fix(rsc): pass root importer explicitly instead of undefined for this.resolve in rsc:virtual-client-package

[nihgwu]

Description

@vitejs/plugin-rsc 0.5.28 added a project-root resolution check for client packages in #1277. In Rolldown builds, passing an undefined importer does not reliably represent the project root and can send importer-sensitive resolvers through a framework-owned dependency graph instead. In our case this caused runaway resolution and module-graph growth, ending in an OOM during the first RSC transform.

Resolve the package from the conventional /index.html importer explicitly. This preserves the #1277 behaviour: packages unavailable at the application root, or resolving to a different copy there, still fall back to the fully resolved module id.

Add a regression guard to the existing transitive client package fixture so build coverage fails if the root probe reaches another resolver without a concrete importer.

Reproduced with identical documentation content:

• @vitejs/plugin-rsc 0.5.27: build succeeds
• 0.5.28: build OOMs
• patched 0.5.28: build succeeds

Related to #1247 and #1277.

[nihgwu]

@hi-ogawa can you have a look, latest version blocks our builds 🙏

[hi-ogawa]

Doing this explicitly does make sense (I remember just seeing this on Vitest https://github.com/vitest-dev/vitest/blob/86c700ed8b77b7afb0ee9ec677ef8379f34a4bed/packages/vitest/src/node/plugins/vitestResolver.ts#L55) and fine to land nonetheless, but I'd appreciate more content on your setup.

Vite’s built-in resolver already resolves bare packages from the project root when the importer is undefined, so undefined and <root>/index.html should behave the same there. The reported difference therefore seems to come from another plugin handling this.resolve() first. Could you provide the full Vite config and plugin list from the failing setup so we can understand that interaction?

[hi-ogawa]

for above