Solid plugin config function causes issues with Vitest 3.0

[pedro00dk]

Hi!

I had an issue when trying to use solid-js with vitest and stumbled on an issue. Not to repeat myself, please check the vitest issue vitest-dev/vitest#7284 .

According to one of vitest authors, the tl;dr is:

Returning an object from a config hooks will merge that object with an existing config, this is how this hook works: https://vite.dev/guide/api-plugin.html#config
This is a bug in solidjs plugin, do not return already resolved object. Either modify the config or return a partial object that will be merged with an existing config.**

Related: #101
It seems there where attempts to fix a similar issue before.

[simonihmig]

I can confirm this issue, just ran ino it myself.

Seems the config hook is returning the full test object here that it received as input, causing the duplication in the browser.instances array after the deep merge.

[simonihmig]

I got around it for now by patching locally to not return the test object. Ok-ish as a temporary workaround, but I don't think this fix is PR-worthy, as the plugin should really decide how it wants to use the config hook: either mutate or return the config to be merged, but not both (as suggested on the vitest issue linked above).