[fix] call attribute bindings for custom element if <svelte:element> render custom element

src/compiler/compile/render_dom/wrappers/Element/index.ts

@@ -803,15 +803,31 @@ export default class ElementWrapper extends Wrapper {
 
 		const fn = this.node.namespace === namespaces.svg ? x`@set_svg_attributes` : x`@set_attributes`;
 
-		block.chunks.hydrate.push(
-			b`${fn}(${this.var}, ${data});`
-		);
+		if (this.node.is_dynamic_element) {
+			// call attribute bindings for custom element if tag is custom element
+			const tag = this.node.tag_expr.manipulate(block);
+			const attr_update = b`
+				if (/-/.test(${tag})) {
+					@set_custom_element_data_map(${this.var}, ${data});
+				} else {
+					${fn}(${this.var}, ${data});
+				}`;
+			block.chunks.hydrate.push(attr_update);
+			block.chunks.update.push(b`
+				${data} = @get_spread_update(${levels}, [${updates}]);
+				${attr_update}`
+			);
+		} else {
+			block.chunks.hydrate.push(
+				b`${fn}(${this.var}, ${data});`
+			);
 
-		block.chunks.update.push(b`
-			${fn}(${this.var}, ${data} = @get_spread_update(${levels}, [
-				${updates}
-			]));
-		`);
+			block.chunks.update.push(b`
+				${fn}(${this.var}, ${data} = @get_spread_update(${levels}, [
+					${updates}
+				]));
+			`);
+		}
 
 		// handle edge cases for elements
 		if (this.node.name === 'select') {

src/runtime/internal/dom.ts

@@ -310,6 +310,12 @@ export function set_svg_attributes(node: Element & ElementCSSInlineStyle, attrib
 	}
 }
 
+export function set_custom_element_data_map(node, data_map: Record<string, unknown>) {
+	Object.keys(data_map).forEach((key) => {
+		set_custom_element_data(node, key, data_map[key]);
+	});
+}
+
 export function set_custom_element_data(node, prop, value) {
 	if (prop in node) {
 		node[prop] = typeof node[prop] === 'boolean' && value === '' ? true : value;

test/runtime-puppeteer/samples/dynamic-element-custom-element/_config.js

@@ -0,0 +1,47 @@
+export default {
+	skip_if_ssr: true,
+	props: {
+		tag: 'my-custom-element',
+		name: null
+	},
+	html: `
+		<my-custom-element id="a">Hello null!</my-custom-element>
+		<my-custom-element id="b">Hello null!</my-custom-element>
+	`,
+
+	test({ assert, component, target }) {
+		component.name = undefined;
+		assert.htmlEqual(
+			target.innerHTML,
+			`<my-custom-element id="a">Hello undefined!</my-custom-element>
+			 <my-custom-element id="b">Hello undefined!</my-custom-element>`
+		);
+
+		component.name = 'foo';
+		assert.htmlEqual(
+			target.innerHTML,
+			`<my-custom-element id="a">Hello foo!</my-custom-element>
+			 <my-custom-element id="b">Hello foo!</my-custom-element>`
+		);
+
+		component.tag = null;
+		assert.htmlEqual(
+			target.innerHTML,
+			'<my-custom-element id="b">Hello foo!</my-custom-element>'
+		);
+
+		component.tag = 'div';
+		assert.htmlEqual(
+			target.innerHTML,
+			`<div name="foo" id="a"></div>
+			 <my-custom-element id="b">Hello foo!</my-custom-element>`
+		);
+
+		component.tag = 'my-custom-element';
+		assert.htmlEqual(
+			target.innerHTML,
+			`<my-custom-element id="a">Hello foo!</my-custom-element>
+			 <my-custom-element id="b">Hello foo!</my-custom-element>`
+		);
+	}
+};

test/runtime-puppeteer/samples/dynamic-element-custom-element/main.svelte

@@ -0,0 +1,32 @@
+<script>
+	class MyCustomElement extends HTMLElement {
+		constructor() {
+			super();
+			this._name = null;
+		}
+
+		/**
+		 * @param {string} name
+		 */
+		set name(name) {
+			this._name = name;
+			this.render();
+		}
+
+		connectedCallback() {
+			this.render();
+		}
+
+		render() {
+			this.innerHTML = "Hello " + this._name + "!";
+		}
+	}
+
+	window.customElements.define("my-custom-element", MyCustomElement);
+
+	export let tag;
+	export let name;
+</script>
+
+<svelte:element this="{tag}" {name} id="a" />
+<my-custom-element {name} id="b" />