fix(rsc): respect vite config root (fix #1126)

[vixalien]

Description

cc @hi-ogawa I couldn't figure out how to add a test for this

Fix #1126

[vixalien]

FYI, build still fails after this patch:

node ../runner/index.js
vite v7.1.6 building for production...
🧪 Using React Router's RSC Framework Mode (experimental)
✓ 47 modules transformed.
✗ Build failed in 1.33s
node:internal/modules/run_main:107
    triggerUncaughtException(
    ^

[rsc:virtual:vite-rsc/assets-manifest] Cannot convert undefined or null to object
    at Object.values (<anonymous>)
    at Object.generateBundle (file:///home/alien/sites/repro-react-router-rsc-runner/node_modules/.pnpm/@vitejs+plugin-rsc@0.5.21_react-dom@19.2.4_react@19.2.4__react@19.2.4_vite@7.1.6_@types_4b5722990c6258b73efc205a6ffdd2ee/node_modules/@vitejs/plugin-rsc/dist/plugin.js:558:36)
    at Object.handler (file:///home/alien/sites/repro-react-router-rsc-runner/node_modules/.pnpm/vite@7.1.6_@types+node@24.5.2_jiti@2.6.1_lightningcss@1.30.1/node_modules/vite/dist/node/chunks/dep-D5b0Zz6C.js:34064:13)
    at file:///home/alien/sites/repro-react-router-rsc-runner/node_modules/.pnpm/rollup@4.59.0/node_modules/rollup/dist/es/shared/node-entry.js:22571:40
    at processTicksAndRejections (node:internal/process/task_queues:104:5) {
  code: 'PLUGIN_ERROR',
  plugin: 'rsc:virtual:vite-rsc/assets-manifest',
  hook: 'generateBundle'
}

Node.js v25.7.0

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@vitejs/plugin-react@1133

npm i https://pkg.pr.new/@vitejs/plugin-react-oxc@1133

npm i https://pkg.pr.new/@vitejs/plugin-rsc@1133

npm i https://pkg.pr.new/@vitejs/plugin-react-swc@1133

commit: 32104dd

[hi-ogawa]

It looks like there are more moving parts related to root than I expected. We should aim for making examples/starter work by vite dev examples/starter from elsewhere probably.

[hi-ogawa]

It turned out we already have related test case.

vite-plugin-react/packages/plugin-rsc/e2e/root.test.ts

Lines 7 to 33 in 98387ae

	test.describe(() => {
	const root = 'examples/e2e/temp/root'
	test.beforeAll(async () => {
	await setupInlineFixture({
	src: 'examples/starter',
	dest: root,
	files: {
	'vite.config.base.ts': { cp: 'vite.config.ts' },
	'vite.config.ts': /* js */ `
	import baseConfig from './vite.config.base.ts'
	import path from "node:path";
	baseConfig.root = "./custom-root";
	for (const e of Object.values(baseConfig.environments)) {
	e.build.rollupOptions.input.index = path.resolve(
	'custom-root',
	e.build.rollupOptions.input.index,
	);
	}
	export default baseConfig;
	`,
	},
	})
	fs.mkdirSync(`${root}/custom-root`, { recursive: true })
	fs.renameSync(`${root}/src`, `${root}/custom-root/src`)
	fs.renameSync(`${root}/public`, `${root}/custom-root/public`)
	})

Switching from process.cwd() to config.root would technically break this use case where config file lives in process.cwd() and the only app code is under config.root. We probably need to crawl both.