Fix outExtension for dts files

src/api-extractor.ts

@@ -98,7 +98,9 @@ async function rollupDtsFiles(
   const declarationDir = ensureTempDeclarationDir()
   const outDir = options.outDir || 'dist'
   const pkg = await loadPkg(process.cwd())
-  const dtsExtension = defaultOutExtension({ format, pkgType: pkg.type }).dts
+  const dtsExtension =
+    options.outputExtensionMap.get(format)?.dts ||
+    defaultOutExtension({ format, pkgType: pkg.type }).dts
   const tsconfig = options.tsconfig || 'tsconfig.json'
 
   let dtsInputFilePath = path.join(

src/index.ts

@@ -14,6 +14,7 @@ import {
   removeFiles,
   resolveExperimentalDtsConfig,
   resolveInitialExperimentalDtsConfig,
+  resolveOutputExtensionMap,
   slash,
 } from './utils'
 import { createLogger, setSilent } from './log'
@@ -77,14 +78,17 @@ const normalizeOptions = async (
     ...optionsOverride,
   }
 
+  const formats =
+    typeof _options.format === 'string'
+      ? [_options.format]
+      : _options.format || ['cjs']
+
   const options: Partial<NormalizedOptions> = {
     outDir: 'dist',
     removeNodeProtocol: true,
     ..._options,
-    format:
-      typeof _options.format === 'string'
-        ? [_options.format as Format]
-        : _options.format || ['cjs'],
+    format: formats,
+
     dts:
       typeof _options.dts === 'boolean'
         ? _options.dts
@@ -161,6 +165,10 @@ const normalizeOptions = async (
     options.target = 'node16'
   }
 
+  options.outputExtensionMap = await resolveOutputExtensionMap(
+    options as NormalizedOptions,
+  )
+
   return options as NormalizedOptions
 }
 

src/options.ts

@@ -272,4 +272,11 @@ export type NormalizedOptions = Omit<
   tsconfigResolvePaths: Record<string, string[]>
   tsconfigDecoratorMetadata?: boolean
   format: Format[]
+  /**
+   * Custom file extension per each
+   * {@linkcode Format | module format}.
+   *
+   * @since 8.4.0
+   */
+  outputExtensionMap: Map<Format, OutExtensionObject>
 }

src/rollup.ts

@@ -156,7 +156,7 @@ const getRollupConfig = async (
     },
     outputConfig: options.format.map((format): OutputOptions => {
       const outputExtension =
-        options.outExtension?.({ format, options, pkgType: pkg.type }).dts ||
+        options.outputExtensionMap.get(format)?.dts ||
         defaultOutExtension({ format, pkgType: pkg.type }).dts
       return {
         dir: options.outDir || 'dist',

src/utils.ts

@@ -4,6 +4,7 @@ import resolveFrom from 'resolve-from'
 import type { InputOption } from 'rollup'
 import strip from 'strip-json-comments'
 import { glob } from 'tinyglobby'
+import { loadPkg } from './load'
 import type {
   Entry,
   Format,
@@ -422,3 +423,40 @@ export const resolveInitialExperimentalDtsConfig = async (
         : await resolveEntryPaths(experimentalDts.entry),
   }
 }
+
+/**
+ * Resolves the
+ * {@linkcode NormalizedOptions.outputExtensionMap | output extension map}
+ * for each specified {@linkcode Format | format}
+ * in the provided {@linkcode options}.
+ *
+ * @param options - The normalized options containing format and output extension details.
+ * @returns A {@linkcode Promise | promise} that resolves to a {@linkcode Map}, where each key is a {@linkcode Format | format} and each value is an object containing the resolved output extensions for both `js` and `dts` files.
+ *
+ * @internal
+ */
+export const resolveOutputExtensionMap = async (
+  options: NormalizedOptions,
+): Promise<NormalizedOptions['outputExtensionMap']> => {
+  const pkg = await loadPkg(process.cwd())
+
+  const formatOutExtension = new Map(
+    options.format.map((format) => {
+      const outputExtensions = options.outExtension?.({
+        format,
+        options,
+        pkgType: pkg.type,
+      })
+
+      return [
+        format,
+        {
+          ...defaultOutExtension({ format, pkgType: pkg.type }),
+          ...(outputExtensions || {}),
+        },
+      ] as const
+    }),
+  )
+
+  return formatOutExtension
+}

test/dts.test.ts

@@ -480,3 +480,58 @@ test('declaration files with multiple entrypoints #316', async () => {
     'dist/bar/index.d.ts',
   ).toMatchSnapshot()
 })
+
+test('custom dts output extension', async ({ expect, task }) => {
+  const { outFiles } = await run(
+    getTestName(),
+    {
+      'src/types.ts': `export type Person = { name: string }`,
+      'src/index.ts': `export const foo = [1, 2, 3]\nexport type { Person } from './types'`,
+      'tsup.config.ts': `export default {
+        name: '${task.name}',
+        entry: { index: 'src/index.ts' },
+        dts: true,
+        format: ['esm', 'cjs'],
+        outExtension({ format }) {
+          return {
+            js: format === 'esm' ? '.cjs' : '.mjs',
+            dts: format === 'esm' ? '.d.cts' : '.d.mts',
+          }
+        },
+    }`,
+      'package.json': JSON.stringify(
+        {
+          name: 'custom-dts-output-extension',
+          description: task.name,
+          type: 'module',
+        },
+        null,
+        2,
+      ),
+      'tsconfig.json': JSON.stringify(
+        {
+          compilerOptions: {
+            outDir: './dist',
+            rootDir: './src',
+            moduleResolution: 'Bundler',
+            module: 'ESNext',
+            strict: true,
+            skipLibCheck: true,
+          },
+          include: ['src'],
+        },
+        null,
+        2,
+      ),
+    },
+    {
+      entry: [],
+    },
+  )
+  expect(outFiles).toStrictEqual([
+    'index.cjs',
+    'index.d.cts',
+    'index.d.mts',
+    'index.mjs',
+  ])
+})

test/experimental-dts.test.ts

@@ -604,3 +604,64 @@ test('experimentalDts.entry can be a string of glob pattern', async ({
     ),
   )
 })
+
+test('custom outExtension works with experimentalDts', async ({
+  expect,
+  task,
+}) => {
+  const { outFiles } = await run(
+    getTestName(),
+    {
+      'src/types.ts': `export type Person = { name: string }`,
+      'src/index.ts': `export const foo = [1, 2, 3]\nexport type { Person } from './types'`,
+      'tsup.config.ts': `export default {
+        name: '${task.name}',
+        entry: { index: 'src/index.ts' },
+        format: ['esm', 'cjs'],
+        experimentalDts: true,
+        outExtension({ format }) {
+          return {
+            js: format === 'cjs' ? '.cjs' : '.mjs',
+            dts: format === 'cjs' ? '.d.cts' : '.d.mts',
+          }
+        },
+      }`,
+      'package.json': JSON.stringify(
+        {
+          name: 'custom-dts-output-extension-with-experimental-dts',
+          description: task.name,
+          type: 'module',
+        },
+        null,
+        2,
+      ),
+      'tsconfig.json': JSON.stringify(
+        {
+          compilerOptions: {
+            outDir: './dist',
+            rootDir: './src',
+            moduleResolution: 'Bundler',
+            module: 'ESNext',
+            strict: true,
+            skipLibCheck: true,
+          },
+          include: ['src'],
+        },
+        null,
+        2,
+      ),
+    },
+    {
+      entry: [],
+    },
+  )
+
+  expect(outFiles).toStrictEqual([
+    '_tsup-dts-rollup.d.cts',
+    '_tsup-dts-rollup.d.mts',
+    'index.cjs',
+    'index.d.cts',
+    'index.d.mts',
+    'index.mjs',
+  ])
+})

test/index.test.ts

@@ -217,7 +217,7 @@ test('onSuccess: use a function from config file', async () => {
             await new Promise((resolve) => {
               setTimeout(() => {
                 console.log('world')
-                resolve('')  
+                resolve('')
               }, 1_000)
             })
           }
@@ -601,7 +601,7 @@ test('use rollup for treeshaking --format cjs', async () => {
       }`,
       'input.tsx': `
       import ReactSelect from 'react-select'
-      
+
       export const Component = (props: {}) => {
         return <ReactSelect {...props} />
       };