Feature: List rendered components during SSR

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

@@ -1051,12 +1051,14 @@ A server-side component exposes a `render` method that can be called with option
 
 You can import a Svelte component directly into Node using [`svelte/register`](docs#svelte_register).
 
+`renderedComponents` contains an array of filenames of components that were rendered during SSR. The filenames come from `svelte.compile({filename: '...' })`, which is generally done behind the scenes by your bundler (eg: Rollup). You can match these file names to your asset modules in order to preload asynchronous components that will be required on the client-side ahead-of-time.
+
 ```js
 require('svelte/register');
 
 const App = require('./App.svelte').default;
 
-const { head, html, css } = App.render({
+const { head, html, css, renderedComponents } = App.render({
 	answer: 42
 });
 ```

src/compiler/compile/render_ssr/index.ts

@@ -134,6 +134,7 @@ export default function ssr(
 		instance_javascript,
 		...parent_bindings,
 		css.code && b`$$result.css.add(#css);`,
+		options.filename && b`$$result.renderedComponents.add('${options.filename}');`,
 		main
 	].filter(Boolean);
 

src/runtime/internal/ssr.ts

@@ -107,7 +107,8 @@ export function create_ssr_component(fn) {
 					map: null;
 					code: string;
 				}>;
-			} = { title: '', head: '', css: new Set() };
+				renderedComponents: Set<string>;
+			} = { title: '', head: '', css: new Set(), renderedComponents: new Set() };
 
 			const html = $$render(result, props, {}, options);
 
@@ -119,7 +120,8 @@ export function create_ssr_component(fn) {
 					code: Array.from(result.css).map(css => css.code).join('\n'),
 					map: null // TODO
 				},
-				head: result.title + result.head
+				head: result.title + result.head,
+				renderedComponents: Array.from(result.renderedComponents)
 			};
 		},
 

test/server-side-rendering/index.ts

@@ -37,7 +37,6 @@ describe('ssr', () => {
 		if (dir[0] === '.') return;
 
 		const config = loadConfig(`${__dirname}/samples/${dir}/_config.js`);
-
 		// add .solo to a sample directory name to only run that test, or
 		// .show to always show the output. or both
 		const solo = config.solo || /\.solo/.test(dir);
@@ -76,7 +75,11 @@ describe('ssr', () => {
 				if (css.code) fs.writeFileSync(`${dir}/_actual.css`, css.code);
 
 				try {
-					assert.htmlEqual(html, expectedHtml);
+					if (config.testForRenderedComponents) {
+						assert.ok(rendered.renderedComponents[0].includes('main.svelte'));
+					} else {
+						assert.htmlEqual(html, expectedHtml);
+					}
 				} catch (error) {
 					if (shouldUpdateExpected()) {
 						fs.writeFileSync(`${dir}/_expected.html`, html);

test/server-side-rendering/samples/renderedComponents/_config.js

@@ -0,0 +1,3 @@
+export default {
+    testForRenderedComponents: true
+};