# rollup-plugin-dts

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This is a plugin that lets you roll-up your `.d.ts` definition files.

## Usage

Install the package from `npm`:

    $ npm install --save-dev rollup-plugin-dts

Add it to your `rollup.config.js`:

```js
import { dts } from "rollup-plugin-dts";

const config = [
  // …
  {
    input: "./my-input/index.d.ts",
    output: [{ file: "dist/my-library.d.ts", format: "es" }],
    plugins: [dts()],
  },
];

export default config;
```

**NOTE** A [default import](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#default_import) of the plugin using `import dts from "rollup-plugin-dts";` is still supported for existing implementations of this package. However, a [named import](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#named_import) is suggested to avoid the error `[!] TypeError: dts is not a function`[^1][^2] in certain rollup config file implementations.

And then instruct typescript where to find your definitions inside your `package.json`:

```json
  "types": "dist/my-library.d.ts",
```

**NOTE** that the plugin will automatically mark any external library
(`@types` for example) as `external`, so those will be excluded from bundling.

## Options

```js
plugins: [dts({
  // Enable detailed sourcemaps for Go-to-Definition support.
  // When true: loads .d.ts.map files and captures TypeScript's declarationMap
  // for .ts inputs, enabling navigation to original source files.
  // NOTE: Also requires `output.sourcemap: true` in your Rollup config.
  sourcemap: true,

  // Path to tsconfig.json (default: finds nearest tsconfig.json)
  tsconfig: "./tsconfig.json",

  // TypeScript compiler options (e.g., for path mapping)
  compilerOptions: { baseUrl: ".", paths: { "~/*": ["src/*"] } },

  // Don't auto-externalize node_modules (default: false)
  respectExternal: true,

  // Bundle types from specific external packages (default: [])
  includeExternal: ["some-package"],
})]
```

## TypeScript 7 support

TypeScript 7.0 (the native compiler) does not ship a compiler API, which this
plugin relies on. When your project uses `typescript@7`, additionally install
the official compatibility package that provides the TypeScript 6 API:

    $ npm install --save-dev @typescript/typescript6

The plugin uses the API from your `typescript` package when it provides one
(TypeScript 4.5 – 6.x), and automatically falls back to
`@typescript/typescript6` otherwise. Declaration files are parsed and emitted
with the TypeScript 6 language behavior in that case, which is identical for
declaration output. Once TypeScript 7.1+ ships its new compiler API, a future
release will support it directly.

Note that this plugin's public types reference the `typescript` package (e.g.,
`ts.CompilerOptions`), which `typescript@7` does not currently provide. If you
type-check a file that imports `rollup-plugin-dts` (such as `rollup.config.ts`)
with TypeScript 7, enable [`skipLibCheck`](https://www.typescriptlang.org/tsconfig/#skipLibCheck)
to avoid a spurious error inside the plugin's declaration file.

## Maintenance Mode

This project is in _maintenance mode_. That means there will be no more active feature development.
There will still be occasional releases to maintain compatibility with future TypeScript releases.
Pull Requests are always welcome, however reaction time on both Issues and PRs can be slow.

## What to expect

While this plugin is fairly complete, it does not support all imaginable use-cases.
In particular, the plugin works best with already existing `.d.ts` files generated
by the typescript compiler from idiomatic code.

Working with `.ts(x)` or even `.js(x)` (when setting `allowJs: true`) does work,
but is not recommended.

The plugin does its own import resolution through the typescript compiler, and
usage together with other resolution plugins, such as `node-resolve` can lead
to errors and is not recommended.

All external dependencies from `node_modules` are automatically excluded from
bundling. This can be overridden using the `respectExternal` setting, but it is
generally not recommended. While rollup of external `@types` generally works,
it is not recommended.

### TS2742 and shared declaration chunks

When a bundled entry exposes a type that originally came from a private shared
chunk, downstream `tsc --declaration` runs can fail with `TS2742`.

This is part of a broader TypeScript declaration portability problem. For
upstream context, see
[`./*.d.ts` required in `exports` to avoid `...not portable...`](https://github.com/microsoft/TypeScript/issues/60913)
for one shape of the bug, and
[`Elaborate on non-portable types`](https://github.com/microsoft/TypeScript/issues/53764)
for the related error-message discussion.

This plugin will try to rewrite that path through an entry that already
re-exports the type publicly. That keeps the existing public API and can make
the bundled declarations portable for downstream consumers.

The plugin does **not** invent new public exports. If no public entry re-exports
the shared type, the bundled package can still trigger `TS2742`. In that case,
the plugin emits a warning and the package should re-export the type from a
public entry explicitly.

## Why?

Well, ideally TypeScript should just do all this itself, and it even has a
[proposal](https://github.com/Microsoft/TypeScript/issues/4433) to do that.
But there hasn’t been any progress in ~3 years.

Some projects, like [rollup itself](https://github.com/rollup/rollup/blob/24fe07f39da8e4225f4bc4f797331930d8405ec2/src/rollup/types.d.ts)
go the route of completely separating their public interfaces in a separate file.

## Alternatives

- [API Extractor](https://api-extractor.com/)
- [dts-bundle-generator](https://github.com/timocov/dts-bundle-generator)
- [rollup-plugin-ts](https://github.com/wessberg/rollup-plugin-ts)
- [tsc-prog](https://github.com/jeremyben/tsc-prog)

[See](https://github.com/Swatinem/rollup-plugin-dts/issues/5)
[some](https://github.com/Swatinem/rollup-plugin-dts/issues/13)
[discussions](https://github.com/timocov/dts-bundle-generator/issues/68)
about some of these projects and their tradeoffs.

## [How does it work](./docs/how-it-works.md)

## License

The code is licensed under the copyleft **LGPL-3.0**. I have no intention to
license this under any non-copyleft license.

[^1]: [StackOverflow thread](https://stackoverflow.com/questions/74255565/rollup-typescript-error-dts-is-not-a-function/74304876#74304876) of issue
[^2]: [Github issue](https://github.com/Swatinem/rollup-plugin-dts/issues/247)
