fix: skip injecting __vite__mapDeps when it's not used (#16271)

packages/vite/src/node/plugins/importAnalysisBuild.ts

@@ -498,20 +498,23 @@ export function buildImportAnalysisPlugin(config: ResolvedConfig): Plugin {
                 s.update(
                   markerStartPos,
                   markerStartPos + preloadMarker.length + 2,
-                  `__vite__mapDeps([${renderedDeps.join(',')}])`,
+                  renderedDeps.length > 0
+                    ? `__vite__mapDeps([${renderedDeps.join(',')}])`
+                    : `[]`,
                 )
                 rewroteMarkerStartPos.add(markerStartPos)
               }
             }
           }
 
-          const fileDepsCode = `[${fileDeps
-            .map((fileDep) =>
-              fileDep.runtime ? fileDep.url : JSON.stringify(fileDep.url),
-            )
-            .join(',')}]`
+          if (fileDeps.length > 0) {
+            const fileDepsCode = `[${fileDeps
+              .map((fileDep) =>
+                fileDep.runtime ? fileDep.url : JSON.stringify(fileDep.url),
+              )
+              .join(',')}]`
 
-          const mapDepsCode = `\
+            const mapDepsCode = `\
 function __vite__mapDeps(indexes) {
   if (!__vite__mapDeps.viteFileDeps) {
     __vite__mapDeps.viteFileDeps = ${fileDepsCode}
@@ -519,11 +522,12 @@ function __vite__mapDeps(indexes) {
   return indexes.map((i) => __vite__mapDeps.viteFileDeps[i])
 }\n`
 
-          // inject extra code at the top or next line of hashbang
-          if (code.startsWith('#!')) {
-            s.prependLeft(code.indexOf('\n') + 1, mapDepsCode)
-          } else {
-            s.prepend(mapDepsCode)
+            // inject extra code at the top or next line of hashbang
+            if (code.startsWith('#!')) {
+              s.prependLeft(code.indexOf('\n') + 1, mapDepsCode)
+            } else {
+              s.prepend(mapDepsCode)
+            }
           }
 
           // there may still be markers due to inlined dynamic imports, remove

playground/js-sourcemap/__tests__/js-sourcemap.spec.ts

@@ -152,9 +152,22 @@ describe.runIf(isBuild)('build tests', () => {
       }
     `)
     // verify sourcemap comment is preserved at the last line
-    const js = findAssetFile(/after-preload-dynamic.*\.js$/)
+    const js = findAssetFile(/after-preload-dynamic-[-\w]{8}\.js$/)
     expect(js).toMatch(
-      /\n\/\/# sourceMappingURL=after-preload-dynamic.*\.js\.map\n$/,
+      /\n\/\/# sourceMappingURL=after-preload-dynamic-[-\w]{8}\.js\.map\n$/,
     )
   })
+
+  test('__vite__mapDeps injected after banner', async () => {
+    const js = findAssetFile(/after-preload-dynamic-hashbang-[-\w]{8}\.js$/)
+    expect(js.split('\n').slice(0, 2)).toEqual([
+      '#!/usr/bin/env node',
+      'function __vite__mapDeps(indexes) {',
+    ])
+  })
+
+  test('no unused __vite__mapDeps', async () => {
+    const js = findAssetFile(/after-preload-dynamic-no-dep-[-\w]{8}\.js$/)
+    expect(js).not.toMatch(/__vite__mapDeps/)
+  })
 })

playground/js-sourcemap/after-preload-dynamic-no-dep.js

@@ -0,0 +1,3 @@
+import('./dynamic/dynamic-no-dep')
+
+console.log('after preload dynamic no dep')

playground/js-sourcemap/dynamic/dynamic-no-dep.js

@@ -0,0 +1 @@
+console.log('dynamic/dynamic-no-dep')

playground/js-sourcemap/index.html

@@ -7,5 +7,6 @@
 <script type="module" src="./bar.ts"></script>
 <script type="module" src="./after-preload-dynamic.js"></script>
 <script type="module" src="./after-preload-dynamic-hashbang.js"></script>
+<script type="module" src="./after-preload-dynamic-no-dep.js"></script>
 <script type="module" src="./with-multiline-import.ts"></script>
 <script type="module" src="./zoo.js"></script>

playground/js-sourcemap/vite.config.js

@@ -18,6 +18,9 @@ export default defineConfig({
           if (name.endsWith('after-preload-dynamic-hashbang.js')) {
             return 'after-preload-dynamic-hashbang'
           }
+          if (name.endsWith('after-preload-dynamic-no-dep.js')) {
+            return 'after-preload-dynamic-no-dep'
+          }
         },
         banner(chunk) {
           if (chunk.name.endsWith('after-preload-dynamic-hashbang')) {