vercel/ncc

github/core package fails build because of exports map

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#1311 opened on Mar 15, 2026

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bughelp wanted

Description

The @github/core package has the following exports:

  "exports": {
    ".": {
      "types": "./lib/core.d.ts",
      "import": "./lib/core.js"
    }
  }

In a project which has type: "module", and simply import * as core from '@github/core', we get the following error:

ncc: Version 0.38.4 ncc: Compiling file index.js into ESM ncc: Using typescript@5.9.3 (local user-provided) Error: Module not found: Error: Package path . is not exported from package /code/node_modules/@actions/core (see exports field in /code/node_modules/@actions/core/package.json) Did you mean './@actions/core'?

im guessing this is because whatever throws this error is looking for a default export rather than import. or it is mistakenly looking up the non-existent CJS entrypoint.

im not sure what dependency of ncc throws this error so i haven't managed to debug it myself.

Contributor guide

Tech stack
javascripttypescriptnodejs
Domain
build systemtooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
Understanding of Node.js module resolutionFamiliarity with package.json exports fieldKnowledge of ncc internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
The issue is that ncc fails to resolve a package with a conditional exports map that only provides an 'import' condition. The error suggests ncc is looking for a default or CJS entrypoint. Investigate how ncc resolves module paths, specifically in src/index.js or lib/ directory. Check how ncc handles the 'exports' field and 'type: module' in package.json. Look for any existing tests related to ESM bundling. Also examine the upstream dependency that throws the 'Module not found' error chain.