rollup 4.63.0 tree-shaking regression: rxjs side-effect modules dropped, awaited promise never settles

README.md

rollup 4.63.0 regression: side-effectful rxjs modules tree-shaken away

Minimal reproduction for a tree-shaking regression introduced in rollup 4.63.0.

Run

npm install   # package.json pins rollup 4.63.0 via overrides
npx vite build
node dist/index.js

With "overrides": {"rollup": "4.63.0"} (as committed): the awaited lastValueFrom(...) promise never settles — node prints "Warning: Detected unsettled top-level await" and exits with code 13.

Change the override to "rollup": "4.62.5", reinstall, rebuild: prints RESULT: 2 and exits 0.

What gets dropped

Diffing the sourcemap sources between the two builds, 4.63.0 removes these side-effectful rxjs-internal modules that 4.62.5 keeps:

• rxjs/dist/cjs/internal/util/errorContext.js
• rxjs/dist/cjs/internal/NotificationFactories.js
• rxjs/dist/cjs/internal/scheduler/timeoutProvider.js

Reproduces with build.minify: false as well, so esbuild minification is not involved. rxjs is consumed through @rollup/plugin-commonjs (the cjsExports wrapper) via vite's default pipeline.

entry.js

import { of, lastValueFrom } from 'rxjs';
import { map } from 'rxjs/operators';

const value = await lastValueFrom(of(1).pipe(map((x) => x + 1)));
console.log('RESULT:', value);

package.json

{
  "name": "rollup-4630-rxjs-repro",
  "private": true,
  "type": "module",
  "dependencies": {
    "rxjs": "^7.8.2",
    "vite": "^7.3.0"
  },
  "overrides": {
    "rollup": "4.63.0"
  }
}

vite.config.js

import { defineConfig } from 'vite';
export default defineConfig({
  resolve: { conditions: ['module', 'node'], mainFields: ['module'] },
  esbuild: { keepNames: true },
  build: {
    minify: false,
    sourcemap: true,
    lib: { entry: { index: './entry.js' }, formats: ['es'] },
    rollupOptions: { external: [] },
  },
});