Use mtime as timestamp when loading config file (#356)

* Use mtime as timestamp when loading config file Co-authored-by: Conduitry <git@chor.date> * Export loadSvelteConfig Co-authored-by: Conduitry <git@chor.date>

Author: benmccann

.changeset/tidy-months-explode.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+Use last modified time as cache busting parameter

.changeset/two-rice-end.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+Export loadSvelteConfig

packages/vite-plugin-svelte/src/index.ts

@@ -218,6 +218,8 @@ export function svelte(inlineOptions?: Partial<Options>): Plugin[] {
 return plugins.filter(Boolean);
 }
 
+export { loadSvelteConfig } from './utils/load-svelte-config';
+
 export {
 Options,
 Preprocessor,

packages/vite-plugin-svelte/src/utils/load-svelte-config.ts

@@ -22,14 +22,15 @@ export const knownSvelteConfigNames = [
 // also use timestamp query to avoid caching on reload
 const dynamicImportDefault = new Function(
 'path',
-'return import(path + "?t=" + Date.now()).then(m => m.default)'
+'timestamp',
+'return import(path + "?t=" + timestamp).then(m => m.default)'
 );
 
 export async function loadSvelteConfig(
-viteConfig: UserConfig,
-inlineOptions: Partial<Options>
+viteConfig?: UserConfig,
+inlineOptions?: Partial<Options>
 ): Promise<Partial<Options> | undefined> {
-if (inlineOptions.configFile === false) {
+if (inlineOptions?.configFile === false) {
 return;
 }
 const configFile = findConfigToLoad(viteConfig, inlineOptions);
@@ -38,7 +39,10 @@ export async function loadSvelteConfig(
 // try to use dynamic import for svelte.config.js first
 if (configFile.endsWith('.js') || configFile.endsWith('.mjs')) {
 try {
-const result = await dynamicImportDefault(pathToFileURL(configFile).href);
+const result = await dynamicImportDefault(
+pathToFileURL(configFile).href,
+fs.statSync(configFile).mtimeMs
+);
 if (result != null) {
 return {
 ...result,
@@ -83,9 +87,9 @@ export async function loadSvelteConfig(
 }
 }
 
-function findConfigToLoad(viteConfig: UserConfig, inlineOptions: Partial<Options>) {
-const root = viteConfig.root || process.cwd();
-if (inlineOptions.configFile) {
+function findConfigToLoad(viteConfig?: UserConfig, inlineOptions?: Partial<Options>) {
+const root = viteConfig?.root || process.cwd();
+if (inlineOptions?.configFile) {
 const abolutePath = path.isAbsolute(inlineOptions.configFile)
 ? inlineOptions.configFile
 : path.resolve(root, inlineOptions.configFile);