docs/README.md

@@ -191,7 +191,7 @@ export default defineConfig({
 tsup index.ts --dts
 ```
 
-This will emit `./dist/index.js` and `./dist/index.d.ts`.
+This will emit `./dist/index.js` and `./dist/index.d.ts`. When emitting multiple [bundle formats](#bundle-formats), one declaration file per bundle format is generated. This is required for consumers to get accurate type checking with TypeScript. Note that declaration files generated by any tool other than `tsc` are not guaranteed to be error-free, so it's a good idea to test the output with `tsc` or a tool like [@arethetypeswrong/cli](https://www.npmjs.com/package/@arethetypeswrong/cli) before publishing.
 
 If you have multiple entry files, each entry will get a corresponding `.d.ts` file. So when you only want to generate declaration file for a single entry, use `--dts <entry>` format, e.g. `--dts src/index.ts`.
 

src/esbuild/index.ts

@@ -14,35 +14,12 @@ import { externalPlugin } from './external'
 import { postcssPlugin } from './postcss'
 import { sveltePlugin } from './svelte'
 import consola from 'consola'
-import { truthy } from '../utils'
+import { defaultOutExtension, truthy } from '../utils'
 import { swcPlugin } from './swc'
 import { nativeNodeModulesPlugin } from './native-node-module'
 import { PluginContainer } from '../plugin'
 import { OutExtensionFactory } from '../options'
 
-const defaultOutExtension = ({
-  format,
-  pkgType,
-}: {
-  format: Format
-  pkgType?: string
-}): { js: string } => {
-  let jsExtension = '.js'
-  const isModule = pkgType === 'module'
-  if (isModule && format === 'cjs') {
-    jsExtension = '.cjs'
-  }
-  if (!isModule && format === 'esm') {
-    jsExtension = '.mjs'
-  }
-  if (format === 'iife') {
-    jsExtension = '.global.js'
-  }
-  return {
-    js: jsExtension,
-  }
-}
-
 const getOutputExtensionMap = (
   options: NormalizedOptions,
   format: Format,

src/index.ts

@@ -238,7 +238,7 @@ export async function build(_options: Options) {
                 // .d.ts files are removed in the `dtsTask` instead
                 // `dtsTask` is a separate process, which might start before `mainTasks`
                 if (options.dts) {
-                  extraPatterns.unshift('!**/*.d.ts')
+                  extraPatterns.unshift('!**/*.d.{ts,cts,mts}')
                 }
                 await removeFiles(['**/*', ...extraPatterns], options.outDir)
                 logger.info('CLI', 'Cleaning output folder')

src/options.ts

@@ -14,7 +14,7 @@ export type ContextForOutPathGeneration = {
   pkgType?: string
 }
 
-export type OutExtensionObject = { js?: string }
+export type OutExtensionObject = { js?: string, dts?: string }
 
 export type OutExtensionFactory = (
   ctx: ContextForOutPathGeneration

src/rollup.ts

@@ -5,10 +5,10 @@ import ts from 'typescript'
 import hashbangPlugin from 'rollup-plugin-hashbang'
 import jsonPlugin from '@rollup/plugin-json'
 import { handleError } from './errors'
-import { removeFiles } from './utils'
+import { defaultOutExtension, removeFiles } from './utils'
 import { TsResolveOptions, tsResolvePlugin } from './rollup/ts-resolve'
 import { createLogger, setSilent } from './log'
-import { getProductionDeps } from './load'
+import { getProductionDeps, loadPkg } from './load'
 import path from 'path'
 import { reportSize } from './lib/report-size'
 import resolveFrom from 'resolve-from'
@@ -32,7 +32,7 @@ const dtsPlugin: typeof import('rollup-plugin-dts') = require('rollup-plugin-dts
 
 type RollupConfig = {
   inputConfig: InputOptions
-  outputConfig: OutputOptions
+  outputConfig: OutputOptions[]
 }
 
 const findLowestCommonAncestor = (filepaths: string[]) => {
@@ -111,13 +111,14 @@ const getRollupConfig = async (
     }
   }
 
+  const pkg = await loadPkg(process.cwd())
   const deps = await getProductionDeps(process.cwd())
 
   const tsupCleanPlugin: Plugin = {
     name: 'tsup:clean',
     async buildStart() {
       if (options.clean) {
-        await removeFiles(['**/*.d.ts'], options.outDir)
+        await removeFiles(['**/*.d.{ts,mts,cts}'], options.outDir)
       }
     },
   }
@@ -188,13 +189,19 @@ const getRollupConfig = async (
         ...(options.external || []),
       ],
     },
-    outputConfig: {
-      dir: options.outDir || 'dist',
-      format: 'esm',
-      exports: 'named',
-      banner: dtsOptions.banner,
-      footer: dtsOptions.footer,
-    },
+    outputConfig: options.format.map((format) => {
+      const outputExtension =
+        options.outExtension?.({ format, options, pkgType: pkg.type }).dts ||
+        defaultOutExtension({ format, pkgType: pkg.type }).dts
+      return {
+        dir: options.outDir || 'dist',
+        format: 'esm',
+        exports: 'named',
+        banner: dtsOptions.banner,
+        footer: dtsOptions.footer,
+        entryFileNames: `[name]${outputExtension}`,
+      }
+    }),
   }
 }
 
@@ -207,15 +214,16 @@ async function runRollup(options: RollupConfig) {
     }
     logger.info('dts', 'Build start')
     const bundle = await rollup(options.inputConfig)
-    const result = await bundle.write(options.outputConfig)
+    const results = await Promise.all(options.outputConfig.map(bundle.write))
+    const outputs = results.flatMap((result) => result.output)
     logger.success('dts', `⚡️ Build success in ${getDuration()}`)
     reportSize(
       logger,
       'dts',
-      result.output.reduce((res, info) => {
+      outputs.reduce((res, info) => {
         const name = path.relative(
           process.cwd(),
-          path.join(options.outputConfig.dir || '.', info.fileName)
+          path.join(options.outputConfig[0].dir || '.', info.fileName)
         )
         return {
           ...res,
@@ -231,7 +239,7 @@ async function runRollup(options: RollupConfig) {
 
 async function watchRollup(options: {
   inputConfig: InputOptions
-  outputConfig: OutputOptions
+  outputConfig: OutputOptions[]
 }) {
   const { watch } = await import('rollup')
 

src/utils.ts

@@ -2,6 +2,7 @@ import fs from 'fs'
 import glob from 'globby'
 import resolveFrom from 'resolve-from'
 import strip from 'strip-json-comments'
+import { Format } from './options'
 
 export type MaybePromise<T> = T | Promise<T>
 
@@ -129,3 +130,30 @@ export function jsoncParse(data: string) {
     return {}
   }
 }
+
+export function defaultOutExtension({
+  format,
+  pkgType,
+}: {
+  format: Format
+  pkgType?: string
+}): { js: string, dts: string } {
+  let jsExtension = '.js'
+  let dtsExtension = '.d.ts'
+  const isModule = pkgType === 'module'
+  if (isModule && format === 'cjs') {
+    jsExtension = '.cjs'
+    dtsExtension = '.d.cts'
+  }
+  if (!isModule && format === 'esm') {
+    jsExtension = '.mjs'
+    dtsExtension = '.d.mts'
+  }
+  if (format === 'iife') {
+    jsExtension = '.global.js'
+  }
+  return {
+    js: jsExtension,
+    dts: dtsExtension,
+  }
+}

test/index.test.ts

@@ -1248,7 +1248,7 @@ test(`custom tsconfig should pass to dts plugin`, async () => {
         }
       `,
   })
-  expect(outFiles).toEqual(['input.d.ts'])
+  expect(outFiles).toEqual(['input.d.mts'])
 })
 
 test(`should generate export {} when there are no exports in source file`, async () => {
@@ -1268,8 +1268,8 @@ test(`should generate export {} when there are no exports in source file`, async
         }
       `,
   })
-  expect(outFiles).toEqual(['input.d.ts', 'input.mjs'])
-  expect(await getFileContent('dist/input.d.ts')).toContain('export { }')
+  expect(outFiles).toEqual(['input.d.mts', 'input.mjs'])
+  expect(await getFileContent('dist/input.d.mts')).toContain('export { }')
 })
 
 test('custom inject style function', async () => {
@@ -1335,3 +1335,32 @@ test('should load postcss esm config', async () => {
   expect(outFiles).toEqual(['input.cjs', 'input.css'])
   expect(await getFileContent('dist/input.css')).toContain('color: blue;')
 })
+
+test('should emit a declaration file per format', async () => {
+  const { outFiles } = await run(getTestName(), {
+    'input.ts': `export default 'foo'`,
+    'tsup.config.ts': `
+        export default {
+          entry: ['src/input.ts'],
+          format: ['esm', 'cjs'],
+          dts: true
+        }`,
+  });
+  expect(outFiles).toEqual(['input.d.mts', 'input.d.ts', 'input.js', 'input.mjs'])
+});
+
+test('should emit a declaration file per format (type: module)', async () => {
+  const { outFiles } = await run(getTestName(), {
+    'input.ts': `export default 'foo'`,
+    'package.json': `{
+      "type": "module"
+    }`,
+    'tsup.config.ts': `
+        export default {
+          entry: ['src/input.ts'],
+          format: ['esm', 'cjs'],
+          dts: true
+        }`,
+  });
+  expect(outFiles).toEqual(['input.cjs', 'input.d.cts', 'input.d.ts', 'input.js'])
+});