Allow SSR dynamic routes to not implement getStaticPaths (#2815)

* Allow SSR dynamic routes to not implement getStaticPaths

* Adds a changeset

* Update based on code-review comments

12 files changed, 81 insertions, 25 deletions

diff --git a/.changeset/spotty-houses-stare.md b/.changeset/spotty-houses-stare.md
new file mode 100644
index 000000000..a3672caf8
--- /dev/null
+++ b/.changeset/spotty-houses-stare.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Allows dynamic routes in SSR to avoid implementing getStaticPaths
diff --git a/examples/ssr/astro.config.mjs b/examples/ssr/astro.config.mjs
index fd25be136..c8e5061a6 100644
--- a/examples/ssr/astro.config.mjs
+++ b/examples/ssr/astro.config.mjs
@@ -1,4 +1,4 @@
-// @ts-check
+import { defineConfig } from 'astro/config';
 
 export default defineConfig({
 	renderers: ['@astrojs/renderer-svelte'],
diff --git a/examples/ssr/src/pages/products/[id].astro b/examples/ssr/src/pages/products/[id].astro
index 9c400c2f1..37fe7e0b4 100644
--- a/examples/ssr/src/pages/products/[id].astro
+++ b/examples/ssr/src/pages/products/[id].astro
@@ -2,18 +2,9 @@
 import Header from '../../components/Header.astro';
 import Container from '../../components/Container.astro';
 import AddToCart from '../../components/AddToCart.svelte';
-import { getProducts, getProduct } from '../../api';
+import { getProduct } from '../../api';
 import '../../styles/common.css';
 
-export async function getStaticPaths() {
-	const products = await getProducts();
-	return products.map(product => {
-		return {
-			params: { id: product.id.toString() }
-		}
-	});
-}
-
 const id = Number(Astro.request.params.id);
 const product = await getProduct(id);
 ---
diff --git a/packages/astro/src/core/build/index.ts b/packages/astro/src/core/build/index.ts
index ece445aa0..db06851d2 100644
--- a/packages/astro/src/core/build/index.ts
+++ b/packages/astro/src/core/build/index.ts
@@ -83,6 +83,7 @@ class AstroBuilder {
 			origin,
 			routeCache: this.routeCache,
 			viteServer: this.viteServer,
+			ssr: this.config.buildOptions.experimentalSsr,
 		});
 
 		// Filter pages by using conditions based on their frontmatter.
diff --git a/packages/astro/src/core/build/page-data.ts b/packages/astro/src/core/build/page-data.ts
index 53c1b15d0..4cf96d388 100644
--- a/packages/astro/src/core/build/page-data.ts
+++ b/packages/astro/src/core/build/page-data.ts
@@ -17,6 +17,7 @@ export interface CollectPagesDataOptions {
 	origin: string;
 	routeCache: RouteCache;
 	viteServer: ViteDevServer;
+	ssr: boolean;
 }
 
 export interface CollectPagesDataResult {
@@ -109,11 +110,11 @@ export async function collectPagesData(opts: CollectPagesDataOptions): Promise<C
 }
 
 async function getStaticPathsForRoute(opts: CollectPagesDataOptions, route: RouteData): Promise<RouteCacheEntry> {
-	const { astroConfig, logging, routeCache, viteServer } = opts;
+	const { astroConfig, logging, routeCache, ssr, viteServer } = opts;
 	if (!viteServer) throw new Error(`vite.createServer() not called!`);
 	const filePath = new URL(`./${route.component}`, astroConfig.projectRoot);
 	const mod = (await viteServer.ssrLoadModule(fileURLToPath(filePath))) as ComponentInstance;
-	const result = await callGetStaticPaths(mod, route, false, logging);
+	const result = await callGetStaticPaths({ mod, route, isValidate: false, logging, ssr });
 	routeCache.set(route, result);
 	return result;
 }
diff --git a/packages/astro/src/core/render/core.ts b/packages/astro/src/core/render/core.ts
index 7d969240c..f5c05d0a5 100644
--- a/packages/astro/src/core/render/core.ts
+++ b/packages/astro/src/core/render/core.ts
@@ -13,6 +13,7 @@ interface GetParamsAndPropsOptions {
 	routeCache: RouteCache;
 	pathname: string;
 	logging: LogOptions;
+	ssr: boolean;
 }
 
 export const enum GetParamsAndPropsError {
@@ -20,7 +21,7 @@ export const enum GetParamsAndPropsError {
 }
 
 export async function getParamsAndProps(opts: GetParamsAndPropsOptions): Promise<[Params, Props] | GetParamsAndPropsError> {
-	const { logging, mod, route, routeCache, pathname } = opts;
+	const { logging, mod, route, routeCache, pathname, ssr} = opts;
 	// Handle dynamic routes
 	let params: Params = {};
 	let pageProps: Props;
@@ -37,18 +38,18 @@ export async function getParamsAndProps(opts: GetParamsAndPropsOptions): Promise
 		// TODO(fks): Can we refactor getParamsAndProps() to receive routeCacheEntry
 		// as a prop, and not do a live lookup/populate inside this lower function call.
 		if (!routeCacheEntry) {
-			routeCacheEntry = await callGetStaticPaths(mod, route, true, logging);
+			routeCacheEntry = await callGetStaticPaths({ mod, route, isValidate: true, logging, ssr });
 			routeCache.set(route, routeCacheEntry);
 		}
 		const matchedStaticPath = findPathItemByKey(routeCacheEntry.staticPaths, params);
-		if (!matchedStaticPath) {
+		if (!matchedStaticPath && !ssr) {
 			return GetParamsAndPropsError.NoMatchingStaticPath;
 		}
 		// Note: considered using Object.create(...) for performance
 		// Since this doesn't inherit an object's properties, this caused some odd user-facing behavior.
 		// Ex. console.log(Astro.props) -> {}, but console.log(Astro.props.property) -> 'expected value'
 		// Replaced with a simple spread as a compromise
-		pageProps = matchedStaticPath.props ? { ...matchedStaticPath.props } : {};
+		pageProps = matchedStaticPath?.props ? { ...matchedStaticPath.props } : {};
 	} else {
 		pageProps = {};
 	}
@@ -83,6 +84,7 @@ export async function render(opts: RenderOptions): Promise<{ type: 'html'; html:
 		route,
 		routeCache,
 		pathname,
+		ssr,
 	});
 
 	if (paramsAndPropsRes === GetParamsAndPropsError.NoMatchingStaticPath) {
diff --git a/packages/astro/src/core/render/route-cache.ts b/packages/astro/src/core/render/route-cache.ts
index 43f41717e..5ae36fcb0 100644
--- a/packages/astro/src/core/render/route-cache.ts
+++ b/packages/astro/src/core/render/route-cache.ts
@@ -11,19 +11,29 @@ function stringifyParams(params: Params) {
 	return JSON.stringify(params, Object.keys(params).sort());
 }
 
-export async function callGetStaticPaths(mod: ComponentInstance, route: RouteData, isValidate: boolean, logging: LogOptions): Promise<RouteCacheEntry> {
-	validateGetStaticPathsModule(mod);
+interface CallGetStaticPathsOptions {
+	mod: ComponentInstance;
+	route: RouteData;
+	isValidate: boolean;
+	logging: LogOptions;
+	ssr: boolean;
+}
+
+export async function callGetStaticPaths({ isValidate, logging, mod, route, ssr}: CallGetStaticPathsOptions): Promise<RouteCacheEntry> {
+	validateGetStaticPathsModule(mod, { ssr });
 	const resultInProgress = {
 		rss: [] as RSS[],
 	};
-	const staticPaths: GetStaticPathsResult = await (
-		await mod.getStaticPaths!({
+
+	let staticPaths: GetStaticPathsResult = [];
+	if(mod.getStaticPaths) {
+		staticPaths = (await mod.getStaticPaths({
 			paginate: generatePaginateFunction(route),
 			rss: (data) => {
 				resultInProgress.rss.push(data);
 			},
-		})
-	).flat();
+		})).flat();
+	}
 
 	const keyedStaticPaths = staticPaths as GetStaticPathsResultKeyed;
 	keyedStaticPaths.keyed = new Map<string, GetStaticPathsItem>();
diff --git a/packages/astro/src/core/routing/validation.ts b/packages/astro/src/core/routing/validation.ts
index d1d19e98f..d8fda32c4 100644
--- a/packages/astro/src/core/routing/validation.ts
+++ b/packages/astro/src/core/routing/validation.ts
@@ -2,12 +2,16 @@ import type { ComponentInstance, GetStaticPathsResult } from '../../@types/astro
 import type { LogOptions } from '../logger';
 import { warn } from '../logger.js';
 
+interface ValidationOptions {
+	ssr: boolean;
+}
+
 /** Throw error for deprecated/malformed APIs */
-export function validateGetStaticPathsModule(mod: ComponentInstance) {
+export function validateGetStaticPathsModule(mod: ComponentInstance, { ssr }: ValidationOptions) {
 	if ((mod as any).createCollection) {
 		throw new Error(`[createCollection] deprecated. Please use getStaticPaths() instead.`);
 	}
-	if (!mod.getStaticPaths) {
+	if (!mod.getStaticPaths && !ssr) {
 		throw new Error(`[getStaticPaths] getStaticPaths() function is required. Make sure that you \`export\` the function from your component.`);
 	}
 }
diff --git a/packages/astro/src/vite-plugin-astro-server/index.ts b/packages/astro/src/vite-plugin-astro-server/index.ts
index 900216377..bc45596da 100644
--- a/packages/astro/src/vite-plugin-astro-server/index.ts
+++ b/packages/astro/src/vite-plugin-astro-server/index.ts
@@ -152,6 +152,7 @@ async function handleRequest(
 			routeCache,
 			pathname: rootRelativeUrl,
 			logging,
+			ssr: config.buildOptions.experimentalSsr,
 		});
 		if (paramsAndPropsRes === GetParamsAndPropsError.NoMatchingStaticPath) {
 			warn(logging, 'getStaticPaths', `Route pattern matched, but no matching static path found. (${pathname})`);
diff --git a/packages/astro/test/fixtures/ssr-dynamic/src/pages/[id].astro b/packages/astro/test/fixtures/ssr-dynamic/src/pages/[id].astro
new file mode 100644
index 000000000..b976757e2
--- /dev/null
+++ b/packages/astro/test/fixtures/ssr-dynamic/src/pages/[id].astro
@@ -0,0 +1,11 @@
+---
+const val = Number(Astro.request.params.id);
+---
+<html>
+<head>
+	<title>Test app</title>
+</head>
+<body>
+	<h1>Item { val }</h1>
+</body>
+</html>
diff --git a/packages/astro/test/ssr-dynamic.test.js b/packages/astro/test/ssr-dynamic.test.js
new file mode 100644
index 000000000..70e3b0aee
--- /dev/null
+++ b/packages/astro/test/ssr-dynamic.test.js
@@ -0,0 +1,28 @@
+import { expect } from 'chai';
+import { load as cheerioLoad } from 'cheerio';
+import { loadFixture } from './test-utils.js';
+
+// Asset bundling
+describe('Dynamic pages in SSR', () => {
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			projectRoot: './fixtures/ssr-dynamic/',
+			buildOptions: {
+				experimentalSsr: true,
+			}
+		});
+		await fixture.build();
+	});
+
+	it('Do not have to implement getStaticPaths', async () => {
+		const app = await fixture.loadSSRApp();
+		const request = new Request("http://example.com/123");
+		const route = app.match(request);
+		const response = await app.render(request, route);
+		const html = await response.text();
+		const $ = cheerioLoad(html);
+		expect($('h1').text()).to.equal('Item 123');
+	});
+});
diff --git a/packages/astro/test/test-utils.js b/packages/astro/test/test-utils.js
index c7060dcc7..494047ae3 100644
--- a/packages/astro/test/test-utils.js
+++ b/packages/astro/test/test-utils.js
@@ -6,6 +6,7 @@ import { loadConfig } from '../dist/core/config.js';
 import dev from '../dist/core/dev/index.js';
 import build from '../dist/core/build/index.js';
 import preview from '../dist/core/preview/index.js';
+import { loadApp } from '../dist/core/app/node.js';
 import os from 'os';
 import stripAnsi from 'strip-ansi';
 
@@ -86,6 +87,7 @@ export async function loadFixture(inlineConfig) {
 			inlineConfig.devOptions.port = previewServer.port; // update port for fetch
 			return previewServer;
 		},
+		loadSSRApp: () => loadApp(new URL('./server/', config.dist)),
 		readFile: (filePath) => fs.promises.readFile(new URL(filePath.replace(/^\//, ''), config.dist), 'utf8'),
 		readdir: (fp) => fs.promises.readdir(new URL(fp.replace(/^\//, ''), config.dist)),
 		clean: () => fs.promises.rm(config.dist, { maxRetries: 10, recursive: true, force: true }),