Statically analyse exports v2

packages/kit/package.json

@@ -18,7 +18,9 @@
 	"homepage": "https://svelte.dev",
 	"type": "module",
 	"dependencies": {
+		"@sveltejs/acorn-typescript": "^1.0.5",
 		"@types/cookie": "^0.6.0",
+		"acorn": "^8.14.1",
 		"cookie": "^0.6.0",
 		"devalue": "^5.1.0",
 		"esm-env": "^1.2.2",

packages/kit/src/exports/vite/build/build_server.js

@@ -101,12 +101,17 @@ export function build_server_nodes(out, kit, manifest_data, server_manifest, cli
 		}
 
 		if (node.universal) {
-			imports.push(
-				`import * as universal from '../${
-					resolve_symlinks(server_manifest, node.universal).chunk.file
-				}';`
-			);
-			exports.push('export { universal };');
+			if (node.universal_static_exports?.ssr === false) {
+				const universal_exports = Object.entries(node.universal_static_exports).map(([name, value]) => `${name}: ${s(value)}`);
+				exports.push(`export const universal = { ${universal_exports} };`);
+			} else {
+				imports.push(
+					`import * as universal from '../${
+						resolve_symlinks(server_manifest, node.universal).chunk.file
+					}';`
+				);
+				exports.push('export { universal };');
+			}
 			exports.push(`export const universal_id = ${s(node.universal)};`);
 		}
 

packages/kit/src/exports/vite/dev/index.js

@@ -202,6 +202,7 @@ export async function dev(vite, vite_config, svelte_config) {
 						}
 
 						if (node.universal) {
+							// TODO: avoid loading the module if ssr is false
 							const { module, module_node } = await resolve(node.universal);
 							module_nodes.push(module_node);
 							result.universal = module;

packages/kit/src/exports/vite/index.js

@@ -17,7 +17,13 @@ import { assets_base, find_deps, resolve_symlinks } from './build/utils.js';
 import { dev } from './dev/index.js';
 import { is_illegal, module_guard } from './graph_analysis/index.js';
 import { preview } from './preview/index.js';
-import { get_config_aliases, get_env, normalize_id, strip_virtual_prefix } from './utils.js';
+import {
+	get_config_aliases,
+	get_env,
+	normalize_id,
+	statically_analyse_exports,
+	strip_virtual_prefix
+} from './utils.js';
 import { write_client_manifest } from '../../core/sync/write_client_manifest.js';
 import prerender from '../../core/postbuild/prerender.js';
 import analyse from '../../core/postbuild/analyse.js';
@@ -731,6 +737,19 @@ Tips:
 			return preview(vite, vite_config, svelte_config);
 		},
 
+		transform(code, id) {
+			const route_path = id.slice(process.cwd().length + 1);
+			const node = manifest_data.nodes.find(
+				(node) => node.universal && node.universal === route_path
+			);
+			if (!node) return;
+
+			const exports = statically_analyse_exports(this.parse(code));
+			if (exports) {
+				node.universal_static_exports = Object.fromEntries(exports);
+			}
+		},
+
 		/**
 		 * Clears the output directories.
 		 */

packages/kit/src/exports/vite/utils.js

@@ -1,6 +1,6 @@
 import path from 'node:path';
 import { loadEnv } from 'vite';
-import { posixify } from '../../utils/filesystem.js';
+import { posixify, read } from '../../utils/filesystem.js';
 import { negotiate } from '../../utils/http.js';
 import { filter_private_env, filter_public_env } from '../../utils/env.js';
 import { escape_html } from '../../utils/escape.js';
@@ -156,3 +156,52 @@
 }
 
 export const strip_virtual_prefix = /** @param {string} id */ (id) => id.replace('\0virtual:', '');
+
+/**
+ * Collect all public exports (i.e. not starting with `_`) from a +page.js/+layout.js file.
+ * Returns `null` if those exports cannot be statically analyzed.
+ * @param {import('rollup').ProgramNode} ast
+ */
+export function statically_analyse_exports(ast) {
+	/** @type {Map<string, any>} */
+	const exports = new Map();
+
+	for (const statement of ast.body) {
+		if (statement.type === 'ExportAllDeclaration') return null;
+		if (statement.type !== 'ExportNamedDeclaration') continue;
+		// TODO: handle export specifiers referencing identifiers in the same file?
+		if (statement.specifiers.length > 0) return null;
+
+		if (statement.declaration?.type === 'FunctionDeclaration') {
+			if (statement.declaration.id.name.startsWith('_')) continue;
+			// We need to load the file during prerendering
+			if (statement.declaration.id.name === 'entries') return null;
+			// This includes load functions but also other invalid public function exports which our validator will catch
+			// TODO should instead just bail on everything invalid, to indirectly trigger validation? or error directly here?
+			exports.set(statement.declaration.id.name, 'function');
+			continue;
+		}
+
+		if (
+			statement.declaration?.type !== 'VariableDeclaration' ||
+			statement.declaration.kind !== 'const'
+		) {
+			// TODO analyze that variable is not reassigned, i.e. so that `let` is also allowed?
+			return null;
+		}
+
+		for (const declaration of statement.declaration.declarations) {
+			if (declaration.id.type !== 'Identifier') return null;
+			if (declaration.id.name.startsWith('_') || declaration.id.name === 'load') continue;
+
+			if (!declaration.init || declaration.init.type !== 'Literal') {
+				// TODO try to statically analyze ObjectExpression in case of `export const config = { ... }`
+				return null;
+			}
+
+			exports.set(declaration.id.name, declaration.init.value);
+		}
+	}
+
+	return exports;
+}

packages/kit/src/runtime/server/respond.js

@@ -288,7 +288,7 @@ export async function respond(request, options, manifest, state) {
 	let trailing_slash = 'never';
 
 	try {
-		/** @type {PageNodes|undefined} */
+		/** @type {PageNodes | undefined} */
 		const page_nodes = route?.page
 			? new PageNodes(await load_page_nodes(route.page, manifest))
 			: undefined;

packages/kit/src/types/internal.d.ts

@@ -199,6 +199,8 @@ export interface PageNode {
 	component?: string; // TODO supply default component if it's missing (bit of an edge case)
 	/** The `+page/layout.js/.ts`. */
 	universal?: string;
+	/** The `+page/layout.js/.ts` exports we could analyze statically, and their values */
+	universal_static_exports?: Omit<UniversalNode, 'load' | 'entries'> & Record<string, any>;
 	/** The `+page/layout.server.js/ts`. */
 	server?: string;
 	parent_id?: string;
@@ -409,6 +411,12 @@ export interface SSRNode {
 	universal?: UniversalNode;
 	/** +page.server.js, +layout.server.js, or +server.js */
 	server?: ServerNode;
+	statically_analysed_option?: {
+		ssr?: boolean;
+		csr?: boolean;
+		prerender?: boolean;
+		trailingSlash?: TrailingSlash;
+	};
 }
 
 export type SSRNodeLoader = () => Promise<SSRNode>;

packages/kit/src/utils/page_nodes.js

@@ -27,13 +27,15 @@ export class PageNodes {
 		for (const layout of this.layouts()) {
 			if (layout) {
 				validate_layout_server_exports(layout.server, /** @type {string} */ (layout.server_id));
+				// TODO: validate exports without loading the module?
 				validate_layout_exports(layout.universal, /** @type {string} */ (layout.universal_id));
 			}
 		}
 
 		const page = this.page();
 		if (page) {
 			validate_page_server_exports(page.server, /** @type {string} */ (page.server_id));
+			// TODO: validate exports without loading the module?
 			validate_page_exports(page.universal, /** @type {string} */ (page.universal_id));
 		}
 	}