docs(chunkSplitting): add manualChunks object form syntax warning w…

…hen it is used with the `splitVendorChunk` plugin (#13431)

Co-authored-by: patak <matias.capeletto@gmail.com>

docs/guide/build.md

@@ -60,6 +60,10 @@ export default defineConfig({
 
 This strategy is also provided as a `splitVendorChunk({ cache: SplitVendorChunkCache })` factory, in case composition with custom logic is needed. `cache.reset()` needs to be called at `buildStart` for build watch mode to work correctly in this case.
 
+::: warning
+You should use `build.rollupOptions.output.manualChunks` function form when using this plugin. If the object form is used, the plugin won't have any effect.
+:::
+
 ## Rebuild on files changes
 
 You can enable rollup watcher with `vite build --watch`. Or, you can directly adjust the underlying [`WatcherOptions`](https://rollupjs.org/configuration-options/#watch) via `build.watch`:

packages/vite/src/node/plugins/splitVendorChunk.ts

@@ -116,6 +116,10 @@ export function splitVendorChunkPlugin(): Plugin {
               }
               // else, leave the object form of manualChunks untouched, as
               // we can't safely replicate rollup handling.
+              // eslint-disable-next-line no-console
+              console.warn(
+                "(!) the `splitVendorChunk` plugin doesn't have any effect when using the object form of `build.rollupOptions.manualChunks`. Consider using the function form instead.",
+              )
             } else {
               output.manualChunks = viteManualChunks
             }