Treeshake dynamic import of modules

[jakearchibald]

Feature Use Case

Rollup now treeshakes dynamically imported modules in a lot of cases, which is brilliant, but there are a couple of important cases where it de-opts:

maths.js

export const square = x => x * x;
export const double = x => x * 2;

These cases will not treeshake:

const module = await import('./maths.js');
module.square(4);

Demo

const square = await import('./maths.js').then((m) => m.square);
square(4);

Demo

This is unexpected, because the static equivalent treeshakes.

Feature Proposal

Treeshake pls 😄