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After 2866d4f, we have opt-in for build plugins to be shared, matching the way things work during dev.
Individual plugins can set a sharedDuringBuild: true to opt-in, or all plugins can be forced to be shared using builder: { sharedPlugins: true } (this will probably break most plugins right now). There is also a builder: { sharedConfigBuild: true } to directly share the whole config. This will break even more plugins, even ours internally because right now we are all using config.build instead of environment.options.build.

We can deprecate config.build for ResolvedBuildOptions because these are the defaults and shouldn't be used. And later on directly remove config.build after resolving forcing everyone to use environment.options (this is the same we already were discussing to with config.resolve). I think this may be one of the trickiest parts in getting the ecosystem to move. We could always leave an opt-in into backward compatibility when we reach this point.

One interesting problem about shared plugins is that once they are used, the only command that makes sense is vite build --app. Building a single environment could fail because the author of the plugin has the expectation of the plugin processing both client and ssr code for example. This is equivalent to what happens now in SvelteKit and other frameworks where building only ssr doesn't work because you need to build the client first, get the SSR manifest and use it to build the ssr (and they do all this in a single vite build).
So maybe we should not have vite build --environment={name} at all, and have some config opt-in to vite build being vite build --app instead of a CLI option.
Does it ever makes sense to build only a part of an app with Vite? If it is about performance, I think that may need to be cached in a diff way.

/ecosystem-ci run

📝 Ran ecosystem CI on 0250864: Open

✅ analogjs, ladle, laravel, marko, nuxt, previewjs, quasar, qwik, rakkas, redwoodjs, storybook, unocss, vite-environment-examples, vite-plugin-pwa, vite-plugin-react, vite-plugin-react-swc, vite-plugin-svelte, vite-plugin-vue, vite-setup-catalogue, vitepress, vuepress

Current ecosystem CI state in the Environment API PR. We're all green in main, so we know that these are produced by the new changes:

• astro: A single CSS test is failing (@sapphi-red's explanation of the issue here
• remix, vike: expectation to HMR or reload the client when a SSR only module is changed. We consider that this is a bug fix and wasn't intended before. This should be handled on the framework side
• histoire, vitest: there are PR to fix these that haven't been merged yet

Note: SvelteKit was passing before, it is failing in main now too. It is unrelated to this PR.

We discussed in today's Vite team meeting that we should merge this PR so we move further work to main. The changes in this PR are now backward compatible (see ecosystem-ci comment above) and all new APIs are experimental. We can continue refining them during the Vite 6 beta period that we will start now (and even after the stable release, we'll have opportunities for changes if needed until these are stabilized in 6.x).
Thanks everyone for all the work to get this PR to this point 🎉

@Scutua please don't approve old PRs in the repo, or we'll need to ban you from the org for spamming.