Refactor Svelte preprocess integration handling (#5901)

* Let user setup vitePreprocess

* Abstract function

* Add changeset

* Update svelte syntax

* Make fallback

* Fix docs

* Update changeset

* Fix types

.changeset/chatty-planes-bathe.md

@@ -0,0 +1,18 @@
+---
+'@astrojs/svelte': major
+'astro': minor
+---
+
+The fallback Svelte preprocessor will only be applied if a custom `preprocess` option is not passed to the `svelte()` integration option, or in the `svelte.config.js` file.
+
+To support IDE autocompletion, or if you're migrating from `@astrojs/svelte` v1, you can create a `svelte.config.js` file with:
+
+```js
+import { vitePreprocess } from '@astrojs/svelte';
+
+export default {
+	preprocess: vitePreprocess(),
+};
+```
+
+This file will also be generated by `astro add svelte` by default.

examples/framework-svelte/svelte.config.js

@@ -0,0 +1,5 @@
+import { vitePreprocess } from '@astrojs/svelte';
+
+export default {
+	preprocess: vitePreprocess(),
+};

packages/astro/src/core/add/index.ts

@@ -53,6 +53,13 @@ module.exports = {
 	},
 	plugins: [],
 }\n`;
+const SVELTE_CONFIG_STUB = `\
+import { vitePreprocess } from '@astrojs/svelte';
+
+export default {
+	preprocess: vitePreprocess(),
+};
+`;
 
 const OFFICIAL_ADAPTER_TO_IMPORT_MAP: Record<string, string> = {
 	netlify: '@astrojs/netlify/functions',
@@ -114,37 +121,30 @@ export default async function add(names: string[], { cwd, flags, logging, teleme
 	switch (installResult) {
 		case UpdateResult.updated: {
 			if (integrations.find((integration) => integration.id === 'tailwind')) {
-				const possibleConfigFiles = [
-					'./tailwind.config.cjs',
-					'./tailwind.config.mjs',
-					'./tailwind.config.js',
-				].map((p) => fileURLToPath(new URL(p, root)));
-				let alreadyConfigured = false;
-				for (const possibleConfigPath of possibleConfigFiles) {
-					if (existsSync(possibleConfigPath)) {
-						alreadyConfigured = true;
-						break;
-					}
-				}
-				if (!alreadyConfigured) {
-					info(
-						logging,
-						null,
-						`\n  ${magenta(
-							`Astro will generate a minimal ${bold('./tailwind.config.cjs')} file.`
-						)}\n`
-					);
-					if (await askToContinue({ flags })) {
-						await fs.writeFile(
-							fileURLToPath(new URL('./tailwind.config.cjs', root)),
-							TAILWIND_CONFIG_STUB,
-							{ encoding: 'utf-8' }
-						);
-						debug('add', `Generated default ./tailwind.config.cjs file`);
-					}
-				} else {
-					debug('add', `Using existing Tailwind configuration`);
-				}
+				await setupIntegrationConfig({
+					root,
+					logging,
+					flags,
+					integrationName: 'Tailwind',
+					possibleConfigFiles: [
+						'./tailwind.config.cjs',
+						'./tailwind.config.mjs',
+						'./tailwind.config.js',
+					],
+					defaultConfigFile: './tailwind.config.cjs',
+					defaultConfigContent: TAILWIND_CONFIG_STUB,
+				});
+			}
+			if (integrations.find((integration) => integration.id === 'svelte')) {
+				await setupIntegrationConfig({
+					root,
+					logging,
+					flags,
+					integrationName: 'Svelte',
+					possibleConfigFiles: ['./svelte.config.js', './svelte.config.cjs', './svelte.config.mjs'],
+					defaultConfigFile: './svelte.config.js',
+					defaultConfigContent: SVELTE_CONFIG_STUB,
+				});
 			}
 			break;
 		}
@@ -886,3 +886,43 @@ function getDiffContent(input: string, output: string): string | null {
 
 	return diffed;
 }
+
+async function setupIntegrationConfig(opts: {
+	root: URL;
+	logging: LogOptions;
+	flags: yargs.Arguments;
+	integrationName: string;
+	possibleConfigFiles: string[];
+	defaultConfigFile: string;
+	defaultConfigContent: string;
+}) {
+	const possibleConfigFiles = opts.possibleConfigFiles.map((p) =>
+		fileURLToPath(new URL(p, opts.root))
+	);
+	let alreadyConfigured = false;
+	for (const possibleConfigPath of possibleConfigFiles) {
+		if (existsSync(possibleConfigPath)) {
+			alreadyConfigured = true;
+			break;
+		}
+	}
+	if (!alreadyConfigured) {
+		info(
+			opts.logging,
+			null,
+			`\n  ${magenta(`Astro will generate a minimal ${bold(opts.defaultConfigFile)} file.`)}\n`
+		);
+		if (await askToContinue({ flags: opts.flags })) {
+			await fs.writeFile(
+				fileURLToPath(new URL(opts.defaultConfigFile, opts.root)),
+				opts.defaultConfigContent,
+				{
+					encoding: 'utf-8',
+				}
+			);
+			debug('add', `Generated default ${opts.defaultConfigFile} file`);
+		}
+	} else {
+		debug('add', `Using existing ${opts.integrationName} configuration`);
+	}
+}

packages/integrations/svelte/README.md

@@ -84,18 +84,44 @@ A few of the default options passed to the Svelte compiler are required to build
 const defaultOptions = {
   emitCss: true,
   compilerOptions: { dev: isDev, hydratable: true },
-  preprocess: [
-    preprocess({
-      less: true,
-      sass: { renderSync: true },
-      scss: { renderSync: true },
-      stylus: true,
-      typescript: true,
-    }),
-  ],
+  preprocess: vitePreprocess()
 };
 ```
 
 The `emitCss`, `compilerOptions.dev`, and `compilerOptions.hydratable` cannot be overridden.
 
-Providing your own `preprocess` options **will** override the defaults - make sure to enable the preprocessor flags needed for your project.
+Providing your own `preprocess` options **will** override the defaults - make sure to enable the preprocessor flags needed for your project. For example,
+
+```js
+// astro.config.js
+import svelte from '@astrojs/svelte';
+
+export default {
+  integrations: [svelte({ preprocess: [] })],
+};
+```
+
+and
+
+```js
+// svelte.config.js
+export default {
+  preprocess: [],
+};
+```
+
+Will override the default `preprocess` option. You can read the [`vitePreprocess` docs](https://github.com/sveltejs/vite-plugin-svelte/blob/HEAD/docs/preprocess.md) for more information of how it works.
+
+## Intellisense for TypeScript
+
+If you're using a preprocessor like TypeScript or SCSS in your Svelte files, you can create a `svelte.config.js` file with:
+
+```js
+import { vitePreprocess } from '@astrojs/svelte';
+
+export default {
+	preprocess: vitePreprocess(),
+};
+```
+
+So the Svelte IDE extension can correctly parse the Svelte files. This config file is added by default when you run `astro add svelte`.

packages/integrations/svelte/src/index.ts

@@ -2,6 +2,7 @@ import type { Options } from '@sveltejs/vite-plugin-svelte';
 import { svelte, vitePreprocess } from '@sveltejs/vite-plugin-svelte';
 import type { AstroIntegration, AstroRenderer } from 'astro';
 import type { UserConfig } from 'vite';
+import { fileURLToPath } from 'url';
 
 function getRenderer(): AstroRenderer {
 	return {
@@ -11,16 +12,27 @@ function getRenderer(): AstroRenderer {
 	};
 }
 
+async function svelteConfigHasPreprocess(root: URL) {
+	const svelteConfigFiles = ['./svelte.config.js', './svelte.config.cjs', './svelte.config.mjs'];
+	for (const file of svelteConfigFiles) {
+		const filePath = fileURLToPath(new URL(file, root));
+		try {
+			const config = (await import(filePath)).default;
+			return !!config.preprocess;
+		} catch {}
+	}
+}
+
 type ViteConfigurationArgs = {
 	isDev: boolean;
 	options?: Options | OptionsCallback;
+	root: URL;
 };
 
-function getViteConfiguration({ options, isDev }: ViteConfigurationArgs): UserConfig {
+async function getViteConfiguration({ options, isDev, root }: ViteConfigurationArgs): Promise<UserConfig> {
 	const defaultOptions: Partial<Options> = {
 		emitCss: true,
 		compilerOptions: { dev: isDev, hydratable: true },
-		preprocess: [vitePreprocess()],
 	};
 
 	// Disable hot mode during the build
@@ -43,11 +55,13 @@ function getViteConfiguration({ options, isDev }: ViteConfigurationArgs): UserCo
 				// Always use dev and hydratable from defaults
 				...defaultOptions.compilerOptions,
 			},
-			// Ignore default preprocessor if the user provided their own
-			preprocess: options.preprocess ?? defaultOptions.preprocess,
 		};
 	}
 
+	if (!resolvedOptions.preprocess && !(await svelteConfigHasPreprocess(root))) {
+		resolvedOptions.preprocess = vitePreprocess();
+	}
+
 	return {
 		optimizeDeps: {
 			include: ['@astrojs/svelte/client.js'],
@@ -63,15 +77,18 @@ export default function (options?: Options | OptionsCallback): AstroIntegration
 		name: '@astrojs/svelte',
 		hooks: {
 			// Anything that gets returned here is merged into Astro Config
-			'astro:config:setup': ({ command, updateConfig, addRenderer }) => {
+			'astro:config:setup': async ({ command, updateConfig, addRenderer, config }) => {
 				addRenderer(getRenderer());
 				updateConfig({
-					vite: getViteConfiguration({
+					vite: await getViteConfiguration({
 						options,
 						isDev: command === 'dev',
+						root: config.root,
 					}),
 				});
 			},
 		},
 	};
 }
+
+export { vitePreprocess };