No error message when index.html file is missing

Describe the bug

If there is no index.html file present then running vite shows no errors and trying to access the page will give a 404 server error. Although having a missing index.html file is obviously wrong and unlikely to happen if using the cli, it’s easy to forget to add one if migrating an existing project from web pack to vite. I would expect vite to show some error message that no html file was found.

Reproduction

1. Use the cli to create a vite project.
2. Remove the index.html file.
3. Run ‘npm run dev’

There will be no error message. Trying to access the page will show a 404 error.

System Info

• vite version: 2.0.0-beta.30
• Operating System: MacOS 11.1
• Node version: 14.4.0
• Package manager (npm/yarn/pnpm) and version: npm 6.14.11

[yyx990803]

To serve custom virtual html you need to add a custom middleware using the configureServer plugin hook because HTML is not handled as part of the normal transforms during dev.

[yyx990803]

Closing since this is expected - open to a PR to provide more descriptive error message for this though.