refactor: consistent build target env variable

Author: yyx990803

packages/@vue/babel-preset-app/index.js

@@ -59,7 +59,7 @@ module.exports = (context, options = {}) => {
   // useBuiltIns: 'usage' we won't be running Babel on these deps, they need to
   // be force-included.
   let polyfills
-  const buildTarget = process.env.VUE_CLI_TARGET || 'app'
+  const buildTarget = process.env.VUE_CLI_BUILD_TARGET || 'app'
   if (
     buildTarget === 'app' &&
     useBuiltIns === 'usage' &&

packages/@vue/cli-service/lib/commands/build/index.js

@@ -43,6 +43,7 @@ module.exports = (api, options) => {
       args.entry = args.entry || 'src/App.vue'
     }
 
+    process.env.VUE_CLI_BUILD_TARGET = args.target
     if (args.modern && args.target === 'app') {
       process.env.VUE_CLI_MODERN_MODE = true
       delete process.env.VUE_CLI_MODERN_BUILD
@@ -59,8 +60,9 @@ module.exports = (api, options) => {
       delete process.env.VUE_CLI_MODERN_MODE
       delete process.env.VUE_CLI_MODERN_BUILD
     } else {
-      return build(args, api, options)
+      await build(args, api, options)
     }
+    delete process.env.VUE_CLI_BUILD_TARGET
   })
 }
 
@@ -100,7 +102,6 @@ async function build (args, api, options) {
   const isLegacyBuild = args.target === 'app' && args.modern && !args.modernBuild
 
   // resolve raw webpack config
-  process.env.VUE_CLI_BUILD_TARGET = args.target
   let webpackConfig
   if (args.target === 'lib') {
     webpackConfig = require('./resolveLibConfig')(api, args, options)

packages/@vue/cli-service/lib/commands/build/resolveLibConfig.js

@@ -2,8 +2,6 @@ const fs = require('fs')
 const path = require('path')
 
 module.exports = (api, { entry, name }, options) => {
-  // setting this disables app-only configs
-  process.env.VUE_CLI_TARGET = 'lib'
   // inline all static asset files since there is no publicPath handling
   process.env.VUE_CLI_INLINE_LIMIT = Infinity
 

packages/@vue/cli-service/lib/commands/build/resolveWcConfig.js

@@ -2,8 +2,6 @@ const path = require('path')
 const { resolveEntry, fileToComponentName } = require('./resolveWcEntry')
 
 module.exports = (api, { target, entry, name }) => {
-  // setting this disables app-only configs
-  process.env.VUE_CLI_TARGET = 'web-component'
   // Disable CSS extraction and turn on CSS shadow mode for vue-style-loader
   process.env.VUE_CLI_CSS_SHADOW_MODE = true
 

packages/@vue/cli-service/lib/config/app.js

@@ -5,7 +5,7 @@ const path = require('path')
 module.exports = (api, options) => {
   api.chainWebpack(webpackConfig => {
     // only apply when there's no alternative target
-    if (process.env.VUE_CLI_TARGET) {
+    if (process.env.VUE_CLI_BUILD_TARGET && process.env.VUE_CLI_BUILD_TARGET !== 'app') {
       return
     }