Describe the bug

If a specific file suffix is added as the resolve.extension field, vite allows its users to ignore the file suffix. However, when the user ignores the file suffix and uses the alias (@) to refer to a file in the project, an internal server error will occur. This error indicates that the file whose suffix is omitted does not exist. For example, if you add the .vue field in resolve.extension, you can omit the.vue suffix when referencing a vue file. However, in the case where we use @/path to refer to a file in the project, the project does not work properly. I will submit a PR to fix this problem!

Reproduction

https://github.com/ygj6/vite-issue-investigative/tree/alias_bug

In the main.js file, if user uses import App from '@/App' to refer to the App.vue. An error appears which indicates No loader is configured for ".vue" files: src/App.vue. However, there are two cases which can work as normal. For example, import App from './App or import App from '@/App.vue.

System Info

Output of npx envinfo --system --npmPackages vite,@vitejs/plugin-vue --binaries --browsers:

  System:
    OS: Windows 10 10.0.19041
    CPU: (8) x64 Intel(R) Core(TM) i5-10210U CPU @ 1.60GHz
    Memory: 15.51 GB / 23.74 GB
  Binaries:
    Node: 12.16.3 - D:\Program Files\nodejs\node.EXE
    Yarn: 1.22.4 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 6.14.4 - D:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: 90.0.4430.212
    Edge: Spartan (44.19041.964.0), Chromium (90.0.818.66)
    Internet Explorer: 11.0.19041.1

Used package manager:

Logs

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