feat: a defineConfig API from @vue/cli-service for better typing support in vue.config.js (#6355)

Author: haoqunjiang

docs/config/README.md

@@ -27,6 +27,17 @@ module.exports = {
 }
 ```
 
+Or, you can use the `defineConfig` helper from `@vue/cli-service`, which could provide better intellisense support:
+
+```js
+// vue.config.js
+const { defineConfig } = require('@vue/cli-service')
+
+module.exports = defineConfig({
+  // options...
+})
+```
+
 ### baseUrl
 
 Deprecated since Vue CLI 3.3, please use [`publicPath`](#publicPath) instead.

docs/zh/config/README.md

@@ -26,6 +26,18 @@ module.exports = {
   // 选项...
 }
 ```
+
+或者，你也可以使用 `@vue/cli-service` 提供的 `defineConfig` 帮手函数，以获得更好的类型提示：
+
+```js
+// vue.config.js
+const { defineConfig } = require('@vue/cli-service')
+
+module.exports = defineConfig({
+  // 选项
+})
+```
+
 ### baseUrl
 
 从 Vue CLI 3.3 起已弃用，请使用[`publicPath`](#publicpath)。

packages/@vue/cli-service/lib/Service.js

@@ -436,3 +436,6 @@ function cloneRuleNames (to, from) {
     }
   })
 }
+
+/** @type {import('../types/index').defineConfig} */
+module.exports.defineConfig = (config) => config

packages/@vue/cli-service/types/index.d.ts

@@ -3,7 +3,7 @@ import ChainableConfig = require('webpack-chain')
 import webpack = require('webpack')
 import WebpackDevServer = require('webpack-dev-server')
 import express = require('express') // @types/webpack-dev-server depends on @types/express
-import { ProjectOptions } from './ProjectOptions'
+import { ProjectOptions, ConfigFunction } from './ProjectOptions'
 
 type RegisterCommandFn = (args: minimist.ParsedArgs, rawArgv: string[]) => any
 
@@ -134,4 +134,5 @@ type ServicePlugin = (
 ) => any
 
 export { ProjectOptions, ServicePlugin, PluginAPI }
-export { ConfigFunction } from './ProjectOptions'
+type UserConfig = ProjectOptions | ConfigFunction
+export function defineConfig(config: UserConfig): UserConfig