9 files changed, 258 insertions, 0 deletions
diff --git a/packages/integrations/lit/.gitignore b/packages/integrations/lit/.gitignore
new file mode 100644
index 000000000..40b878db5
--- /dev/null
+++ b/packages/integrations/lit/.gitignore
@@ -0,0 +1 @@
+node_modules/
+\ No newline at end of file
diff --git a/packages/integrations/lit/client-shim.js b/packages/integrations/lit/client-shim.js
new file mode 100644
index 000000000..cab3fe4d9
--- /dev/null
+++ b/packages/integrations/lit/client-shim.js
@@ -0,0 +1,10 @@
+async function polyfill() {
+	const { hydrateShadowRoots } = await import('@webcomponents/template-shadowroot/template-shadowroot.js');
+	hydrateShadowRoots(document.body);
+}
+
+const polyfillCheckEl = new DOMParser().parseFromString(`<p><template shadowroot="open"></template></p>`, 'text/html', { includeShadowRoots: true }).querySelector('p');
+
+if (!polyfillCheckEl || !polyfillCheckEl.shadowRoot) {
+	polyfill();
+}
diff --git a/packages/integrations/lit/client-shim.min.js b/packages/integrations/lit/client-shim.min.js
new file mode 100644
index 000000000..0c6a452d8
--- /dev/null
+++ b/packages/integrations/lit/client-shim.min.js
@@ -0,0 +1,79 @@
+/** @license Copyright 2020 Google LLC (BSD-3-Clause) */
+/** Bundled JS generated from "@astrojs/lit/client-shim.js" */
+var N = Object.defineProperty;
+var i = (t, n) => () => (t && (n = t((t = 0))), n);
+var b = (t, n) => {
+	for (var a in n) N(t, a, { get: n[a], enumerable: !0 });
+};
+function s() {
+	if (d === void 0) {
+		let t = document.createElement('div');
+		(t.innerHTML = '<div><template shadowroot="open"></template></div>'), (d = !!t.firstElementChild.shadowRoot);
+	}
+	return d;
+}
+var d,
+	m = i(() => {});
+var p,
+	c,
+	f,
+	u = i(() => {
+		(p = (t) => t.parentElement === null), (c = (t) => t.tagName === 'TEMPLATE'), (f = (t) => t.nodeType === Node.ELEMENT_NODE);
+	});
+var h,
+	E = i(() => {
+		m();
+		u();
+		h = (t) => {
+			var n;
+			if (s()) return;
+			let a = [],
+				e = t.firstElementChild;
+			for (; e !== t && e !== null; )
+				if (c(e)) a.push(e), (e = e.content);
+				else if (e.firstElementChild !== null) e = e.firstElementChild;
+				else if (f(e) && e.nextElementSibling !== null) e = e.nextElementSibling;
+				else {
+					let o;
+					for (; e !== t && e !== null; )
+						if (p(e)) {
+							o = a.pop();
+							let r = o.parentElement,
+								l = o.getAttribute('shadowroot');
+							if (((e = o), l === 'open' || l === 'closed')) {
+								let y = o.hasAttribute('shadowrootdelegatesfocus');
+								try {
+									r.attachShadow({ mode: l, delegatesFocus: y }).append(o.content);
+								} catch {}
+							} else o = void 0;
+						} else {
+							let r = e.nextElementSibling;
+							if (r != null) {
+								(e = r), o !== void 0 && o.parentElement.removeChild(o);
+								break;
+							}
+							let l = (n = e.parentElement) === null || n === void 0 ? void 0 : n.nextElementSibling;
+							if (l != null) {
+								(e = l), o !== void 0 && o.parentElement.removeChild(o);
+								break;
+							}
+							(e = e.parentElement), o !== void 0 && (o.parentElement.removeChild(o), (o = void 0));
+						}
+				}
+		};
+	});
+var w = i(() => {
+	E();
+});
+var v = {};
+b(v, { hasNativeDeclarativeShadowRoots: () => s, hydrateShadowRoots: () => h });
+var S = i(() => {
+	m();
+	w();
+});
+async function g() {
+	let { hydrateShadowRoots: t } = await Promise.resolve().then(() => (S(), v));
+	t(document.body);
+}
+var x = new DOMParser().parseFromString('<p><template shadowroot="open"></template></p>', 'text/html', { includeShadowRoots: !0 }).querySelector('p');
+(!x || !x.shadowRoot) && g();
diff --git a/packages/integrations/lit/hydration-support.js b/packages/integrations/lit/hydration-support.js
new file mode 100644
index 000000000..0c21646fb
--- /dev/null
+++ b/packages/integrations/lit/hydration-support.js
@@ -0,0 +1 @@
+import 'lit/experimental-hydrate-support.js';
diff --git a/packages/integrations/lit/package.json b/packages/integrations/lit/package.json
new file mode 100644
index 000000000..2e76308f1
--- /dev/null
+++ b/packages/integrations/lit/package.json
@@ -0,0 +1,38 @@
+{
+  "name": "@astrojs/lit",
+  "version": "0.0.1",
+  "description": "Use Lit components within Astro",
+  "type": "module",
+  "types": "./dist/index.d.ts",
+  "author": "withastro",
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/withastro/astro.git",
+    "directory": "packages/integrations/lit"
+  },
+  "bugs": "https://github.com/withastro/astro/issues",
+  "homepage": "https://astro.build",
+  "exports": {
+    ".": "./dist/index.js",
+    "./server.js": "./server.js",
+    "./client-shim.js": "./client-shim.js",
+    "./hydration-support.js": "./hydration-support.js",
+    "./package.json": "./package.json"
+  },
+  "scripts": {
+    "build": "astro-scripts build \"src/**/*.ts\" && tsc",
+    "dev": "astro-scripts dev \"src/**/*.ts\""
+  },
+  "dependencies": {
+    "@lit-labs/ssr": "^2.0.2"
+  },
+  "devDependencies": {
+    "astro": "workspace:*",
+    "astro-scripts": "workspace:*"
+  },
+  "peerDependencies": {
+    "@webcomponents/template-shadowroot": "^0.1.0",
+    "lit": "^2.1.3"
+  }
+}
diff --git a/packages/integrations/lit/server-shim.js b/packages/integrations/lit/server-shim.js
new file mode 100644
index 000000000..054679592
--- /dev/null
+++ b/packages/integrations/lit/server-shim.js
@@ -0,0 +1,5 @@
+import { installWindowOnGlobal } from '@lit-labs/ssr/lib/dom-shim.js';
+installWindowOnGlobal();
+
+window.global = window;
+document.getElementsByTagName = () => [];
diff --git a/packages/integrations/lit/server.js b/packages/integrations/lit/server.js
new file mode 100644
index 000000000..1622ef619
--- /dev/null
+++ b/packages/integrations/lit/server.js
@@ -0,0 +1,72 @@
+import './server-shim.js';
+import '@lit-labs/ssr/lib/render-lit-html.js';
+import { LitElementRenderer } from '@lit-labs/ssr/lib/lit-element-renderer.js';
+
+function isCustomElementTag(name) {
+	return typeof name === 'string' && /-/.test(name);
+}
+
+function getCustomElementConstructor(name) {
+	if (typeof customElements !== 'undefined' && isCustomElementTag(name)) {
+		return customElements.get(name) || null;
+	}
+	return null;
+}
+
+async function isLitElement(Component) {
+	const Ctr = getCustomElementConstructor(Component);
+	return !!(Ctr && Ctr._$litElement$);
+}
+
+async function check(Component, _props, _children) {
+	// Lit doesn't support getting a tagName from a Constructor at this time.
+	// So this must be a string at the moment.
+	return !!(await isLitElement(Component));
+}
+
+function* render(tagName, attrs, children) {
+	const instance = new LitElementRenderer(tagName);
+
+	// LitElementRenderer creates a new element instance, so copy over.
+	const Ctr = getCustomElementConstructor(tagName);
+	for (let [name, value] of Object.entries(attrs)) {
+		// check if this is a reactive property
+		if (name in Ctr.prototype) {
+			instance.setProperty(name, value);
+		} else {
+			instance.setAttribute(name, value);
+		}
+	}
+
+	instance.connectedCallback();
+
+	yield `<${tagName}`;
+	yield* instance.renderAttributes();
+	yield `>`;
+	const shadowContents = instance.renderShadow({});
+	if (shadowContents !== undefined) {
+		yield '<template shadowroot="open">';
+		yield* shadowContents;
+		yield '</template>';
+	}
+	yield children || ''; // don’t print “undefined” as string
+	yield `</${tagName}>`;
+}
+
+async function renderToStaticMarkup(Component, props, children) {
+	let tagName = Component;
+
+	let out = '';
+	for (let chunk of render(tagName, props, children)) {
+		out += chunk;
+	}
+
+	return {
+		html: out,
+	};
+}
+
+export default {
+	check,
+	renderToStaticMarkup,
+};
diff --git a/packages/integrations/lit/src/index.ts b/packages/integrations/lit/src/index.ts
new file mode 100644
index 000000000..bf256eb84
--- /dev/null
+++ b/packages/integrations/lit/src/index.ts
@@ -0,0 +1,42 @@
+import { readFileSync } from 'node:fs';
+import type { AstroIntegration } from 'astro';
+
+function getViteConfiguration() {
+	return {
+		optimizeDeps: {
+			include: [
+				'@astrojs/lit/client-shim.js',
+				'@astrojs/lit/hydration-support.js',
+				'@webcomponents/template-shadowroot/template-shadowroot.js',
+				'lit/experimental-hydrate-support.js',
+			],
+			exclude: ['@astrojs/lit/server.js'],
+		},
+		ssr: {
+			external: ['lit-element/lit-element.js', '@lit-labs/ssr/lib/install-global-dom-shim.js', '@lit-labs/ssr/lib/render-lit-html.js', '@lit-labs/ssr/lib/lit-element-renderer.js'],
+		},
+	};
+}
+
+export default function (): AstroIntegration {
+	return {
+		name: '@astrojs/lit',
+		hooks: {
+			'astro:config:setup': ({ updateConfig, addRenderer, injectScript }) => {
+				// Inject the necessary polyfills on every page (inlined for speed).
+				injectScript('head-inline', readFileSync(new URL('../client-shim.min.js', import.meta.url), { encoding: 'utf-8' }));
+				// Inject the hydration code, before a component is hydrated.
+				injectScript('before-hydration', `import '@astrojs/lit/hydration-support.js';`);
+				// Add the lit renderer so that Astro can understand lit components.
+				addRenderer({
+					name: '@astrojs/lit',
+					serverEntrypoint: '@astrojs/lit/server.js',
+				});
+				// Update the vite configuration.
+				updateConfig({
+					vite: getViteConfiguration(),
+				});
+			},
+		},
+	};
+}
diff --git a/packages/integrations/lit/tsconfig.json b/packages/integrations/lit/tsconfig.json
new file mode 100644
index 000000000..44baf375c
--- /dev/null
+++ b/packages/integrations/lit/tsconfig.json
@@ -0,0 +1,10 @@
+{
+  "extends": "../../../tsconfig.base.json",
+  "include": ["src"],
+  "compilerOptions": {
+    "allowJs": true,
+    "module": "ES2020",
+    "outDir": "./dist",
+    "target": "ES2020"
+  }
+}