fix: push manifest

[rschristian]

What kind of change does this PR introduce?

Bug fix / refactoring for future use

Did you add tests for your changes?

Yes

Summary

Closes #1675

In short, the push-manifest.json output had hard-coded expectations that caused two problems in the linked issue:

• If the asset could not be found, there would be an "undefined" entry in the push-manifest
• If the asset output paths were altered, they could not be added to the manifest due to the strict filename matching

This fixes both issues by using webpack-manifest-plugin (Webpack really should make this part of core, extremely useful to expose this info to other plugins).

This plugin provides a map output assets that allows us to keep our expectation about a bundle.css or route-home.js existing, but allows users to still customize the actual output. For example, the following config:

// preact.config.js
export default (config, env, helpers) => {
	config.output.publicPath = '/foo/';

	const { plugin: miniCssExtractPlugin } = helpers.getPluginsByName(config, "MiniCssExtractPlugin")[0];
	miniCssExtractPlugin.options.filename = "styles/foobar.css";
};

...would create the following manifest:

{
  "/bundle.css": "/foo/styles/foobar.css",
  "/bundle.js": "/foo/bundle.29bec.esm.js",
  "/bundle.js.map": "/foo/bundle.29bec.esm.js.map",
}

Should allow users to customize output names as they wish without it interfering with any assumptions we've made about output.

In the future we might be able to make greater use of this and move away from asset path concatenation like the following:

preact-cli/packages/cli/lib/resources/head-end.ejs

Line 1 in a56d904

<link rel="manifest" href="<%= htmlWebpackPlugin.files.publicPath %>manifest.json">

However, for now, I'd hesitate to do that as this might break some configs. Better to wait for a major.

Still, it should allow for much more robust targeting of output assets as it won't fall to pieces if a user makes configuration changes.

Does this PR introduce a breaking change?

No

[changeset-bot]

🦋 Changeset detected

Latest commit: 86338c6

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	Patch

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[rschristian]

In case this raises an eyebrow, the asset manifest will always map to ESM output if enabled, CJS if it's not. We don't need to deal with that ourselves anymore.

There's a new test to ensure the push-manifest.json is correct and referring to ESM scripts when ESM is enabled.