make it possible to render svelte-components inside a shadow dom

site/content/docs/03-run-time.md

@@ -929,7 +929,7 @@ The following initialisation options can be provided:
 
 | option | default | description |
 | --- | --- | --- |
-| `target` | **none** | An `HTMLElement` to render to. This option is required
+| `target` | **none** | An `HTMLElement` or `ShadowRoot` to render to. This option is required
 | `anchor` | `null` | A child of `target` to render the component immediately before
 | `props` | `{}` | An object of properties to supply to the component
 | `context` | `new Map()` | A `Map` of root-level context key-value pairs to supply to the component

src/compiler/compile/render_dom/index.ts

@@ -49,11 +49,8 @@ export default function dom(
 
 	if (should_add_css) {
 		body.push(b`
-			function ${add_css}() {
-				var style = @element("style");
-				style.id = "${component.stylesheet.id}-style";
-				style.textContent = "${styles}";
-				@append(@_document.head, style);
+			function ${add_css}(target) {
+				@append_styles(target, "${component.stylesheet.id}", "${styles}");
 			}
 		`);
 	}
@@ -485,7 +482,7 @@ export default function dom(
 
 					${css.code && b`this.shadowRoot.innerHTML = \`<style>${css.code.replace(/\\/g, '\\\\')}${options.dev ? `\n/*# sourceMappingURL=${css.map.toUrl()} */` : ''}</style>\`;`}
 
-					@init(this, { target: this.shadowRoot, props: ${init_props}, customElement: true }, ${definition}, ${has_create_fragment ? 'create_fragment' : 'null'}, ${not_equal}, ${prop_indexes}, ${dirty});
+					@init(this, { target: this.shadowRoot, props: ${init_props}, customElement: true }, ${definition}, ${has_create_fragment ? 'create_fragment' : 'null'}, ${not_equal}, ${prop_indexes}, null, ${dirty});
 
 					${dev_props_check}
 
@@ -532,12 +529,21 @@ export default function dom(
 			name: options.dev ? '@SvelteComponentDev' : '@SvelteComponent'
 		};
 
+		const optionalParameters = [];
+		if (should_add_css) {
+			optionalParameters.push(add_css);
+		} else if (dirty) {
+			optionalParameters.push(x`null`);
+		}
+		if (dirty) {
+			optionalParameters.push(dirty);
+		}
+
 		const declaration = b`
 			class ${name} extends ${superclass} {
 				constructor(options) {
 					super(${options.dev && 'options'});
-					${should_add_css && b`if (!@_document.getElementById("${component.stylesheet.id}-style")) ${add_css}();`}
-					@init(this, options, ${definition}, ${has_create_fragment ? 'create_fragment' : 'null'}, ${not_equal}, ${prop_indexes}, ${dirty});
+					@init(this, options, ${definition}, ${has_create_fragment ? 'create_fragment' : 'null'}, ${not_equal}, ${prop_indexes}, ${optionalParameters});
 					${options.dev && b`@dispatch_dev("SvelteRegisterComponent", { component: this, tagName: "${name.name}", options, id: create_fragment.name });`}
 
 					${dev_props_check}

src/runtime/internal/Component.ts

@@ -38,6 +38,7 @@ interface T$$ {
 	on_destroy: any[];
 	skip_bound: boolean;
 	on_disconnect: any[];
+	root:Element|ShadowRoot
 }
 
 export function bind(component, name, callback) {
@@ -103,7 +104,7 @@ function make_dirty(component, i) {
 	component.$$.dirty[(i / 31) | 0] |= (1 << (i % 31));
 }
 
-export function init(component, options, instance, create_fragment, not_equal, props, dirty = [-1]) {
+export function init(component, options, instance, create_fragment, not_equal, props, append_styles, dirty = [-1]) {
 	const parent_component = current_component;
 	set_current_component(component);
 
@@ -128,9 +129,12 @@ export function init(component, options, instance, create_fragment, not_equal, p
 		// everything else
 		callbacks: blank_object(),
 		dirty,
-		skip_bound: false
+		skip_bound: false,
+		root: options.target || parent_component.$$.root
 	};
 
+	append_styles && append_styles($$.root);
+
 	let ready = false;
 
 	$$.ctx = instance

src/runtime/internal/dev.ts

@@ -105,7 +105,7 @@ export interface SvelteComponentDev {
 	[accessor: string]: any;
 }
 interface IComponentOptions<Props extends Record<string, any> = Record<string, any>> {
-	target: Element;
+	target: Element|ShadowRoot;
 	anchor?: Element;
 	props?: Props;
 	context?: Map<any, any>;

src/runtime/internal/dom.ts

@@ -112,6 +112,42 @@ function init_hydrate(target: NodeEx) {
 	}
 }
 
+export function append_styles(
+	target: Node,
+	style_sheet_id: string,
+	styles: string
+) {
+	const append_styles_to = get_root_for_styles(target);
+
+	if (!append_styles_to?.getElementById(style_sheet_id)) {
+		const style = element('style');
+		style.id = style_sheet_id;
+		style.textContent = styles;
+		append_stylesheet(append_styles_to, style);
+	}
+}
+
+export function get_root_for_node(node: Node) {
+	if (!node) return document;
+
+	return (node.getRootNode ? node.getRootNode() : node.ownerDocument); // check for getRootNode because IE is still supported
+}
+
+function get_root_for_styles(node: Node) {
+	const root = get_root_for_node(node);
+	return (root as ShadowRoot).host ? root as ShadowRoot : root as Document;
+}
+
+export function append_empty_stylesheet(node: Node) {
+	const style_element = element('style') as HTMLStyleElement;
+	append_stylesheet(get_root_for_styles(node), style_element);
+	return style_element;
+}
+
+function append_stylesheet(node: ShadowRoot | Document, style: HTMLStyleElement) {
+	append((node as Document).head || node, style);
+}
+
 export function append(target: NodeEx, node: NodeEx) {
 	if (is_hydrating) {
 		init_hydrate(target);

src/runtime/internal/style_manager.ts

@@ -1,4 +1,4 @@
-import { element } from './dom';
+import { append_empty_stylesheet, get_root_for_node } from './dom';
 import { raf } from './environment';
 
 interface ExtendedDoc extends Document {
@@ -29,9 +29,9 @@ export function create_rule(node: Element & ElementCSSInlineStyle, a: number, b:
 
 	const rule = keyframes + `100% {${fn(b, 1 - b)}}\n}`;
 	const name = `__svelte_${hash(rule)}_${uid}`;
-	const doc = node.ownerDocument as ExtendedDoc;
+	const doc = get_root_for_node(node) as unknown as ExtendedDoc;
 	active_docs.add(doc);
-	const stylesheet = doc.__svelte_stylesheet || (doc.__svelte_stylesheet = doc.head.appendChild(element('style') as HTMLStyleElement).sheet as CSSStyleSheet);
+	const stylesheet = doc.__svelte_stylesheet || (doc.__svelte_stylesheet = append_empty_stylesheet(node).sheet as CSSStyleSheet);
 	const current_rules = doc.__svelte_rules || (doc.__svelte_rules = {});
 
 	if (!current_rules[name]) {

src/runtime/internal/utils.ts

@@ -79,7 +79,7 @@ export function create_slot(definition, ctx, $$scope, fn) {
 	}
 }
 
-export function get_slot_context(definition, ctx, $$scope, fn) {
+function get_slot_context(definition, ctx, $$scope, fn) {
 	return definition[1] && fn
 		? assign($$scope.ctx.slice(), definition[1](fn(ctx)))
 		: $$scope.ctx;

test/js/samples/collapses-text-around-comments/expected.js

@@ -2,6 +2,7 @@
 import {
 	SvelteComponent,
 	append,
+	append_styles,
 	attr,
 	detach,
 	element,
@@ -13,11 +14,8 @@ import {
 	text
 } from "svelte/internal";
 
-function add_css() {
-	var style = element("style");
-	style.id = "svelte-1a7i8ec-style";
-	style.textContent = "p.svelte-1a7i8ec{color:red}";
-	append(document.head, style);
+function add_css(target) {
+	append_styles(target, "svelte-1a7i8ec", "p.svelte-1a7i8ec{color:red}");
 }
 
 function create_fragment(ctx) {
@@ -58,9 +56,8 @@ function instance($$self, $$props, $$invalidate) {
 class Component extends SvelteComponent {
 	constructor(options) {
 		super();
-		if (!document.getElementById("svelte-1a7i8ec-style")) add_css();
-		init(this, options, instance, create_fragment, safe_not_equal, { foo: 0 });
+		init(this, options, instance, create_fragment, safe_not_equal, { foo: 0 }, add_css);
 	}
 }
 
-export default Component;
+export default Component;

test/js/samples/css-media-query/expected.js

@@ -1,7 +1,7 @@
 /* generated by Svelte vX.Y.Z */
 import {
 	SvelteComponent,
-	append,
+	append_styles,
 	attr,
 	detach,
 	element,
@@ -11,11 +11,8 @@ import {
 	safe_not_equal
 } from "svelte/internal";
 
-function add_css() {
-	var style = element("style");
-	style.id = "svelte-1slhpfn-style";
-	style.textContent = "@media(min-width: 1px){div.svelte-1slhpfn{color:red}}";
-	append(document.head, style);
+function add_css(target) {
+	append_styles(target, "svelte-1slhpfn", "@media(min-width: 1px){div.svelte-1slhpfn{color:red}}");
 }
 
 function create_fragment(ctx) {
@@ -41,9 +38,8 @@ function create_fragment(ctx) {
 class Component extends SvelteComponent {
 	constructor(options) {
 		super();
-		if (!document.getElementById("svelte-1slhpfn-style")) add_css();
-		init(this, options, null, create_fragment, safe_not_equal, {});
+		init(this, options, null, create_fragment, safe_not_equal, {}, add_css);
 	}
 }
 
-export default Component;
+export default Component;

test/js/samples/css-shadow-dom-keyframes/expected.js

@@ -46,7 +46,8 @@ class Component extends SvelteElement {
 			null,
 			create_fragment,
 			safe_not_equal,
-			{}
+			{},
+			null
 		);
 
 		if (options) {
@@ -58,4 +59,4 @@ class Component extends SvelteElement {
 }
 
 customElements.define("custom-element", Component);
-export default Component;
+export default Component;

test/js/samples/reactive-class-optimized/expected.js

@@ -159,4 +159,4 @@ class Component extends SvelteComponent {
 	}
 }
 
-export default Component;
+export default Component;

test/sourcemaps/samples/compile-option-dev/test.js

@@ -4,8 +4,8 @@ const b64dec = s => Buffer.from(s, 'base64').toString();
 
 export async function test({ assert, css,  js }) {
 
-    // We check that the css source map embedded in the js is accurate
-    const match = js.code.match(/\tstyle\.textContent = "(.*?)(?:\\n\/\*# sourceMappingURL=data:(.*?);charset=(.*?);base64,(.*?) \*\/)?";\n/);
+	// We check that the css source map embedded in the js is accurate
+	const match = js.code.match(/\tappend_styles\(target, "svelte-.{6}", "(.*?)(?:\\n\/\*# sourceMappingURL=data:(.*?);charset=(.*?);base64,(.*?) \*\/)?"\);\n/);
 	assert.notEqual(match, null);
 
 	const [mimeType, encoding, cssMapBase64] = match.slice(2);