Newer `terser` breaks the production build

[jtpio]

After updating dependencies in https://github.com/jupyterlite/pyodide-kernel/pull/226, starting a new kernel using a production of jupyterlite-pyodide-kernel fails with:

Failed to construct 'Worker': Failed to read the 'type' property from 'WorkerOptions':
Cannot convert object to primitive value

In packages/pyodide-kernel/src/kernel.ts, workers are created with:

new Worker(new URL('./comlink.worker.js', import.meta.url), {
  type: 'module',
})

Looking more closely at the built assets:

Dev:

new Worker(new URL(...), {
  type: undefined,
})

Prod (minified):

new Worker(new URL(...), {
  type: s,  // Variable reused - 's' is the pypi import namespace object
})

This seems to be caused by a new version of terser, which likely introduced more aggressive variable reuse optimizations.

The UI tests didn't catch this because they were using the dev build, where the issue doesn't manifest.

[jtpio]

https://github.com/jupyterlite/pyodide-kernel/pull/231 confirmed the issue with the prod build and reverted the terser update for now.

We should look into a proper fix compatible with newer versions of terser and webpack.

[jtpio]

We should look into a proper fix compatible with newer versions of terser and webpack.

Adding the following to https://github.com/jupyterlite/pyodide-kernel/blob/main/packages/pyodide-kernel-extension/webpack.config.js will likely help:

experiments: {
  outputModule: true,
},