This patch brings hot reloading capabilities to PHP apps: in
development, the browser will automatically refresh the page when any
source file changes!
It's similar to HMR in JavaScript.
It is built on top of [the watcher
mechanism](https://frankenphp.dev/docs/config/#watching-for-file-changes)
and of the [Mercure](https://frankenphp.dev/docs/mercure/) integration.
Each time a watched file is modified, a Mercure update is sent, giving
the ability to the client to reload the page, or part of the page
(assets, images...).
Here is an example implementation:
```caddyfile
root ./public
mercure {
subscriber_jwt {env.MERCURE_SUBSCRIBER_JWT_KEY}
anonymous
}
php_server {
hot_reload
}
```
```php
<?php
header('Content-Type: text/html');
?>
<!DOCTYPE html>
<html lang="en">
<head>
<title>Test</title>
<script>
const es = new EventSource('<?=$_SERVER['FRANKENPHP_HOT_RELOAD']?>');
es.onmessage = () => location.reload();
</script>
</head>
<body>
Hello
```
I plan to create a helper JS library to handle more advanced cases
(reloading CSS, JS, etc), similar to [HotWire
Spark](https://github.com/hotwired/spark). Be sure to attend my
SymfonyCon to learn more!
There is still room for improvement:
- Provide an option to only trigger the update without reloading the
worker for some files (ex, images, JS, CSS...)
- Support classic mode (currently, only the worker mode is supported)
- Don't reload all workers when only the files used by one change
However, this PR is working as-is and can be merged as a first step.
This patch heavily refactors the watcher module. Maybe it will be
possible to extract it as a standalone library at some point (would be
useful to add a similar feature but not tight to PHP as a Caddy module).
---------
Signed-off-by: Kévin Dunglas <kevin@dunglas.fr>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
