Vite dev doesn't serve index.html from subdirectories of publicDir

[dhdaines]

Describe the bug

Vite's dev server behaviour for directories is subtly and maddeningly different for directories in root versus directories in publicDir. As described in great detail in the migration guide the behaviour is now consistent between dev and preview for root and depends on the presence of a trailing slash: /dir/ will route to /dir/index.html while /dir will route to /index.html.

For publicDir something else happens, namely that anything that isn't a specifically existing file seems to get routed to /index.html (like a SPA).

This behaviour doesn't seem to be documented anywhere, is inconsistent and not what I, a user, expect :-)

Reproduction

https://github.com/dhdaines/vitebug

Steps to reproduce

• Run npm install followed by npm run dev
• Navigate to http:https://localhost:5173/foo/ (should show "FOO", but instead shows the default front page)
• Navigate to http:https://localhost:5173/bar/ (shows "BAR")

System Info

System:
    OS: Linux 6.1 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
    CPU: (4) x64 Intel(R) Core(TM) i5-5300U CPU @ 2.30GHz
    Memory: 2.62 GB / 7.46 GB
    Container: Yes
    Shell: 5.2.15 - /bin/bash
  Binaries:
    Node: 20.14.0 - ~/.nvm/versions/node/v20.14.0/bin/node
    npm: 10.7.0 - ~/.nvm/versions/node/v20.14.0/bin/npm
  Browsers:
    Chrome: 126.0.6478.61
  npmPackages:
    vite: ^5.2.0 => 5.3.1

Used Package Manager

npm

Logs

Log for /foo/

  vite:html-fallback Rewriting GET /foo/ to /index.html +0ms
  vite:time 41.09ms /index.html +51ms                                      

Log for /bar/

  vite:html-fallback Rewriting GET /bar/ to /bar/index.html +1m
  vite:time 7.54ms /bar/index.html +1m

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[bluwy]

Duplicate of #6714