It it possible to use plugin-typescript for generating d.ts exclusively?

[StreetStrider]

I compile my TS code with sucrase and I want to also generate d.ts for my files. It works out that @rollup/plugin-typescript is able to correctly generate typings for me. However, it intervenes in code compiling and I don't want it to. Besides doing double work here, compiling code two times, there is another reason. Sucrase does not change code formatting which is important for me, while plugin-typescript does.

Is there any way to completely prevent it from touching any generated code, while still generating typings?

[potatohoney-p]

Yes. Use noForceEmit: true together with TypeScript's declaration: true and emitDeclarationOnly: true, then let Sucrase handle the JavaScript transform:

import typescript from '@rollup/plugin-typescript';
import sucrase from '@rollup/plugin-sucrase';

export default {
  input: 'src/index.ts',
  output: { dir: 'dist', format: 'es' },
  plugins: [
    typescript({ tsconfig: './tsconfig.json', noForceEmit: true }),
    sucrase({ transforms: ['typescript'] }),
  ],
};

{
  "compilerOptions": {
    "target": "ESNext",
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "strict": true,
    "declaration": true,
    "emitDeclarationOnly": true,
    "declarationDir": "dist/types",
    "rootDir": "src"
  },
  "include": ["src/**/*.ts"]
}

The important part is noForceEmit: by default, the plugin overrides emitDeclarationOnly so that it can feed JavaScript to Rollup. With noForceEmit: true, it respects the declaration-only setting. Don't also set noEmit: true, since you still want declarations emitted.

I checked this with plugin-typescript 12.3.1, plugin-sucrase 5.1.0, TypeScript 5.9.3, and Rollup 4.60.0. A capture plugin immediately before Sucrase saw the original .ts source byte-for-byte; the final JavaScript matched a Sucrase-only build byte-for-byte, while types/index.d.ts was also generated. Removing noForceEmit: true changed the code reaching Sucrase and the final JavaScript in that fixture.

That keeps TypeScript out of JavaScript emission, but it still performs type analysis for the declarations, and Rollup itself can alter final bundle formatting. The byte-for-byte comparison above is against a Sucrase-only Rollup build, not a promise that the bundle preserves the original source layout in every case. I tested a non-watch build.

[StreetStrider]

Thanks for the help. For the time, I ended up using a simple parallel routine that uses tsc + noEmit + declaration + emitDeclarationOnly and it worked. Not as precise as visiting files with the Rollup plugin, but works.

I think I will check noForceEmit whenever I re-iterate this part of my setup. 🤝 Back then I've tried rollup-plugin-dts, rollup-plugin-ts, rollup-plugin-typescript2, @rollup/plugin-typescript and each one had some limitations I was not fond of.