Polyfills not included when not using a full path as webpack entrypoint

[jimvandervoort]

Version

3.9.2

Reproduction link

https://github.com/jimvandervoort/vue-cli-entrypoint-reproduction

Environment info

Environment Info:

  System:
    OS: macOS 10.14.5
    CPU: (8) x64 Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
  Binaries:
    Node: 11.15.0 - /usr/local/bin/node
    Yarn: 1.17.0 - /usr/local/bin/yarn
    npm: 6.7.0 - /usr/local/bin/npm
  Browsers:
    Chrome: 75.0.3770.100
    Firefox: 67.0.4
    Safari: 12.1.1
  npmPackages:
    @vue/babel-helper-vue-jsx-merge-props:  1.0.0
    @vue/babel-plugin-transform-vue-jsx:  1.0.0
    @vue/babel-preset-app:  3.9.2
    @vue/babel-preset-jsx:  1.0.0
    @vue/babel-sugar-functional-vue:  1.0.0
    @vue/babel-sugar-inject-h:  1.0.0
    @vue/babel-sugar-v-model:  1.0.0
    @vue/babel-sugar-v-on:  1.0.0
    @vue/cli-overlay:  3.9.0
    @vue/cli-plugin-babel: ^3.9.0 => 3.9.2
    @vue/cli-plugin-eslint: ^3.9.0 => 3.9.2
    @vue/cli-service: ^3.9.0 => 3.9.2
    @vue/cli-shared-utils:  3.9.0
    @vue/component-compiler-utils:  2.6.0
    @vue/preload-webpack-plugin:  1.1.0
    @vue/web-component-wrapper:  1.2.0
    eslint-plugin-vue: ^5.0.0 => 5.2.3 (4.7.1)
    vue: ^2.6.10 => 2.6.10
    vue-eslint-parser:  5.0.0 (2.0.3)
    vue-hot-reload-api:  2.3.3
    vue-loader:  15.7.0
    vue-style-loader:  4.1.2
    vue-template-compiler: ^2.6.10 => 2.6.10
    vue-template-es2015-compiler:  1.9.1
  npmGlobalPackages:
    @vue/cli: Not Found

Steps to reproduce

Run yarn build.

Serve the dist directory and open in IE11.

What is expected?

console message 'hello' logged.

What is actually happening?

Error: Promise is undefined.

---

The issue can be fixed by changing the entrypoint from src/main to src/main.js. This bug happened after upgrading Vue CLI, we use multiple entrypoints in our project so we have a custom entry config in configureWebpack.

Quickly looking through the source I suspect it might have something to do with #3565, but I'm not sure.