lazy() moduleUrl with a leading slash never resolves: dev emits //src/…, the build manifest lookup misses #390

Summary

A lazy() call whose hand-written moduleUrl has a leading slash ("/src/Page.tsx") never resolves. The plugin's key format is project-relative (src/Page.tsx), and nothing normalizes the slash:

• Dev: the generated URL becomes protocol-relative (//src/Page.tsx). The preload fetches http://src/Page.tsx and fails, and hydrate() falls back to a client render.
• Build: the client manifest has no /src/Page.tsx key. The server logs Asset manifest returned no client assets for module "/src/Page.tsx" and ships no root module map. On the client, hydration throws lazy() module "/src/Page.tsx" … was not preloaded before hydration, and reactivity halts.

This was split out of solidjs/solid#3338, where it reproduced the reporter's "page looks hydrated but every signal is dead" symptom.

Reproduction

From the reproduction on solidjs/solid#3338: the solid-v2/fullstack template (solid-js / @solidjs/web 2.0.0-rc.6, @solidjs/router 2.0.0-next.21, @solidjs/vite-plugin 3.0.0-next.39), with the <Loading> removed and a route component declared as:

const Page = lazy(() => import("./Page"), undefined, "/src/Page.tsx");

• Production build: the server logs Asset manifest returned no client assets for module "/src/Page.tsx". The client throws lazy() module "/src/Page.tsx" (hydration id "…") was not preloaded before hydration from the router outlet. Reactivity halts (REACTIVITY_HALTED).
• Dev: the root module map is serialized as //src/Page.tsx. The preload requests http://src/Page.tsx, fails, and the fallback client render dies with an unhandled Hydration Mismatch … key: undefined.

The same key without the slash ("src/Page.tsx") hydrates and stays reactive in both modes. See also the first diagnosis comment.

Expected behavior

A leading / on a moduleUrl key names the same module as the project-relative key. Either:

• it's normalized (/src/Page.tsx → src/Page.tsx) before the dev URL is built and before the build-manifest lookup, so both modes resolve the module; or
• if a leading slash is meant to be invalid, it's rejected with a clear error naming the expected project-relative format, not a silent miss.

Where it likely lives

A hand-written third argument bypasses the compiler's lazy() pass (transformLazy only rewrites one- and two-argument calls). So the user's string reaches the resolvers as-is.

• Dev: devModuleUrl in src/dev-manifest.ts and its mirror moduleUrl() in the generated devManifestCode in src/index.ts. Both build base + "/" + key, which gives //src/Page.tsx for a slash-prefixed key. The comment on devManifestCode says to keep the two in sync.
• Build: the virtual:solid-manifest load hook in src/index.ts exports the raw Vite manifest (via stampClientEntry). The key lookup itself is manifest[moduleUrl] in @solidjs/web's resolveAssets (packages/web/src/server.ts in solidjs/solid). The production half could be fixed on either side: the plugin normalizing keys in what it exports, or the runtime normalizing before lookup. That's worth deciding before a fix, so dev and build agree.

Related but distinct: #263 (Windows separators in generated keys), #298 (dev base and root-external keys), and #299 (query strings). None of them cover a leading slash on a hand-written key.

Filed on behalf of @ryansolid. — Claude via Cursor