Describe the bug

Vite Config:

{
  "root": "web"
}

Project Structure:

web
├── index.html
├── main.ts
└── route.ts

A request to /route will unexpectedly serve /route.ts.

Since the file extension is omitted, I would expect for the traditional connect-history-api-fallback logic to apply and for /index.html to be served. If wanted to load the source file I would expect to have to make an explicit request for /route.ts. It doesn't seem right for the file extension to be inferred.

This is likely more of an issue for people like me who've configured root since that may mean source files sit at the top-level of root instead of nested inside of a src directory. Still, for cases such as this, this issue becomes more problematic as more source files and routes are created, since there's more opportunity for an inadvertent conflict.

Important: On the first load, you will actually see the correct fallback logic. It's only once vite has processed route.ts that the fallback behavior changes, and you'll start seeing a JavaScript file served instead of index.html.

Thanks for your help!

Reproduction

https://github.com/davezuko/reproductions/tree/master/vite-3502

Steps to reproduce:

1. Run yarn dev
2. Open http://localhost:3000, the app loads correctly
3. Open http://localhost:3000/test, the app loads correctly (renders "/test")
4. Open http://localhost:3000/route, the app serves /route.ts
5. Open http://localhost:3000/main, the app serves /main.ts

Alternate reproduction:

1. Run yarn dev
2. Open http://localhost:3000/route, the app loads correctly
3. Reload http://localhost:3000/route, the app now serves /route.ts

System Info

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

  System:
    OS: macOS 11.2.3
    CPU: (16) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 324.33 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 12.16.1 - ~/.n/bin/node
    Yarn: 1.22.4 - ~/.yarn/bin/yarn
    npm: 6.13.4 - ~/.n/bin/npm
  Browsers:
    Chrome: 90.0.4430.212
    Edge: 90.0.818.39
    Firefox Developer Edition: 78.0
    Safari: 14.0.3
  npmPackages:
    vite: ^2.3.3 => 2.3.3

Used package manager: yarn

Logs

  #####################
  Note this line, too
  #####################
  vite:resolve 1ms   /route -> /Users/zuko/projects/davezuko/reproductions/vite-xxxx/web/route.ts +0ms
  vite:spa-fallback Rewriting GET /route to /index.html +0ms
  vite:time 21ms  /index.html +0ms
  vite:resolve 1ms   /Users/zuko/projects/davezuko/reproductions/vite-xxxx/node_modules/vite/dist/client/client -> /Users/zuko/projects/davezuko/reproductions/vite-xxxx/node_modules/vite/dist/client/client.js +92ms
  vite:resolve 1ms   /@vite/client -> /Users/zuko/projects/davezuko/reproductions/vite-xxxx/node_modules/vite/dist/client/client.js +0ms
  vite:load 2ms   [fs] /@vite/client +0ms
  vite:resolve 0ms   ./env -> /Users/zuko/projects/davezuko/reproductions/vite-xxxx/node_modules/vite/dist/client/env.js +9ms
  vite:transform 9ms   /@vite/client +0ms
  vite:time 14ms  /@vite/client +88ms
  vite:resolve 1ms   /main.ts -> /Users/zuko/projects/davezuko/reproductions/vite-xxxx/web/main.ts +6ms
  vite:load 1ms   [fs] /main.ts +14ms

  #####################
  Here's where the file extension gets inferred
  vite:resolve 0ms   ./route -> /Users/zuko/projects/davezuko/reproductions/vite-xxxx/web/route.ts +21ms
  #####################

  vite:resolve 0ms   /route.ts -> /Users/zuko/projects/davezuko/reproductions/vite-xxxx/web/route.ts +1ms
  vite:transform 21ms  /main.ts +24ms
  vite:time 23ms  /main.ts +24ms
  vite:load 1ms   [fs] npm: vite +29ms
  vite:rewrite 0ms   [no imports] /Users/zuko/projects/davezuko/reproductions/vite-xxxx/node_modules/vite/dist/client/env.js +0ms
  vite:transform 0ms   npm: vite +9ms
  vite:time 2ms   npm: vite +9ms
  vite:load 2ms   [fs] /route.ts +2ms
  vite:rewrite 0ms   [no imports] route.ts +2ms
  vite:transform 2ms   /route.ts +3ms
  vite:time 4ms   /route.ts +3ms
  vite:spa-fallback Not rewriting GET /favicon.ico because the path includes a dot (.) character. +180ms
  vite:time 1ms   /favicon.ico +42ms

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