Asset name conflicts are possible in manifest.json, causing unexpected / missing asset loading

[gryphonmyers]

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Describe the bug

It seems that if you have an entrypoint that shares a base name with one of your asset chunks, the manifest file that ultimately gets written will suffer from loss preventing you from doing a successful backend integration.

In my repro note the following:

• I have changed the entrypoint to src/main.js in the vite config
• main.vue is a dynamic import so will get its own css asset chunk
• Building the site, you will see it generates two css files with basename of main (one for the entrypoint, one for the dynamic chunk).
• Note that the manifest file only has a single "main.css" record. It is ambiguous which one it refers to, but from my experience it actually ends up referring to the dynamic chunk, meaning that a record of the entrypoint styles are lost.

Reproduction

https://github.com/gryphonmyers/vite-minimal-repro/tree/manifest-name-conflict

System Info

• vite version: 2.0.0-beta.35
• Operating System: macos 10.15.7
• Node version: 14.15.1
• Package manager (npm/yarn/pnpm) and version: npm 6.14.8

[yyx990803]

With cf81aa3 it now generates something like this:

{
  "main.js": {
    "isEntry": true,
    "isDynamicEntry": false,
    "file": "assets/main.a4557f7e.js",
    "imports": [],
    "dynamicImports": [
      "assets/main.333f1426.js"
    ],
    "facadeModuleId": "src/main.js"
  },
  "main-1.js": {
    "isEntry": false,
    "isDynamicEntry": true,
    "file": "assets/main.333f1426.js",
    "imports": [
      "assets/main.a4557f7e.js"
    ],
    "dynamicImports": [],
    "facadeModuleId": "src/components/main.vue"
  },
  "main.css": {
    "file": "assets/main.6f5e5b3c.css"
  },
  "main-1.css": {
    "file": "assets/main.2a664265.css"
  }
}

Not ideal but it preserves backwards compat. We may consider a better manifest format in the future but that might be a breaking change.