refactor: tsup outExtension migration compatibility

__snapshots__/tsnapi/config.snapshot.d.ts

@@ -43,6 +43,7 @@ export interface UserConfig {
   bundle?: boolean;
   fixedExtension?: boolean;
   outExtensions?: OutExtensionFactory;
+  outExtension?: OutExtensionFactory;
   hash?: boolean;
   cjsDefault?: boolean;
   outputOptions?: OutputOptions | ((_: OutputOptions, _: NormalizedFormat, _: {

__snapshots__/tsnapi/index.snapshot.d.ts

@@ -171,6 +171,7 @@ export interface UserConfig {
   bundle?: boolean;
   fixedExtension?: boolean;
   outExtensions?: OutExtensionFactory;
+  outExtension?: OutExtensionFactory;
   hash?: boolean;
   cjsDefault?: boolean;
   outputOptions?: OutputOptions | ((_: OutputOptions, _: NormalizedFormat, _: {
@@ -222,7 +223,7 @@ export type NoExternalFn = (_: string, _: string | undefined) => boolean | null
 export type NormalizedFormat = InternalModuleFormat;
 export type OutExtensionFactory = (_: OutExtensionContext) => OutExtensionObject | undefined;
 export type PackageType = "module" | "commonjs" | undefined;
-export type ResolvedConfig = Overwrite<MarkPartial<Omit<UserConfig, "workspace" | "fromVite" | "publicDir" | "bundle" | "injectStyle" | "removeNodeProtocol" | "external" | "noExternal" | "inlineOnly" | "skipNodeModulesBundle" | "logLevel" | "failOnWarn" | "customLogger" | "envFile" | "envPrefix">, "globalName" | "inputOptions" | "outputOptions" | "minify" | "define" | "alias" | "onSuccess" | "outExtensions" | "hooks" | "copy" | "loader" | "name" | "banner" | "footer" | "checks" | "css">, {
+export type ResolvedConfig = Overwrite<MarkPartial<Omit<UserConfig, "workspace" | "fromVite" | "publicDir" | "bundle" | "injectStyle" | "removeNodeProtocol" | "outExtension" | "external" | "noExternal" | "inlineOnly" | "skipNodeModulesBundle" | "logLevel" | "failOnWarn" | "customLogger" | "envFile" | "envPrefix">, "globalName" | "inputOptions" | "outputOptions" | "minify" | "define" | "alias" | "onSuccess" | "outExtensions" | "hooks" | "copy" | "loader" | "name" | "banner" | "footer" | "checks" | "css">, {
   entry: Record<string, string>;
   rawEntry?: TsdownInputOption;
   nameLabel: string | undefined;

docs/guide/migrate-from-tsup.md

@@ -54,10 +54,11 @@ While `tsdown` aims to be highly compatible with `tsup`, there are some differen
 
 Some options have been renamed for clarity:
 
-| tsup             | tsdown       | Notes                              |
-| ---------------- | ------------ | ---------------------------------- |
-| `cjsInterop`     | `cjsDefault` | CJS default export handling        |
-| `esbuildPlugins` | `plugins`    | Now uses Rolldown/Unplugin plugins |
+| tsup             | tsdown          | Notes                              |
+| ---------------- | --------------- | ---------------------------------- |
+| `cjsInterop`     | `cjsDefault`    | CJS default export handling        |
+| `esbuildPlugins` | `plugins`       | Now uses Rolldown/Unplugin plugins |
+| `outExtension`   | `outExtensions` | Custom output extensions           |
 
 ### Deprecated but Compatible Options
 
@@ -76,6 +77,19 @@ The following tsup options still work in tsdown for backward compatibility, but
 
 tsdown also adds `deps.onlyBundle` for whitelisting allowed bundled packages.
 
+### Output Filename Differences
+
+For IIFE builds, `tsdown` emits names like `[name].iife.js`, while `tsup` commonly emitted `[name].global.js`. `outExtensions` customizes output extensions or suffixes, but it does not remove the built-in `.iife` or `.umd` segment. To preserve older full filename patterns, use Rolldown output options:
+
+```ts
+export default {
+  format: 'iife',
+  outputOptions: {
+    entryFileNames: '[name].global.js',
+  },
+}
+```
+
 ### Plugin System
 
 tsdown uses [Rolldown](https://rolldown.rs/) plugins instead of esbuild plugins. If you use [unplugin](https://github.com/unjs/unplugin) plugins, update the import path:

docs/options/output-format.md

@@ -32,6 +32,9 @@ tsdown --format iife
 > [!NOTE]
 > **CJS is in maintenance-only mode.** Since the ecosystem is transitioning to ESM and Node.js now supports `require(esm)`, `tsdown`'s CJS-specific features (such as [`cjsDefault`](./cjs-default.md)) are kept for compatibility but will not be further enhanced or optimized. New libraries are encouraged to publish ESM-only.
 
+> [!NOTE]
+> IIFE and UMD outputs include the format in their filenames by default, such as `index.iife.js` and `index.umd.js`. If you need a custom full filename pattern, set `outputOptions.entryFileNames`.
+
 ## Overriding Configuration by Format
 
 You can override specific configuration options for each output format by setting `format` as an object in your config file. This allows you to tailor settings such as `target` or other options for each format individually.

docs/zh-CN/guide/migrate-from-tsup.md

@@ -54,10 +54,11 @@ npx tsdown-migrate packages/foo packages/bar
 
 部分选项已重命名以提高清晰度：
 
-| tsup             | tsdown       | 说明                          |
-| ---------------- | ------------ | ----------------------------- |
-| `cjsInterop`     | `cjsDefault` | CJS 默认导出处理              |
-| `esbuildPlugins` | `plugins`    | 现使用 Rolldown/Unplugin 插件 |
+| tsup             | tsdown          | 说明                          |
+| ---------------- | --------------- | ----------------------------- |
+| `cjsInterop`     | `cjsDefault`    | CJS 默认导出处理              |
+| `esbuildPlugins` | `plugins`       | 现使用 Rolldown/Unplugin 插件 |
+| `outExtension`   | `outExtensions` | 自定义输出扩展名              |
 
 ### 已弃用但兼容的选项
 
@@ -76,6 +77,19 @@ npx tsdown-migrate packages/foo packages/bar
 
 tsdown 还新增了 `deps.onlyBundle`，用于白名单指定允许打包的依赖。
 
+### 输出文件名差异
+
+对于 IIFE 构建，`tsdown` 会输出类似 `[name].iife.js` 的文件名，而 `tsup` 常见输出是 `[name].global.js`。`outExtensions` 用于自定义输出扩展名或后缀，但不会移除内置的 `.iife` 或 `.umd` 片段。如果需要保留旧的完整文件名模式，请使用 Rolldown 的输出选项：
+
+```ts
+export default {
+  format: 'iife',
+  outputOptions: {
+    entryFileNames: '[name].global.js',
+  },
+}
+```
+
 ### 插件系统
 
 tsdown 使用 [Rolldown](https://rolldown.rs/) 插件代替 esbuild 插件。如果您使用 [unplugin](https://github.com/unjs/unplugin) 插件，需更新导入路径：

docs/zh-CN/options/output-format.md

@@ -32,6 +32,9 @@ tsdown --format iife
 > [!NOTE]
 > **CJS 处于仅维护模式。** 由于生态系统正在向 ESM 迁移，且 Node.js 已支持 `require(esm)`，`tsdown` 中 CJS 专属的功能（例如 [`cjsDefault`](./cjs-default.md)）仅保留以确保兼容性，不会再进一步增强或优化。建议新库直接发布为 ESM-only。
 
+> [!NOTE]
+> IIFE 和 UMD 输出默认会在文件名中包含格式片段，例如 `index.iife.js` 和 `index.umd.js`。如果需要自定义完整文件名模式，请设置 `outputOptions.entryFileNames`。
+
 ## 按格式覆盖配置
 
 您可以在配置文件中将 `format` 设置为对象，从而为每种输出格式单独覆盖特定配置选项。这允许您为每个格式分别定制如 `target` 等设置。

packages/migrate/src/helpers/__snapshots__/tsup-config.test.ts.snap

@@ -141,6 +141,28 @@ exports[`option transformations > entryPoints should transform to entry > code 1
 }"
 `;
 
+exports[`option transformations > outExtension method should transform to outExtensions > code 1`] = `
+"export default {
+  format: 'esm',
+  outExtensions() {
+    return { js: '.mjs' }
+  },
+  clean: false,
+  dts: false,
+  target: false,
+}"
+`;
+
+exports[`option transformations > outExtension property should transform to outExtensions > code 1`] = `
+"export default {
+  format: 'esm',
+  outExtensions: () => ({ js: '.mjs' }),
+  clean: false,
+  dts: false,
+  target: false,
+}"
+`;
+
 exports[`option transformations > publicDir should transform to copy > code 1`] = `
 "export default {
   copy: 'public',

packages/migrate/src/helpers/tsup-config.test.ts

@@ -107,6 +107,34 @@ describe('option transformations', () => {
     expect(code).not.toContain('publicDir')
   })
 
+  test('outExtension property should transform to outExtensions', () => {
+    const input = `
+      export default {
+        format: 'esm',
+        outExtension: () => ({ js: '.mjs' }),
+      }
+    `
+    const { code } = transform(input, 'tsup.config.ts')
+    expect(code).toContain('outExtensions:')
+    expect(code).toContain("js: '.mjs'")
+    expect(code).not.toContain('outExtension:')
+  })
+
+  test('outExtension method should transform to outExtensions', () => {
+    const input = `
+      export default {
+        format: 'esm',
+        outExtension() {
+          return { js: '.mjs' }
+        },
+      }
+    `
+    const { code } = transform(input, 'tsup.config.ts')
+    expect(code).toContain('outExtensions()')
+    expect(code).toContain("js: '.mjs'")
+    expect(code).not.toContain('outExtension()')
+  })
+
   test('removeNodeProtocol should transform to nodeProtocol: "strip"', () => {
     const input = `
       export default {

packages/migrate/src/helpers/tsup-config.ts

@@ -30,6 +30,7 @@ const WARNING_MESSAGES: Record<string, string> = {
 const PROPERTY_RENAMES: Record<string, string> = {
   entryPoints: 'entry',
   esbuildPlugins: 'plugins',
+  outExtension: 'outExtensions',
   publicDir: 'copy',
   cjsInterop: 'cjsDefault',
 }
@@ -101,24 +102,34 @@ export function transformTsupConfig(
     edits.push(node.replace(text.replace('/esbuild', '/rolldown')))
   }
 
-  // Helper: Find property identifier (key only) by name using relational rule
-  const findPropertyIdentifier = (propName: string): SgNode | null => {
-    return root.find({
+  // Helper: Find property identifiers (keys only) by name using relational rules
+  const findPropertyIdentifiers = (propName: string): SgNode[] => {
+    return root.findAll({
       rule: {
-        kind: 'property_identifier',
-        regex: `^${propName}$`,
-        inside: {
-          kind: 'pair',
-          field: 'key',
-        },
+        any: [
+          {
+            kind: 'property_identifier',
+            regex: `^${propName}$`,
+            inside: {
+              kind: 'pair',
+              field: 'key',
+            },
+          },
+          {
+            kind: 'property_identifier',
+            regex: `^${propName}$`,
+            inside: {
+              kind: 'method_definition',
+            },
+          },
+        ],
       },
     })
   }
 
   // 3. Rename properties using AST - only replace the key identifier
   for (const [oldName, newName] of Object.entries(PROPERTY_RENAMES)) {
-    const propIdentifier = findPropertyIdentifier(oldName)
-    if (propIdentifier) {
+    for (const propIdentifier of findPropertyIdentifiers(oldName)) {
       edits.push(propIdentifier.replace(newName))
     }
   }

skills/tsdown-migrate/SKILL.md

@@ -69,6 +69,7 @@ Replace all identifiers: `tsup` → `tsdown`, `TSUP` → `TSDOWN`.
 |------|--------|-------|
 | `cjsInterop` | `cjsDefault` | CJS default export handling |
 | `esbuildPlugins` | `plugins` | Now uses Rolldown/Unplugin plugins |
+| `outExtension` | `outExtensions` | Custom output extensions |
 
 ### Deprecated but Compatible
 
@@ -87,6 +88,10 @@ These tsup options still work in tsdown for backward compatibility, but emit dep
 | `noExternal: [...]` | `deps: { alwaysBundle: [...] }` | Moved to deps namespace |
 | `skipNodeModulesBundle` | `deps: { skipNodeModulesBundle: true }` | Moved to deps namespace |
 
+### Output Filename Differences
+
+For IIFE builds, `tsdown` emits names like `[name].iife.js`, while `tsup` commonly emitted `[name].global.js`. `outExtensions` customizes extensions or suffixes, but it does not remove the built-in `.iife` or `.umd` segment. Use `outputOptions.entryFileNames: '[name].global.js'` to preserve old IIFE filenames.
+
 ### Dependency Namespace Moves
 
 Dependencies config moved under `deps` namespace. If both `external` and `noExternal` exist, merge into a single `deps` object:
@@ -235,7 +240,7 @@ Use this checklist when performing a migration:
 - [ ] Rename tsup.config.* → tsdown.config.*
 - [ ] Update import from 'tsup' to 'tsdown'
 - [ ] Replace tsup/TSUP identifiers with tsdown/TSDOWN
-- [ ] Apply property renames (cjsInterop→cjsDefault, esbuildPlugins→plugins)
+- [ ] Apply property renames (cjsInterop→cjsDefault, esbuildPlugins→plugins, outExtension→outExtensions)
 - [ ] Migrate deprecated options (publicDir→copy, bundle→unbundle, removeNodeProtocol→nodeProtocol, injectStyle→css.inject)
 - [ ] Move external/noExternal/skipNodeModulesBundle into deps namespace
 - [ ] Update unplugin imports from /esbuild to /rolldown

skills/tsdown-migrate/references/guide-differences-detailed.md

@@ -45,6 +45,7 @@ Comprehensive comparison of tsdown and tsup for understanding migration impact a
 |---------|------|--------|--------|
 | CJS interop | `cjsInterop` | `cjsDefault` | Property rename |
 | Plugins | `esbuildPlugins` | `plugins` | Different plugin format (Rolldown) |
+| Output extensions | `outExtension` | `outExtensions` | Property rename |
 
 ### Deprecated but Compatible
 
@@ -61,6 +62,10 @@ These tsup options still work in tsdown but emit deprecation warnings. They will
 | Inline deps | `noExternal` | `deps.alwaysBundle` | Moved to deps namespace |
 | Skip node_modules | `skipNodeModulesBundle` | `deps.skipNodeModulesBundle` | Moved to deps namespace |
 
+### Output Filename Differences
+
+For IIFE builds, `tsdown` emits `[name].iife.js`; `tsup` commonly emitted `[name].global.js`. `outExtensions` customizes extensions or suffixes, but it does not remove `.iife` or `.umd`. Use `outputOptions.entryFileNames` for full filename patterns.
+
 ### Not Supported
 
 | Feature | Reason | Alternative |

skills/tsdown-migrate/references/guide-option-mappings.md

@@ -38,6 +38,10 @@ export default defineConfig({
 
 Note: All `unplugin-*/esbuild` imports must change to `unplugin-*/rolldown`.
 
+### outExtension → outExtensions
+
+`outExtension` was renamed to `outExtensions`.
+
 ## Deprecated but Compatible
 
 These options still work in tsdown for backward compatibility but emit deprecation warnings. Migrate them immediately — they will be removed in a future version.

skills/tsdown/references/guide-migrate-from-tsup.md

@@ -42,6 +42,16 @@ npx tsdown-migrate packages/foo packages/bar
 | `dts` | `false` | Auto-enabled if `types`/`typings` in package.json |
 | `target` | Manual | Auto-read from `engines.node` in package.json |
 
+### Option Renames
+
+| tsup | tsdown |
+|------|--------|
+| `outExtension` | `outExtensions` |
+
+### Output Filename Differences
+
+For IIFE builds, `tsdown` emits `[name].iife.js`; `tsup` commonly emitted `[name].global.js`. `outExtensions` customizes extensions or suffixes, but it does not remove `.iife` or `.umd`. Use `outputOptions.entryFileNames: '[name].global.js'` to preserve old IIFE filenames.
+
 ### New Features in tsdown
 
 #### Node Protocol Control

skills/tsdown/references/option-output-directory.md

@@ -122,9 +122,11 @@ export default defineConfig({
 |--------|-------------------|----------------------|
 | `esm` | `.mjs` | `.js` |
 | `cjs` | `.cjs` | `.js` |
-| `iife` | `.global.js` | `.global.js` |
+| `iife` | `.iife.js` | `.iife.js` |
 | `umd` | `.umd.js` | `.umd.js` |
 
+For IIFE/UMD builds, `outExtensions` customizes extensions or suffixes but does not remove the built-in `.iife` or `.umd` segment. Use `outputOptions.entryFileNames` for custom full filename patterns.
+
 ### ESM with .js Extension
 
 ```ts

skills/tsdown/references/option-output-format.md

@@ -99,7 +99,7 @@ export default defineConfig({
 })
 ```
 
-Output: `dist/index.global.js` (IIFE with global `MyLib`)
+Output: `dist/index.iife.js` (IIFE with global `MyLib`)
 
 ### Universal Library (UMD)
 
@@ -147,9 +147,11 @@ export default defineConfig({
 |--------|-----------|
 | ESM | `.mjs` or `.js` (with `"type": "module"`) |
 | CJS | `.cjs` or `.js` (without `"type": "module"`) |
-| IIFE | `.global.js` |
+| IIFE | `.iife.js` |
 | UMD | `.umd.js` |
 
+For custom IIFE filenames, set `outputOptions.entryFileNames`. `outExtensions` customizes extensions or suffixes but does not remove `.iife` or `.umd`.
+
 ### Customize Extensions
 
 Use `outExtensions` to override:

src/config/options.ts

@@ -103,6 +103,8 @@ export async function resolveUserConfig(
     globImport = true,
     css,
     injectStyle,
+    outExtension,
+    outExtensions,
     fixedExtension = platform === 'node',
     devtools = false,
     write = true,
@@ -222,6 +224,18 @@ export async function resolveUserConfig(
     }
   }
 
+  if (outExtension) {
+    if (outExtensions) {
+      throw new TypeError(
+        '`outExtension` is deprecated. Cannot be used with `outExtensions`',
+      )
+    }
+    logger.warn(
+      `${blue`outExtension`} is deprecated. Use ${blue`outExtensions`} instead.`,
+    )
+    outExtensions = outExtension
+  }
+
   envPrefix = toArray(envPrefix)
   if (envPrefix.includes('')) {
     logger.warn(
@@ -326,6 +340,7 @@ export async function resolveUserConfig(
     nameLabel,
     nodeProtocol,
     outDir,
+    outExtensions,
     pkg,
     platform,
     plugins,