perf(next-plugin): prewarm apps whose routes live at the project root

.changepacks/changepack_log_next_root_app.json

@@ -0,0 +1,8 @@
+{
+  "changes": {
+    "packages/next-plugin/package.json": "Patch",
+    "packages/plugin-utils/package.json": "Patch"
+  },
+  "note": "Next apps with `app/` or `pages/` at the project root (no `src/`) are prewarmed and waited on like `src/` apps, so Turbopack production builds no longer fall back to a 2.5 s idle wait before serving the base CSS. Source scans skip dot directories such as `.next` and `.git`",
+  "date": "2026-11-15T00:00:00.000Z"
+}

packages/next-plugin/src/__tests__/plugin.test.ts

@@ -439,6 +439,28 @@ describe('DevupUINextPlugin', () => {
       })
     })
 
+    it('reads routes from the project root when it holds app or pages', () => {
+      // Given: a Next app with `app/` at the root and no `src/`.
+      existsSyncSpy.mockImplementation(
+        (path: fs.PathLike) => String(path) === resolve('app'),
+      )
+      const graphSpy = spyOn(
+        importGraphModule,
+        'buildStaticImportGraph',
+      ).mockReturnValue(createSingleFileGraph(resolve('app/page.tsx')))
+      try {
+        // When
+        DevupUI({}).webpack!(createWebpackConfig(), createWebpackContext())
+        // Then
+        expect(graphSpy).toHaveBeenCalledWith(
+          process.cwd(),
+          resolve('tsconfig.json'),
+        )
+      } finally {
+        graphSpy.mockRestore()
+      }
+    })
+
     it('should apply webpack plugin with dev', async () => {
       const ret = DevupUI({})
 
@@ -1027,6 +1049,26 @@ export const box = style({ color: 'red' })`
         expect.objectContaining({ sourceMap: true }),
       )
     })
+    it('keeps configuring Turbopack when the import graph cannot be read', () => {
+      process.env.TURBOPACK = '1'
+      process.env.DEVUP_UI_PROFILE = '1'
+      const graphSpy = spyOn(
+        importGraphModule,
+        'buildStaticImportGraph',
+      ).mockImplementation(() => {
+        throw new Error('unreadable')
+      })
+      const profileSpy = spyOn(console, 'info').mockImplementation(() => {})
+      try {
+        expect(DevupUI({}).turbopack?.rules).toBeDefined()
+        expect(profileSpy).toHaveBeenCalledWith(
+          expect.stringContaining('"failed":true'),
+        )
+      } finally {
+        profileSpy.mockRestore()
+        graphSpy.mockRestore()
+      }
+    })
     it('should create theme.d.ts file', async () => {
       process.env.TURBOPACK = '1'
       existsSyncSpy.mockReturnValue(true)

packages/next-plugin/src/plugin.ts

@@ -125,6 +125,16 @@ export function resetTurboSetupCacheForTesting(): void {
   productionTurboSetupOwner = `${performance.timeOrigin}-${Math.random()}`
 }
 
+/**
+ * The directory Next reads routes from: the project root when it holds `app`
+ * or `pages`, otherwise `src`, as Next itself decides.
+ */
+function sourceDir(cwd: string): string {
+  return ['app', 'pages'].some((dir) => existsSync(resolve(cwd, dir)))
+    ? cwd
+    : resolve(cwd, 'src')
+}
+
 /**
  * Devup UI Next Plugin
  * @param config
@@ -302,7 +312,7 @@ export function DevupUI(
     let staticGraph: StaticImportGraph | undefined
     const graphStartedAt = profileStart()
     try {
-      const srcDir = resolve(process.cwd(), 'src')
+      const srcDir = sourceDir(process.cwd())
       const tsconfigPath = resolve(process.cwd(), 'tsconfig.json')
       const cwd = process.cwd()
       // One scan+parse of the source tree, shared by all three consumers below.
@@ -638,7 +648,7 @@ export function DevupUI(
     )
     if (!_options.dev && productionPrewarmFiles === undefined) {
       const cwd = process.cwd()
-      const srcDir = resolve(cwd, 'src')
+      const srcDir = sourceDir(cwd)
       const tsconfigPath = resolve(cwd, 'tsconfig.json')
       const graph = buildStaticImportGraph(srcDir, tsconfigPath)
       productionPrewarmFiles = collectProductionPrewarmFiles({

packages/plugin-utils/src/__tests__/numbering.test.ts

@@ -24,6 +24,7 @@ describe('collectNumberedFiles', () => {
     write('src/a.tsx')
     write('src/nested/c.ts')
     write('src/readme.md')
+    write('src/.cache/skipped.tsx')
     write('node_modules/@acme/ui/Button.tsx')
     write('node_modules/@acme/ui/node_modules/dep/skipped.tsx')
   })

packages/plugin-utils/src/import-graph.ts

@@ -610,7 +610,8 @@ export function compareCodePoints(a: string, b: string): number {
 
 /**
  * Enumerate every extractable source file under `srcDir`, sorted by POSIX path
- * (deterministic order). Skips `node_modules`, test/spec files, and non-JS/TS
+ * (deterministic order). Skips `node_modules`, dot directories such as
+ * `.next` and `.git`, test/spec files, and non-JS/TS
  * files — the SAME filter `buildCanonicalMap` uses internally, so a plugin can
  * pre-warm the extractor over exactly the file set the canonical map was built
  * from. Returns absolute paths.
@@ -635,7 +636,8 @@ export function listSourceFiles(
     for (const entry of entries) {
       const entryPath = join(dir, entry.name)
       if (entry.isDirectory()) {
-        if (entry.name === 'node_modules') continue
+        if (entry.name === 'node_modules' || entry.name.startsWith('.'))
+          continue
         visit(entryPath)
         continue
       }