fix: better handling of resync and restarts in content layer

[ascorbic]

Changes

This PR makes a number of changes to the way that file watchers work in dev with the content layer. There have been a few bugs related to the way that dev server restarts are handled, which were due to the way we were handling file watchers.

When the Astro config is edited, it restarts the dev container to ensure the site is using the latest config. This was causing several bugs:

• when the server was restarted, it wasn't re-running the Astro sync. This meant that updates in the config were not reflected in the rendered config, for example changes to Markdown config wouldn't update the rendered content.
• the existing watcher was destroyed, but because the loaders weren't being re-run, the glob and file event listeners weren't being attached to the new watcher.

This PR correctly passes in the watcher, but has to handle various implications of this:

• it needs to ensure that the content layer is recreated when the server is restarted, otherwise it will use the old config even when it syncs the content. This fixes Shiki Theme Changes Not Reflected in Content Collection #12700
• it needs to detach the event listeners that the previous loader run added. We can't clear them all, because this is a shared watcher instance. To handle this, we now wrap the watcher with a Proxy that keeps track of which listeners were attached by the content layer, so they can be removed if the content layer is refreshed or disposed of. Fixes content collections stop updating in dev server after restarting for Astro config updates #12976
• it needs to ensure that the files themselves are still being watched, so it now manually adds them to the watcher rather than relying on them still being watched

Testing

Added new test cases

Docs

[changeset-bot]

🦋 Changeset detected

Latest commit: 8452a0d

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[codspeed-hq]

CodSpeed Performance Report

Merging #12984 will not alter performance

_{Comparing watch-after-reload (8452a0d) with main (1a026af)}

Summary

✅ 6 untouched benchmarks

[florian-lefebvre]

Isn't a proxy overkill for this? Could it be an object?

return {
	on: (event, callback) => {
				 if (!listeners.has(event)) {
						listeners.set(event, new Set());
					}

					// Track the listener
					listeners.get(event)!.add(callback);

				return watcher.on(event, callback)
	},
	// off, etc
}

Or is it because you want to support all other methods too?

[ascorbic]

Yeah, it's a public API, so it would be a breaking change if I changed the type.