refactor: use dotenv to parse env file and add a link to its docs (#3462)

Author: haoqunjiang

docs/guide/mode-and-env.md

@@ -16,6 +16,8 @@ FOO=bar
 VUE_APP_SECRET=secret
 ```
 
+For more detailed env parsing rules, please refer to [the documentation of `dotenv`](https://github.com/motdotla/dotenv#rules).
+
 Loaded variables will become available to all `vue-cli-service` commands, plugins and dependencies.
 
 ::: tip Env Loading Priorities

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

@@ -6,7 +6,7 @@ const readPkg = require('read-pkg')
 const merge = require('webpack-merge')
 const Config = require('webpack-chain')
 const PluginAPI = require('./PluginAPI')
-const loadEnv = require('./util/loadEnv')
+const dotenv = require('dotenv')
 const defaultsDeep = require('lodash.defaultsdeep')
 const { warn, error, isPlugin, loadModule } = require('@vue/cli-shared-utils')
 
@@ -95,7 +95,7 @@ module.exports = class Service {
 
     const load = path => {
       try {
-        const res = loadEnv(path)
+        const res = dotenv.config({ path, debug: process.env.DEBUG })
         logger(path, res)
       } catch (err) {
         // only ignore error if file is not found

packages/@vue/cli-service/lib/util/loadEnv.js

@@ -43,6 +43,7 @@
     "css-loader": "^1.0.1",
     "cssnano": "^4.1.8",
     "debug": "^4.1.1",
+    "dotenv": "^6.2.0",
     "escape-string-regexp": "^1.0.5",
     "file-loader": "^3.0.1",
     "fs-extra": "^7.0.1",

packages/@vue/cli-service/package.json

@@ -6059,6 +6059,11 @@ dot-prop@^4.1.0, dot-prop@^4.1.1, dot-prop@^4.2.0:
   dependencies:
     is-obj "^1.0.0"
 
+dotenv@^6.2.0:
+  version "6.2.0"
+  resolved "https://registry.yarnpkg.com/dotenv/-/dotenv-6.2.0.tgz#941c0410535d942c8becf28d3f357dbd9d476064"
+  integrity sha512-HygQCKUBSFl8wKQZBSemMywRWcEDNidvNbjGVyZu3nbZ8qq9ubiPoGLMdRDpfSrpkkm9BXYFkpKxxFX38o/76w==
+
 download-git-repo@^1.0.1, download-git-repo@^1.0.2:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/download-git-repo/-/download-git-repo-1.1.0.tgz#7dc88a82ced064b1372a0002f8a3aebf10eb1d3c"