Background

A few independent incidences

After updating rollup to 3.22.0, the package embroider-css-modules worked, in the sense that the consuming app (a test app) continued to run and all tests for the test app continued to pass. I noticed, however, that the lint:types script of the test app failed because embroider-css-modules didn't create dist/index.d.ts in the same way as before.

app/components/widgets/widget-4/memo/actions.gts:3:28 - error TS2306: File '/packages/embroider-css-modules/dist/index.d.ts' is not a module.

3 import { localClass } from 'embroider-css-modules';
                             ~~~~~~~~~~~~~~~~~~~~~~~

app/components/ui/form/field.gts:4:28 - error TS2306: File '/packages/embroider-css-modules/dist/index.d.ts' is not a module.

4 import { localClass } from 'embroider-css-modules';

What dist looked like before updating rollup

What dist looked like after updating rollup

After updating rollup to 3.22.0 in another package (in another repo), I noticed that a different file called dist/template-registry.d.ts had been created differently. The test app for that package also failed lint:types as a result.

import UiSpinnerComponent from "./components/ui/spinner.js";
interface UiSpinnerRegistry {
    'Ui::Spinner': typeof UiSpinnerComponent;
}
export { UiSpinnerRegistry as default };

export {};

Finally, on Discord, @jeffsawatzky described encountering a similar issue.

And it [Glint] is mostly working, except that the registry that I define in template-registry.ts don't get saved in template-registry.d.ts after build. Instead that file is blank, and the code I put in template-registry.ts ends up in index.d.ts. I've looked at other examples, but I haven't been able to figure this out.

Possible root cause

I reported the issue to the maintainers of rollup in rollup/rollup#5008.

@lukastaegert noticed, the problem seemed to be limited to *.d.ts files, e.g. dist/index.d.ts, dist/template-registry.d.ts. If so, rollup-plugin-ts (which we use to support TypeScript) or one of its dependencies, might have made an assumption about chunks that is not valid as of [email protected].

Proposed solution

Lukas (who maintains rollup) and I both think, a good option is for @embroider/addon-dev to explicitly set output.experimentalMinChunkSize to 0.

Maybe explicitly setting output.experimentalMinChunkSize:0 in the shared config is not a bad idea for now. The reasoning for setting it to 1 was that there should not be adverse effects to users, but it should avoid some empty chunks. It would still be helpful if someone with more knowledge about the workings of rollup-plugin-dts could look into this and determine if the empty files are a bug in the plugin or in Rollup. In the worst case, we could change the default back to 0 until the next major version.

This way, an addon maintainer doesn't need to set the value themselves in rollup.config.js:

/* rollup.config.{js,mjs} */

import { Addon } from '@embroider/addon-dev/rollup';
import typescript from 'rollup-plugin-ts';

const addon = new Addon({
  srcDir: 'src',
  destDir: 'dist',
});

export default {
  output: {
    ...addon.output(),
    experimentalMinChunkSize: 0,  // <-- Current workaround for addon developers
  },

  plugins: [ ... ],
};

At the same time, the maintainers of rollup could continue to iterate on the default value of experimentalMinChunkSize for v3 and v4.

Related links

• Updated @embroider packages ijlee2/embroider-css-modules#42 (comment)
• https://rollupjs.org/configuration-options/#output-experimentalminchunksize
• Rollup 3.22.0 and higher chunkFileNames (*.js) filename bug rollup/rollup#5008