[vite 2.5 beta] change in addWatchFile breaks css dependency handling in vite-plugin-svelte

[dominikg]

Describe the bug

In this commit files added by addWatchFile are automatically appended to the importers dependencies in vite as a fix for vitejs/vite#3216

this breaks our current virtual handling via addditional file change events mentioned here vitejs/vite#3216 (comment)

Reproduction

• check out https://github.com/sveltejs/vite-plugin-svelte/tree/ci/vite-beta

pnpm i
pnpm test:ci:serve
# watch fails for svelte-preprocess

# manually running the test project works too, just revert before starting ci again
cd packages/e2e-tests/svelte-preprocess
pnpm dev
# start editing files in src/lib/multifile , add a new scss import like _foo.scss
# change stuff
# observe multiple events including js updates for the svelte component where only updates for the virtual css module should happen

Logs

https://github.com/sveltejs/vite-plugin-svelte/runs/3251554452?check_suite_focus=true#step:10:52

System Info

vite@2.5.0-beta.1

Severity

blocking an upgrade

[dominikg]

Possible solution: keep our own logic, but instead of addWatchFile, use server.watcher directly

[dominikg]

Another solution could be to try and split the dependencies returned by preprocess into ones that affect js output and ones that dont. unfortunately we don't know which were added by a style preprocessor, and even those could result in js updates if the resulting css affects js output.