fix: HMR regression (#1858)

* fix: HMR regression

* fix: inject HMR script directly

.changeset/beige-hairs-design.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix HMR regression

packages/astro/src/core/create-vite.ts

@@ -22,7 +22,7 @@ const ALWAYS_EXTERNAL = new Set([
   'shiki',
   'shorthash',
   'unified',
-  'whatwg-url',
+  'whatwg-url'
 ]);
 const ALWAYS_NOEXTERNAL = new Set([
   'astro', // This is only because Vite's native ESM doesn't resolve "exports" correctly.

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

@@ -225,7 +225,9 @@ export async function render(renderers: Renderer[], mod: ComponentInstance, ssrO
     tags.push({
       tag: 'script',
       attrs: { type: 'module' },
-      children: `import 'astro/runtime/client/hmr.js';`,
+      // HACK: inject the direct contents of our `astro/runtime/client/hmr.js` to ensure 
+      // `import.meta.hot` is properly handled by Vite
+      children: await getHmrScript(),
       injectTo: 'head',
     });
   }
@@ -255,6 +257,15 @@ export async function render(renderers: Renderer[], mod: ComponentInstance, ssrO
   return html;
 }
 
+let hmrScript: string;
+async function getHmrScript() {
+  if (hmrScript) return hmrScript;
+  const filePath = fileURLToPath(new URL('../../runtime/client/hmr.js', import.meta.url));
+  const content = await fs.promises.readFile(filePath);
+  hmrScript = content.toString();
+  return hmrScript;
+}
+
 export async function ssr(ssrOpts: SSROptions): Promise<string> {
   try {
     const [renderers, mod] = await preload(ssrOpts);