From 36fabe73adb04d15d2b03fb805d6959ab7ef8fd4 Mon Sep 17 00:00:00 2001
From: Etienne Gobeli <gobeli@puzzle.ch>
Date: Mon, 14 Jun 2021 08:35:45 +0200
Subject: [PATCH] feat(vite): update LibraryOptions and add docs

---
 docs/config/index.md            | 4 ++--
 packages/vite/src/node/build.ts | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/docs/config/index.md b/docs/config/index.md
index 6c6370fb0c8dbf..d65c49dd6567d9 100644
--- a/docs/config/index.md
+++ b/docs/config/index.md
@@ -602,10 +602,10 @@ createServer()
 
 ### build.lib
 
-- **Type:** `{ entry: string, name?: string, formats?: ('es' | 'cjs' | 'umd' | 'iife')[], fileName?: string }`
+- **Type:** `{ entry: string, name?: string, formats?: ('es' | 'cjs' | 'umd' | 'iife')[], fileName?: string | ((format: ModuleFormat) => string) }`
 - **Related:** [Library Mode](/guide/build#library-mode)
 
-  Build as a library. `entry` is required since the library cannot use HTML as entry. `name` is the exposed global variable and is required when `formats` includes `'umd'` or `'iife'`. Default `formats` are `['es', 'umd']`. `fileName` is the name of the package file output, default `fileName` is the name option of package.json
+  Build as a library. `entry` is required since the library cannot use HTML as entry. `name` is the exposed global variable and is required when `formats` includes `'umd'` or `'iife'`. Default `formats` are `['es', 'umd']`. `fileName` is the name of the package file output, default `fileName` is the name option of package.json, it can also be defined as function taking the `format` as an argument.
 
 ### build.manifest
 
diff --git a/packages/vite/src/node/build.ts b/packages/vite/src/node/build.ts
index 372f636b363359..120cb4a87445ab 100644
--- a/packages/vite/src/node/build.ts
+++ b/packages/vite/src/node/build.ts
@@ -193,7 +193,7 @@ export interface LibraryOptions {
   entry: string
   name?: string
   formats?: LibraryFormats[]
-  fileName?: string | ((format?: ModuleFormat) => string)
+  fileName?: string | ((format: ModuleFormat) => string)
 }
 
 export type LibraryFormats = 'es' | 'cjs' | 'umd' | 'iife'
@@ -619,7 +619,7 @@ export function resolveLibFilename(
   format: ModuleFormat | undefined,
   pkgName: string
 ): string {
-  return typeof libOptions.fileName === 'function'
+  return typeof libOptions.fileName === 'function' && format
     ? libOptions.fileName(format)
     : `${libOptions.fileName || pkgName}.${format || `es`}.js`
 }