Fast discovery misses TypeScript NodeNext `.js` specifiers → silent WorkflowNotRegisteredError

Open
#3,151 1 comment 0 reactions 1 assignee View on GitHub

@ijjk is already working on this.

Since Jul 28, 2026.

Assessment

This issue has not been assessed yet.

Description

Summary

A .ts file using TypeScript NodeNext-style specifiers — export * from './x.js' (what TS itself prescribes) — is invisible to workflow fast discovery. The build succeeds, the workflow/step never registers, and the first signal is a runtime WorkflowNotRegisteredError. esbuild resolves the same specifier fine during bundling, so only the discovery pass is affected.

Where

  • packages/builders/src/fast-discovery.ts:754-757 — .js is in FAST_DISCOVERY_SOURCE_EXTENSION_SET, so the resolver does a bare fileExists on x.js and returns null without ever reaching the candidate-extension loop below.
  • packages/builders/src/fast-discovery.ts:889-890 — relative specifiers go through that function only; there is no enhanced-resolve fallback for them.
  • packages/builders/src/fast-discovery.ts:24-30 — the enhanced-resolve instance used for bare specifiers is constructed without extensionAlias, so deep package imports have the same hole.
  • packages/builders/src/fast-discovery.ts:944-946 — unresolved edges are dropped with a bare return, no diagnostic, which is why the failure is silent.
  • packages/builders/src/fast-discovery.test.ts uses .js specifiers (151, 207, 269, 765) but always against real .js files on disk, so this case is untested.

Suggested fix

Contained: in resolvePathLikeSpecifier, on a .js/.jsx/.mjs/.cjs miss, retry the .ts/.tsx/.mts/.cts candidates before returning null (i.e. implement the extensionAlias semantics), and consider emitting a diagnostic when a directive-bearing edge fails to resolve instead of dropping it silently.

Impact

This hits any TypeScript library author following NodeNext module resolution — exactly the audience of the publishing-libraries cookbook. Found while building the Mastra integration (@mastra/workflow), where it cost a debugging cycle.

Dominant language
TypeScript
Stars
2.4k
Forks
365
Avg merge
2d 6h
Merged PRs (30d)
164

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from vercel/workflow

All issues in vercel/workflow

Similar issues

More TypeScript issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.