`build --watch` doesn't watch files in `public`

[Skn0tt]

Describe the bug

It appears that vite build --watch only copies over public once when initialised, instead of watching them. We expect them to be watched just like other source files.

We use Vite to build a website with a service worker into a static directory, so that our custom HTTP server can pick it up. The website has a service worker and it needs different build settings than the main site. We have a separate vite build --watch --outDir=public --config=vite.sw.config.ts process that does that. We expect the main vite build --watch process to watch file changes in public just like it watches file changes from outher sources, and we expect it to sync those changes into its out dir so our custom HTTP server can pick them up.

Reproduction

https://github.com/Skn0tt/vite-build-watch-public-repro

Steps to reproduce

1. npm ci
2. npx vite build --watch
3. edit contents of public/foo

expected: dist/foo contains updated content

actual: dist/foo contains content old content from when npx vite build --watch was started

System Info

System:
    OS: macOS 15.1
    CPU: (12) arm64 Apple M3 Pro
    Memory: 125.64 MB / 18.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.7.0 - ~/.nvm/versions/node/v22.7.0/bin/node
    Yarn: 1.22.22 - ~/.nvm/versions/node/v22.7.0/bin/yarn
    npm: 10.8.2 - ~/.nvm/versions/node/v22.7.0/bin/npm
    pnpm: 9.6.0 - ~/.nvm/versions/node/v22.7.0/bin/pnpm
  Browsers:
    Chrome: 131.0.6778.70
    Edge: 130.0.2849.80
    Safari: 18.1
  npmPackages:
    vite: ^5.4.11 => 5.4.11

Used Package Manager

npm

Logs

No response

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[nguyenbatranvan]

Do you already have a solution for this issue?

[Skn0tt]

This is our workaround: https://github.com/microsoft/playwright/blob/b83e0af11aefacaf220d3f60938aeb450dcb984f/utils/build/build.js#L308-L311

[ValentinYoushkevich]

Opened #23245 for this.

Turned out to be a small fix: the plugin that copies publicDir already re-copies it on every rebuild, so the only missing piece was that nothing ever put those files in the watch set — a change under public/ didn't trigger a rebuild at all. buildStart now registers them with addWatchFile().

One gap worth knowing about: creating a new file in public/ doesn't rebuild right away, since it didn't exist when the watch set was built. It gets picked up on the next rebuild. Editing and deleting work.