 	tag: Expression;
+	metadata: {
+		/**
+		 * `true`/`false` if this is definitely (not) an svg element.
+		 * `null` means we can't know statically.
+		 */
+		svg: boolean | null;
+	};
 }
 
 export interface SvelteFragment extends BaseElement {

packages/svelte/src/constants.js

@@ -85,3 +85,6 @@ export const DOMBooleanAttributes = [
 	'seamless',
 	'selected'
 ];
+
+export const namespace_svg = 'http://www.w3.org/2000/svg';
+export const namespace_html = 'http://www.w3.org/1999/xhtml';

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

@@ -19,7 +19,13 @@ import {
 	create_dynamic_component_block,
 	create_snippet_block
 } from './block.js';
-import { PassiveDelegatedEvents, DelegatedEvents, AttributeAliases } from '../../constants.js';
+import {
+	PassiveDelegatedEvents,
+	DelegatedEvents,
+	AttributeAliases,
+	namespace_svg,
+	namespace_html
+} from '../../constants.js';
 import { create_fragment_from_html, insert, reconcile_html, remove } from './reconciler.js';
 import {
 	render_effect,
@@ -1595,11 +1601,11 @@ function swap_block_dom(block, from, to) {
 /**
  * @param {Comment} anchor_node
  * @param {() => string} tag_fn
+ * @param {boolean | null} is_svg `null` == not statically known
  * @param {undefined | ((element: Element, anchor: Node) => void)} render_fn
- * @param {any} is_svg
  * @returns {void}
  */
-export function element(anchor_node, tag_fn, render_fn, is_svg = false) {
+export function element(anchor_node, tag_fn, is_svg, render_fn) {
 	const block = create_dynamic_element_block();
 	hydrate_block_anchor(anchor_node);
 	let has_mounted = false;
@@ -1607,7 +1613,7 @@ export function element(anchor_node, tag_fn, render_fn, is_svg = false) {
 	/** @type {string} */
 	let tag;
 
-	/** @type {null | HTMLElement | SVGElement} */
+	/** @type {null | Element} */
 	let element = null;
 	const element_effect = render_effect(
 		() => {
@@ -1623,11 +1629,20 @@ export function element(anchor_node, tag_fn, render_fn, is_svg = false) {
 	// Managed effect
 	const render_effect_signal = render_effect(
 		() => {
+			// We try our best infering the namespace in case it's not possible to determine statically,
+			// but on the first render on the client (without hydration) the parent will be undefined,
+			// since the anchor is not attached to its parent / the dom yet.
+			const ns =
+				is_svg || tag === 'svg'
+					? namespace_svg
+					: is_svg === false || anchor_node.parentElement?.tagName === 'foreignObject'
+						? null
+						: anchor_node.parentElement?.namespaceURI ?? null;
 			const next_element = tag
 				? current_hydration_fragment !== null
-					? /** @type {HTMLElement | SVGElement} */ (current_hydration_fragment[0])
-					: is_svg
-						? document.createElementNS('http://www.w3.org/2000/svg', tag)
+					? /** @type {Element} */ (current_hydration_fragment[0])
+					: ns
+						? document.createElementNS(ns, tag)
 						: document.createElement(tag)
 				: null;
 			const prev_element = element;
@@ -2098,7 +2113,7 @@ export function cssProps(anchor, is_html, props, component) {
 			tag = document.createElement('div');
 			tag.style.display = 'contents';
 		} else {
-			tag = document.createElementNS('http://www.w3.org/2000/svg', 'g');
+			tag = document.createElementNS(namespace_svg, 'g');
 		}
 		insert(tag, null, anchor);
 		component_anchor = empty();
@@ -2629,7 +2644,7 @@ export function spread_dynamic_element_attributes(node, prev, attrs, css_hash) {
 			/** @type {Element & ElementCSSInlineStyle} */ (node),
 			prev,
 			attrs,
-			node.namespaceURI !== 'http://www.w3.org/2000/svg',
+			node.namespaceURI !== namespace_svg,
 			css_hash
 		);
 	}

packages/svelte/src/internal/index.js

@@ -40,15 +40,12 @@ export {
 	unwrap,
 	freeze
 } from './client/runtime.js';
-
 export * from './client/each.js';
 export * from './client/render.js';
 export * from './client/validate.js';
 export { raf } from './client/timing.js';
 export { proxy, readonly, unstate } from './client/proxy.js';
-
 export { create_custom_element } from './client/custom-element.js';
-
 export {
 	child,
 	child_frag,

packages/svelte/tests/runtime-legacy/samples/dynamic-element-svg-implicit-namespace/_config.js

@@ -0,0 +1,16 @@
+import { test } from '../../test';
+
+export default test({
+	// This is skipped for now, because it's not clear how to make this work on client-side initial run:
+	// The anchor isn't connected to its parent at the time we can do a runtime check for the namespace, and we
+	// need the parent for this check. (this didn't work in Svelte 4 either)
+	skip: true,
+	html: '<svg><path></path></svg>',
+
+	test({ assert, target }) {
+		const svg = target.querySelector('svg');
+		const rect = target.querySelector('path');
+		assert.equal(svg?.namespaceURI, 'http://www.w3.org/2000/svg');
+		assert.equal(rect?.namespaceURI, 'http://www.w3.org/2000/svg');
+	}
+});

packages/svelte/tests/runtime-legacy/samples/dynamic-element-svg-implicit-namespace/main.svelte

@@ -0,0 +1,10 @@
+<script>
+	// ensure these are treated as dynamic, despite whatever
+	// optimisations we might apply
+	export let svg = 'svg';
+	export let path = 'path';
+</script>
+
+<svelte:element this={svg}>
+	<svelte:element this={path}></svelte:element>
+</svelte:element>

packages/svelte/tests/runtime-legacy/samples/dynamic-element-svg-inherit-namespace/_config.js

@@ -0,0 +1,20 @@
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target }) {
+		const [svg1, svg2] = target.querySelectorAll('svg');
+		const [path1, path2] = target.querySelectorAll('path');
+		const [fO1, fO2] = target.querySelectorAll('foreignObject');
+		const [span1, span2] = target.querySelectorAll('span');
+
+		assert.equal(svg1.namespaceURI, 'http://www.w3.org/2000/svg');
+		assert.equal(path1.namespaceURI, 'http://www.w3.org/2000/svg');
+
+		assert.equal(svg2.namespaceURI, 'http://www.w3.org/2000/svg');
+		assert.equal(path2.namespaceURI, 'http://www.w3.org/2000/svg');
+		assert.equal(fO1.namespaceURI, 'http://www.w3.org/2000/svg');
+		assert.equal(span1.namespaceURI, 'http://www.w3.org/1999/xhtml');
+		assert.equal(fO2.namespaceURI, 'http://www.w3.org/2000/svg');
+		assert.equal(span2.namespaceURI, 'http://www.w3.org/1999/xhtml');
+	}
+});

packages/svelte/tests/runtime-legacy/samples/dynamic-element-svg-inherit-namespace/main.svelte

@@ -0,0 +1,22 @@
+<script>
+	const iconNode = [["path", { "d": "M21 12a9 9 0 1 1-6.219-8.56" }]];
+</script>
+
+<svg>
+	{#each iconNode as [tag, attrs]}
+		<svelte:element this={tag} {...attrs}/>
+	{/each}
+</svg>
+
+<svg>
+	<svelte:element this="path">
+		<foreignObject>
+			<svelte:element this="span">ok</svelte:element>
+		</foreignObject>
+		<foreignObject>
+			{#if true}
+				<svelte:element this="span">ok</svelte:element>
+			{/if}
+		</foreignObject>
+	</svelte:element>
+</svg>

packages/svelte/tests/snapshot/samples/svelte-element/_expected/client/index.svelte.js

@@ -11,7 +11,7 @@ export default function Svelte_element($$anchor, $$props) {
 	var fragment = $.comment($$anchor);
 	var node = $.child_frag(fragment);
 
-	$.element(node, tag);
+	$.element(node, tag, false);
 	$.close_frag($$anchor, fragment);
 	$.pop();
 }

packages/svelte/types/index.d.ts

@@ -1342,6 +1342,13 @@ declare module 'svelte/compiler' {
 		type: 'SvelteElement';
 		name: 'svelte:element';
 		tag: Expression;
+		metadata: {
+			/**
+			 * `true`/`false` if this is definitely (not) an svg element.
+			 * `null` means we can't know statically.
+			 */
+			svg: boolean | null;
+		};
 	}
 
 	interface SvelteFragment extends BaseElement {