experimental: Using preact-iso to lazy load components

[rschristian]

What kind of change does this PR introduce?

Experimental refactor

Did you add tests for your changes?

Yes

Summary

Deprecates async-loader and automatic route splitting for instead relying on lazy loading, like with preact-iso's lazy().

Code splitting as it previously worked was quite opaque, relying on magic directory names rather than user code.

This should make bundle splitting much more transparent by moving the control into user code.

// before
import Home from './routes/home';

// after
const Home = lazy(() => import('./routes/home.js'));

Does this PR introduce a breaking change?

Yes

[changeset-bot]

🦋 Changeset detected

Latest commit: 076d599

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
preact-cli	Major

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[rschristian]

Webpack is not able to provide names for chunks created with import(). This has two major implications:

1. We'll need to create names else we'll see things like 611.chunk.js in the output
2. Named chunk groups will not work at all. We currently use them to build the push manifest.

So, I elected to solve this with a Babel plugin. It simply inserts a magic comment to specify the chunk name based upon the import path (import('./routes/foo.js') -> import(/* webpackChunkName: "routes-foo" */ "./routes-foo.js")). Source

The advantage of this approach is that users will not have to manually annotate their imports, we will not have to switch chunks to have named IDs¹, we get file names that closely resemble previous output, and we keep named chunk groups.

Hopefully it's not an issue adding my own module. It's quite simple and I'm happy to maintain it if there are any issues.

---

1. We could set Webpack to create chunks with names for IDs and extrapolate file names from there, but that hurts perf and still won't give names to the chunk groups.

[rschristian]

Note to self: 20kb jump seems quite heavy. Thinking something isn't right.