Turbopack: trace externals imported only by server actions#95824
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mischnic
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Thankfully these annoying additional_entries will be removed soon anyway.
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#95815 refactored the NFT flow and ended up only tracing the RSC template and it's subgraph. Not the server actions loader module whose module graph is completely separate.
Clauded.
Attempts to fix #95130 (reply in thread).
Details
Summary
Fixes the NFT tracing regression behind #95815 and the deploy failures reported in #87737 (comment).
Since the 16.3 NFT rewrite (#94224 / #92901), a
serverExternalPackagesentry that is imported only from a'use server'action referenced by a client component ends up in the route's trace as the content-hashed alias symlink (.next/node_modules/<pkg>-<hash>) without the store files the symlink points to. Any output assembled from the traces (Vercel lambdas,output: 'standalone') then contains a dangling symlink, and invoking the action throwsFailed to load external module <pkg>-<hash>(HTTP 500). 16.2.9 traces both. Both CJS and ESM externals are affected, with any package manager — the ESM/bun/monorepo framing in the issue reports was a coincidence of which packages were only reachable through actions.The cause:
AppEndpoint::trace_resultstarted the trace DFS only fromrsc_entry, but the server actions loader is a separate module-graph entry (additional_entries). It is chunked into the endpoint output (which emits the alias symlink via the chunk's output assets), yet its subgraph — including the externals' traced target files — was never visited by the tracer.trace_endpointnow accepts multiple entry modules and the app endpoint passes the actions loader alongsidersc_entry.The test observes the user-visible failure: it builds with
output: 'standalone', deletes everything except the standalone output (so only traced files are available, like a deployed lambda), runsserver.js, and invokes the server action in a browser. Without the fix the action fails withFailed to load external module lodash-<hash>; on 16.2.9 the same fixture responds with the action result. Note the fixture must not import the externals from any other route: the standalone output is the union of all route traces, so a route that traces them correctly would mask the missing entries.Verification
pnpm test-start-turbo test/production/standalone-mode/server-action-externals/standalone-mode-server-action-externals.test.ts— fails without the fix (Failed to load external module lodash-fb78ad0536ffcdabfrom the standalone server), passes with it. The equivalent standalone flow onnext@16.2.9returns the action result with HTTP 200.pnpm test-start-turbo test/e2e/externals-transitive/externals-transitive.test.tspnpm test-start-turbo test/production/standalone-mode/server-actions/standalone-mode-server-actions.test.ts