uni-app tree-shaking无效，请问怎么解决

[zvenshy]

问题描述
使用uni-app初始化的项目，发现无法tree shaking

复现步骤
项目初始化流程

vue create -p dcloudio/uni-preset-vue my-project
// 之后选择默认模板(typescript)

demo:

// src/src.ts
export const a = "12345";
export const b = "b12345";
export const c = 3;

// src/src1.ts
export const aa = "a111111";
export const bb = 22222;
export const cc = 333333;

// src/demo.ts
import { a, b, c } from "@/src";
import { aa, bb, cc } from "@/src1";

export { a, b, c, aa, bb, cc };

// src/App.vue
    import { a } from "./demo";

    console.log("TCL: a", a);

期望的结果是 shake 掉 src/src1.ts 的代码,因为我并没有用到其中的代码。但不行。结果如下：

// 运行命令：yarn build:mp-weixin
// dist/build/mp-weixin/common/vendor.js
var r="a111111";e.aa=r;var o=22222;e.bb=o;var i=333333;e.cc=i

定位了一下发现修改 babel.config presets 即可

//babel.config.js
module.exports = {
  presets: [
    [
      "@vue/app",  // "@vue/cli-plugin-babel/preset"也行的
      {
        modules: false, // modules: 'commonjs' => false
        useBuiltIns: process.env.UNI_PLATFORM === "h5" ? "usage" : "entry"
      }
    ]
  ],
  plugins
};

本以为问题解决，结果乐极生悲。当依赖 components 时编译又有问题。代码如下

// src/compDemo.vue
<template>
    <div class="hello">
        <h1>{{ msg }}</h1>
        <p>
            For a guide and recipes on how to configure / customize this project,
            <br>check out the
            <a href="https://cli.vuejs.org" target="_blank" rel="noopener">vue-cli documentation</a>.
        </p>
    </div>
</template>

<script>
    export default {
        name: "HelloWorld",
        props: {
            msg: String
        }
    };
</script>


// src/page/index/index.vue
<template>
	<view class="content">
        <image class="logo" src="../../static/logo.png"></image>
		<view>
            <text class="title">{{title}}</text>
        </view>
		<comp-demo></comp-demo>
	</view>
</template>

<script lang="ts">
	import Vue from 'vue';
	import compDemo from "../../compDemo.vue";
	export default Vue.extend({
		components: {
            compDemo
        },
		data() {
			return {
				title: 'Hello'
			}
		},
		onLoad() {

		},
		methods: {

		}
	});
</script>

报错信息如下：

TypeError: Cannot read property 'id' of undefined
    at Object.keys.forEach.name (/Users/xxxx/my-project/node_modules/@dcloudio/webpack-uni-mp-loader/lib/plugin/generate-component.js:57:15)
    at Array.forEach (<anonymous>)
    at generateComponent (/Users/xxxx/my-project/node_modules/@dcloudio/webpack-uni-mp-loader/lib/plugin/generate-component.js:24:25)
    at Promise (/Users/xxxx/my-project/node_modules/@dcloudio/webpack-uni-mp-loader/lib/plugin/index-new.js:84:11)
    at new Promise (<anonymous>)
    at compiler.hooks.emit.tapPromise.compilation (/Users/xxxx/my-project/node_modules/@dcloudio/webpack-uni-mp-loader/lib/plugin/index-new.js:72:16)
    at _next2 (eval at create (/Users/xxxx/my-project/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:9:17)
    at _err2 (eval at create (/Users/xxxx/my-project/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:26:1)
    at callback (/Users/xxxx/my-project/node_modules/copy-webpack-plugin/dist/index.js:77:17)
    at /Users/xxxx/my-project/node_modules/copy-webpack-plugin/dist/index.js:118:24
error Command failed with exit code 1.

可以看出修改 presets 后，webpck-uni-mp-loader 在执行时会出错

请问该如何实现 tree shaking 呢？

[或者可以直接贴源代码]

预期结果
能够shake掉无用代码

系统信息:

• 发行平台:微信小程序

uni-app v2.3.7
uni-app cli v2.0.0-23720191024001

Environment Info:

System:
OS: macOS 10.14.6
CPU: (8) x64 Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz
Binaries:
Node: 10.15.0 - ~/.nvm/versions/node/v10.15.0/bin/node
Yarn: 1.17.3 - /usr/local/bin/yarn
npm: 6.4.1 - ~/.nvm/versions/node/v10.15.0/bin/npm
npmPackages:
@dcloudio/types: * => 0.4.1
@dcloudio/uni-app-plus: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-app-plus-nvue: 0.0.1
@dcloudio/uni-app-plus-nvue-v8: 0.0.1
@dcloudio/uni-cli-shared: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-h5: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-helper-json: * => 1.0.3
@dcloudio/uni-mp-alipay: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-mp-baidu: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-mp-qq: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-mp-toutiao: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-mp-weixin: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-stat: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/uni-template-compiler: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/vue-cli-plugin-hbuilderx: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/vue-cli-plugin-uni: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/vue-cli-plugin-uni-optimize: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/webpack-uni-mp-loader: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@dcloudio/webpack-uni-nvue-loader: 0.0.1
@dcloudio/webpack-uni-pages-loader: ^2.0.0-23720191024001 => 2.0.0-23720191024001
@vue/babel-helper-vue-jsx-merge-props: 1.0.0
@vue/babel-plugin-transform-vue-jsx: 1.0.0
@vue/babel-preset-app: 3.12.1
@vue/babel-preset-jsx: 1.1.1
@vue/babel-sugar-functional-vue: 1.0.0
@vue/babel-sugar-inject-h: 1.0.0
@vue/babel-sugar-v-model: 1.1.1
@vue/babel-sugar-v-on: 1.1.0
@vue/cli-overlay: 4.0.5
@vue/cli-plugin-babel: 3.5.1 => 3.5.1
@vue/cli-plugin-router: 4.0.5
@vue/cli-plugin-typescript: ^3.5.1 => 3.12.1
@vue/cli-plugin-vuex: 4.0.5
@vue/cli-service: ^4.0.0 => 4.0.5
@vue/cli-shared-utils: 3.12.1
@vue/component-compiler-utils: 3.0.0
@vue/preload-webpack-plugin: 1.1.1
@vue/web-component-wrapper: 1.2.0
mpvue-page-factory: 1.0.1
mpvue-template-compiler: 1.0.13
uni-h5-vue: 2.6.10
uni-mp-vue: 2.6.10
vue: ^2.6.10 => 2.6.10
vue-class-component: ^6.3.2 => 6.3.2 (7.1.0)
vue-hot-reload-api: 2.3.4
vue-loader: 15.7.1
vue-property-decorator: ^8.0.0 => 8.3.0
vue-router: 3.0.1
vue-style-loader: 4.1.2
vue-template-compiler: ^2.6.10 => 2.6.10
vue-template-es2015-compiler: 1.9.1
vuex: ^3.0.1 => 3.1.1
npmGlobalPackages:
@vue/cli: 3.9.3

补充信息
可以看出修改 presets 后，webpck-uni-mp-loader 在执行时会出错

[zvenshy]

补充：template 模板编译模式没有问题，是自定义组件编译模式会报错。应该是有坑。望修复

[zvenshy]

@zhetengbiji @fxy060608 @Wangyaqi 麻烦看下？

[zhangchenna]

我也是遇到了同样的问题 Cannot read property 'id' of undefined