Merge pull request #847 from sveltejs/gh-827

Don't slot elements inside custom elements

src/generators/dom/preprocess.ts

@@ -2,6 +2,7 @@ import Block from './Block';
 import { trimStart, trimEnd } from '../../utils/trim';
 import { assign } from '../../shared/index.js';
 import getStaticAttributeValue from '../../utils/getStaticAttributeValue';
+import isChildOfComponent from '../shared/utils/isChildOfComponent';
 import { DomGenerator } from './index';
 import { Node } from '../../interfaces';
 import { State } from './interfaces';
@@ -340,7 +341,8 @@ const preprocessors = {
 			});
 		} else {
 			const slot = getStaticAttributeValue(node, 'slot');
-			if (slot) {
+			if (slot && isChildOfComponent(node, generator)) {
+				node.slotted = true;
 				// TODO validate slots — no nesting, no dynamic names...
 				const component = componentStack[componentStack.length - 1];
 				component._slots.add(slot);

src/generators/dom/visitors/Element/Element.ts

@@ -63,7 +63,7 @@ export default function visitElement(
 	const name = childState.parentNode;
 
 	const slot = node.attributes.find((attribute: Node) => attribute.name === 'slot');
-	const parentNode = slot ?
+	const parentNode = node.slotted ?
 		`${componentStack[componentStack.length - 1].var}._slotted.${slot.value[0].data}` : // TODO this looks bonkers
 		state.parentNode;
 

src/generators/server-side-rendering/preprocess.ts

@@ -1,3 +1,5 @@
+import getStaticAttributeValue from '../../utils/getStaticAttributeValue';
+import isChildOfComponent from '../shared/utils/isChildOfComponent';
 import { SsrGenerator } from './index';
 import { Node } from '../../interfaces';
 
@@ -62,6 +64,11 @@ const preprocessors = {
 
 		if (!isComponent) {
 			generator.stylesheet.apply(node, elementStack);
+
+			const slot = getStaticAttributeValue(node, 'slot');
+			if (slot && isChildOfComponent(node, generator)) {
+				node.slotted = true;
+			}
 		}
 
 		if (node.children.length) {
@@ -80,6 +87,8 @@ function preprocessChildren(
 	elementStack: Node[]
 ) {
 	node.children.forEach((child: Node, i: number) => {
+		child.parent = node;
+
 		const preprocessor = preprocessors[child.type];
 		if (preprocessor) preprocessor(generator, child, elementStack);
 	});

src/generators/server-side-rendering/visitors/Element.ts

@@ -47,8 +47,8 @@ export default function visitElement(
 	let openingTag = `<${node.name}`;
 	let textareaContents; // awkward special case
 
+	if (node.slotted) {
 		const slot = node.attributes.find((attribute: Node) => attribute.name === 'slot');
-	if (slot) {
 		const slotName = slot.value[0].data;
 		const appendTarget = generator.appendTargets[generator.appendTargets.length - 1];
 		appendTarget.slotStack.push(slotName);

src/generators/shared/utils/isChildOfComponent.ts

@@ -0,0 +1,13 @@
+import { Node } from '../../../interfaces';
+import Generator from '../../Generator';
+
+export default function isChildOfComponent(node: Node, generator: Generator) {
+	while (node = node.parent) {
+		if (node.type !== 'Element') continue;
+		if (generator.components.has(node.name)) return true;
+		if (/-/.test(node.name)) return false;
+	}
+
+	// TODO do this in validation
+	throw new Error(`Element with a slot='...' attribute must be a descendant of a component or custom element`);
+}

test/runtime/samples/slot-in-custom-element/_config.js

@@ -0,0 +1,7 @@
+export default {
+	html: `
+		<custom-element>
+			<header slot='header'>header header header</header>
+		</custom-element>
+	`
+};

test/runtime/samples/slot-in-custom-element/main.html

@@ -0,0 +1,3 @@
+<custom-element>
+	<header slot='header'>header header header</header>
+</custom-element>