fix(migrate): preserve existing tsdown pack wiring

Author: TheAlexLichter

packages/cli/src/migration/__tests__/migrator.spec.ts

@@ -8891,6 +8891,45 @@ export default defineConfig({
       tsdownConfig: false,
     });
   });
+
+  it('preserves a tsdown config already wired to pack under a different import name', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({ name: 'test', devDependencies: { 'vite-plus': 'latest' } }, null, 2),
+    );
+    fs.writeFileSync(
+      path.join(tmpDir, 'vite.config.ts'),
+      `import packConfig from './tsdown.config.js';
+
+export default { pack: packConfig({}) };
+`,
+    );
+    fs.writeFileSync(
+      path.join(tmpDir, 'tsdown.config.ts'),
+      `import { defineConfig } from 'tsdown';
+
+export default defineConfig({ entry: 'src/index.ts' });
+`,
+    );
+
+    const originalViteConfig = fs.readFileSync(path.join(tmpDir, 'vite.config.ts'), 'utf8');
+    const report = createMigrationReport();
+    const result = finalizeCoreMigrationForExistingVitePlus(
+      makeWorkspaceInfo(tmpDir, PackageManager.pnpm),
+      true,
+      report,
+    );
+
+    expect(result).toEqual({
+      scripts: false,
+      tsconfigTypes: false,
+      imports: true,
+      tsdownConfig: false,
+    });
+    expect(fs.readFileSync(path.join(tmpDir, 'vite.config.ts'), 'utf8')).toBe(originalViteConfig);
+    expect(report.tsdownImportCount).toBe(0);
+    expect(report.manualSteps).toEqual([]);
+  });
 });
 
 // Regression: templates such as `create-fate` ship a populated vite.config.ts

packages/cli/src/migration/migrator/vite-config.ts

@@ -193,6 +193,29 @@ export function mergeTsdownConfigFile(
 
   // For TS/JS files, import the config file
   const tsdownRelativePath = `./${configs.tsdownConfig}`;
+  // Do not prepend a second `pack` key when the config is already wired under
+  // a different local import name. If a pack config exists but does not import
+  // this tsdown config, leave both files untouched and keep the manual follow-up.
+  if (hasConfigKey(fullViteConfigPath, 'pack')) {
+    const viteConfigContent = fs.readFileSync(fullViteConfigPath, 'utf8');
+    const runtimeImportPath = tsdownRelativePath
+      .replace(/\.mts$/, '.mjs')
+      .replace(/\.cts$/, '.cjs')
+      .replace(/\.ts$/, '.js');
+    const importsTsdownConfig = [tsdownRelativePath, runtimeImportPath].some(
+      (importPath) =>
+        viteConfigContent.includes(`from '${importPath}'`) ||
+        viteConfigContent.includes(`from "${importPath}"`),
+    );
+    if (!importsTsdownConfig) {
+      infoMigration(
+        `Please manually merge ${displayRelative(fullTsdownConfigPath)} into ${displayRelative(fullViteConfigPath)}, see https://viteplus.dev/guide/migrate#tsdown`,
+        report,
+      );
+    }
+    return false;
+  }
+
   const result = mergeTsdownConfig(fullViteConfigPath, tsdownRelativePath);
   if (result.updated) {
     fs.writeFileSync(fullViteConfigPath, result.content);