Declaration source maps are broken

[mrazauskas]

Checklist

• [x] I can reproduce this issue when running this plugin on its own. Other plugins, such as node-resolve are known to cause issues.
• [x] I am running this plugin on .d.ts files generated by TypeScript. The plugin can consume .ts and even .js files (with allowJs: true), but this is known to cause issues.
• [x] This issue is not related to rolling up @types. The plugin ignores these by default, unless respectExternal is set. @types can contain hand-crafted code which is known to cause issues.

Code Snipped

export function sum(a: string, b: string) {
  return a + b;
}

Repro

To make life easier, I have created reproduction repo: https://github.com/mrazauskas/x-rollup-declaration-map

Please clone it and follow these steps to reproduce the issue:

1. Run yarn to install dependencies.
2. Run yarn build --declarationMap. It will use tsc directly, the resulting declaration file and its source map can be found in the ./build directory.
3. Run yarn bundle --sourcemap. It will use Rollup together with the rollup-plugin-dts, the resulting declaration file and its source map can be found in the ./bundle directory. sourceMappingURL is included in the index.d.ts file, but unfortunately the index.d.ts.map is broken.

I would expect to have working index.d.ts.map in the ./bundle directory. Why not? Rollup has great support for source maps.

[Swatinem]

Declaration SourceMaps are generally not supported. Feature development has also halted on this project, see #277

[mrazauskas]

Thanks. This is your project. Just wanted to draw attention.

[llllvvuu]

@mrazauskas could you share the repo again? I am considering to try making a fork with this feature

[mrazauskas]

I don't have it any more, but it was rather simple project with two ts. Building it with tsc was emitting the mapping for .d.ts. But building it with Rollup with --sourcemap flag was emitting empty/broken mapping.