fix: avoid running init hook during builds when there's nothing to prerender (#14464)

fixes #14347

This PR reverts the fix from #14219 which caused the init hook to run even if there's nothing to prerender. Instead of running the init hook early, we just set the env variables when looking for prerendered remote functions. This avoids any errors for missing env variables when evaluating the user's remote function modules. We only run the init hook once we've found things we need to prerender.

Author: teemingc

.changeset/loose-parks-exist.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: avoid running the `init` hook during builds if there's nothing to prerender

packages/kit/src/core/postbuild/prerender.js

@@ -15,6 +15,7 @@ import * as devalue from 'devalue';
 import { createReadableStream } from '@sveltejs/kit/node';
 import generate_fallback from './fallback.js';
 import { stringify_remote_arg } from '../../runtime/shared.js';
+import { filter_env } from '../../utils/env.js';
 
 export default forked(import.meta.url, prerender);
 
@@ -125,12 +126,6 @@ async function prerender({ hash, out, manifest_path, metadata, verbose, env }) {
 
 	installPolyfills();
 
-	const server = new Server(manifest);
-	await server.init({
-		env,
-		read: (file) => createReadableStream(`${config.outDir}/output/server/${file}`)
-	});
-
 	/** @type {Map<string, string>} */
 	const saved = new Map();
 
@@ -489,6 +484,15 @@ async function prerender({ hash, out, manifest_path, metadata, verbose, env }) {
 		}
 	}
 
+	// the user's remote function modules may reference environment variables at
+	// the top-level so we need to set `env` before evaluating those modules
+	// to avoid potential runtime errors
+	const { publicPrefix: public_prefix, privatePrefix: private_prefix } = config.env;
+	const private_env = filter_env(env, private_prefix, public_prefix);
+	const public_env = filter_env(env, public_prefix, private_prefix);
+	internal.set_private_env(private_env);
+	internal.set_public_env(public_env);
+
 	/** @type {Array<import('types').RemoteInfo & { type: 'prerender'}>} */
 	const prerender_functions = [];
 
@@ -507,6 +511,14 @@ async function prerender({ hash, out, manifest_path, metadata, verbose, env }) {
 		return { prerendered, prerender_map };
 	}
 
+	// only run the server after the `should_prerender` check so that we
+	// don't run the user's init hook unnecessarily
+	const server = new Server(manifest);
+	await server.init({
+		env,
+		read: (file) => createReadableStream(`${config.outDir}/output/server/${file}`)
+	});
+
 	log.info('Prerendering');
 
 	for (const entry of config.prerender.entries) {

packages/kit/test/apps/options/source/hooks.server.js

@@ -1,3 +1,4 @@
+import { building } from '$app/environment';
 import { env } from '$env/dynamic/private';
 
 // this verifies that dynamic env vars can be read during analysis phase
@@ -13,3 +14,11 @@ export function handle({ event, resolve }) {
 		preload: ({ type }) => type !== 'css'
 	});
 }
+
+export function init() {
+	if (building) {
+		throw new Error(
+			'There are no prerendered pages or functions in this app so init() should not be called during the build'
+		);
+	}
+}