fix(scanner): skip svelte components with #snippet

packages/vite/src/node/__tests__/fixtures/scan-svelte/svelte-snippet.svelte

@@ -0,0 +1,7 @@
+<script module>
+  export { mySnippet };
+</script>
+
+{#snippet mySnippet()}
+  snippet!
+{/snippet}

packages/vite/src/node/__tests__/scan.spec.ts

@@ -1,10 +1,22 @@
 import path from 'node:path'
 import { describe, expect, test } from 'vitest'
-import { commentRE, importsRE, scriptRE } from '../optimizer/scan'
+import {
+  ScanEnvironment,
+  commentRE,
+  importsRE,
+  scanImports,
+  scriptRE,
+} from '../optimizer/scan'
 import { multilineCommentsRE, singlelineCommentsRE } from '../utils'
-import { createServer, createServerModuleRunner } from '..'
+import { createServer, createServerModuleRunner, resolveConfig } from '..'
 
 describe('optimizer-scan:script-test', () => {
+  const execScriptRE = (input: string) => {
+    const result = scriptRE.exec(input)
+    scriptRE.lastIndex = 0
+    return result
+  }
+
   const scriptContent = `import { defineComponent } from 'vue'
       import ScriptDevelopPane from './ScriptDevelopPane.vue';
       export default defineComponent({
@@ -14,24 +26,21 @@ describe('optimizer-scan:script-test', () => {
       })`
 
   test('component return value test', () => {
-    scriptRE.lastIndex = 0
-    const [, tsOpenTag, tsContent] = scriptRE.exec(
+    const [, tsOpenTag, tsContent] = execScriptRE(
       `<script lang="ts">${scriptContent}</script>`,
     )!
     expect(tsOpenTag).toEqual('<script lang="ts">')
     expect(tsContent).toEqual(scriptContent)
 
-    scriptRE.lastIndex = 0
-    const [, openTag, content] = scriptRE.exec(
+    const [, openTag, content] = execScriptRE(
       `<script>${scriptContent}</script>`,
     )!
     expect(openTag).toEqual('<script>')
     expect(content).toEqual(scriptContent)
   })
 
   test('include comments test', () => {
-    scriptRE.lastIndex = 0
-    const ret = scriptRE.exec(
+    const ret = execScriptRE(
       `<template>
         <!--  <script >var test1 = null</script> -->
         <!--  <script >var test2 = null</script> -->
@@ -41,35 +50,26 @@ describe('optimizer-scan:script-test', () => {
   })
 
   test('components with script keyword test', () => {
-    scriptRE.lastIndex = 0
-    let ret = scriptRE.exec(`<template><script-develop-pane/></template>`)
+    let ret = execScriptRE(`<template><script-develop-pane/></template>`)
     expect(ret).toBe(null)
 
-    scriptRE.lastIndex = 0
-    ret = scriptRE.exec(
+    ret = execScriptRE(
       `<template><script-develop-pane></script-develop-pane></template>`,
     )
     expect(ret).toBe(null)
 
-    scriptRE.lastIndex = 0
-    ret = scriptRE.exec(
+    ret = execScriptRE(
       `<template><script-develop-pane  > content </script-develop-pane></template>`,
     )
     expect(ret).toBe(null)
   })
 
   test('ordinary script tag test', () => {
-    scriptRE.lastIndex = 0
-    const [, tag, content] = scriptRE.exec(
-      `<script  >var test = null</script>`,
-    )!
+    const [, tag, content] = execScriptRE(`<script  >var test = null</script>`)!
     expect(tag).toEqual('<script  >')
     expect(content).toEqual('var test = null')
 
-    scriptRE.lastIndex = 0
-    const [, tag1, content1] = scriptRE.exec(
-      `<script>var test = null</script>`,
-    )!
+    const [, tag1, content1] = execScriptRE(`<script>var test = null</script>`)!
     expect(tag1).toEqual('<script>')
     expect(content1).toEqual('var test = null')
   })
@@ -126,6 +126,25 @@ describe('optimizer-scan:script-test', () => {
   })
 })
 
+test('scan svelte', async () => {
+  const config = await resolveConfig(
+    {
+      configFile: false,
+      root: path.join(import.meta.dirname, 'fixtures', 'scan-svelte'),
+      optimizeDeps: {
+        include: [],
+        entries: ['./svelte-snippet.svelte'],
+        extensions: ['.svelte'],
+      },
+    },
+    'serve',
+  )
+  const environment = new ScanEnvironment('client', config)
+  await environment.init()
+  const { result } = scanImports(environment)
+  await result
+})
+
 test('scan jsx-runtime', async (ctx) => {
   const server = await createServer({
     configFile: false,

packages/vite/src/node/optimizer/scan.ts

@@ -477,6 +477,12 @@ function esbuildScanPlugin(
         external: true,
       }))
 
+      // dummy module for Svelte file with snippets
+      build.onResolve({ filter: /^svelte-snippet-dummy:/ }, ({ path }) => ({
+        path,
+        external: true,
+      }))
+
       // local scripts (`<script>` in Svelte and `<script setup>` in Vue)
       build.onResolve({ filter: virtualModuleRE }, ({ path }) => {
         return {
@@ -604,6 +610,11 @@ function esbuildScanPlugin(
               if (!isModule) {
                 addedImport = true
                 js += `import ${virtualModulePath}\n`
+              } else if (raw.includes('#snippet')) {
+                // <script module> in files with #snippet contains exports that are not declared
+                // skip scanning the script content
+                addedImport = true
+                js += `export * from 'svelte-snippet-dummy:${normalizePath(p)}'\n`
               }
             }