[RFC] Shared Bundle

[huozhi]

Background

shared-runtime modules is not ideal for shared chunks spltting as it's fully based on code splitting strategy, when you import different exports from a shared module, they could be split into different chunks instead of being grouped into a same output bundle, event they're in the same group of split chunks.

Thus we need to have an entry as input for a shared module, and then alias it like the other chunks. Since now we have the relative exports in #538 , so we could auto generate shared entries based on the #imports field to create shared links.

Proposal

We still want to follow a certain pattern that we could only select few aliases as shared module inputs, then bunchee will only generate the shared entries and output for these entry files. The rest of the alias will just be normal aliases.

Use #[name].shared as the pattern to match all the shared bundles

{
  "imports": {
    "#polyfill": "./src/polyfill.js",
    "#dep.shared": "./src/dep.shared.js"
  }
}

Then bunchee should create a bundle for #dep.shared, where input file is ./src/dep.shared.js. And the rest follows the rules of normal entries. This could improve the shared modules story and without adding much new convention or patterns to memorize