Check before registering @fastify/middie (#355)

Author: onlywei

.changeset/jolly-roses-write.md

@@ -0,0 +1,5 @@
+---
+"@fastify/vite": patch
+---
+
+Check decorators before registering `@fastify/middie` internally. This should allow middie to be registered separately if users want to configure specific options.

docs/guide/known-limitations.md

@@ -1,9 +1,33 @@
 # Known Limitations
 
-- It's currently impossible to run **`@fastify/vite`** in an encapsulated Fastify plugin. You'll need to register **`@fastify/vite`** at the root context, or if you want to use it in a plugin, that plugin must be wrapped in [`fastify-plugin`](https://github.com/fastify/fastify-plugin) so it's also registered at the root context.
+## Encapsulated Plugin Registration
 
-  > Investigation on this has started but is still pending — everything points to **`@fastify/middie`**, the Express compatibility layer needed to run the Vite development server middleware. It's just considered low-prio at the moment as in most setups, only a single instance is needed anyway.
+It's currently impossible to run `@fastify/vite` in an encapsulated Fastify plugin. You'll need to register `@fastify/vite` at the root context, or if you want to use it in a plugin, that plugin must be wrapped in [`fastify-plugin`](https://github.com/fastify/fastify-plugin) so it's also registered at the root context.
 
-- It's currently impossible to run **multiple** Vite development server middleware in your Fastify server, which means `@fastify/vite` can **only be registered once**. Configuration for this is somewhat tricky and there isn't documentation on how to do it. Once [#108](https://github.com/fastify/fastify-vite/pull/108) is completed and merged, it will open the path to have a Vite development server factory that can create instances on-demand, but that approach still remains to be tested.
+::: info
+Investigation on this has started but is still pending — everything points to `@fastify/middie`, the Express compatibility layer needed to run the Vite development server middleware. It's just considered low-prio at the moment as in most setups, only a single instance is needed anyway.
+:::
 
-  If you're looking into a microfrontend setup, consider [this approach](https://dev.to/getjv/react-micro-frontends-with-vite-5442).
+## Multiple Vite Instances
+
+It's currently impossible to run **multiple** Vite development server middleware in your Fastify server, which means `@fastify/vite` can **only be registered once**. Configuration for this is somewhat tricky and there isn't documentation on how to do it. Once [#108](https://github.com/fastify/fastify-vite/pull/108) is completed and merged, it will open the path to have a Vite development server factory that can create instances on-demand, but that approach still remains to be tested.
+
+If you're looking into a microfrontend setup, consider [this approach](https://dev.to/getjv/react-micro-frontends-with-vite-5442).
+
+## Using @fastify/middie Directly
+
+`@fastify/vite` internally registers `@fastify/middie` to run Vite's development server middleware. If you need to register `@fastify/middie` yourself (e.g., to pass custom options), register it **before** `@fastify/vite`:
+
+```js
+import Fastify from 'fastify'
+import middie from '@fastify/middie'
+import FastifyVite from '@fastify/vite'
+
+const server = Fastify()
+
+// Register middie first with your options
+await server.register(middie, { /* your options */ })
+await server.register(FastifyVite, { /* options */ })
+```
+
+`@fastify/vite` checks if middie is already registered and skips its own registration if so.

packages/fastify-vite/mode/development.js

@@ -46,8 +46,10 @@ async function setup(config) {
   const { createServer, createServerModuleRunner, mergeConfig, defineConfig } = await import('vite')
 
   // Middie seems to work well for running Vite's development server
-  // Unsure if fastify-express is warranted here
-  await this.scope.register(middie)
+  // Check if middie is already registered (allows users to register it themselves)
+  if (!this.scope.hasDecorator('use')) {
+    await this.scope.register(middie)
+  }
 
   // Create and enable Vite's Dev Server middleware
   const devServerOptions = mergeConfig(