Fix: Handle package.json exports field for sub-path imports (#47)

[konard]

Summary

This PR fixes issue #47 where use-m fails to resolve sub-path imports like yargs/helpers when they are defined in the package.json exports field.

Problem

When trying to import a package sub-path like yargs/helpers, use-m was failing with:

Error: Failed to resolve the path to 'yargs/helpers' from '/path/node_modules/yargs-v-latest/helpers'.

Root Cause

The issue had two parts:

1. Wrong package.json location: Reading package.json from the sub-path directory instead of the package root
2. Missing sub-path exports handling: Only checking for the root "." export, not sub-path exports like "./helpers"

Solution

Updated both npm and bun resolvers in use.mjs, use.js, and use.cjs to:

1. Added resolveExportsTarget helper - Handles both string exports and conditional export objects (import, default, require, etc.)

2. Updated tryResolveModule function signature - Now accepts:

   • modulePath: The full path to resolve
   • packageRootPath: The package root for reading package.json
   • subPath: The sub-path portion (e.g., "/helpers") for exports field lookup

3. Enhanced exports field resolution:

   • Reads package.json from the package root (not sub-path directory)
   • Checks for sub-path exports first (e.g., "./helpers": "./helpers/helpers.mjs")
   • Falls back to root "." export if no sub-path match
   • Properly resolves mapped file paths relative to package root

Testing

Reproduction Test

Created experiments/test-yargs-helpers.mjs that successfully imports both:

• yargs (main package)
• yargs/helpers (sub-path export)

Comprehensive Test Suite

Added tests/exports-field.test.mjs with tests for:

• yargs/helpers import with exports field
• Multiple versions ([email protected]/helpers, [email protected]/helpers)
• Actual functionality testing (hideBin function)
• @octokit/core as additional validation

Results

// ✅ Now works correctly:
const { hideBin } = await use('yargs/helpers');
const yargs17 = await use('[email protected]/helpers');
const yargs18 = await use('[email protected]/helpers');

Files Changed

• use.mjs - ES module version with fix
• use.js - Browser/universal version with fix
• use.cjs - CommonJS version with fix
• tests/exports-field.test.mjs - New comprehensive test suite
• experiments/ - Debug and reproduction scripts

Fixes

Closes #47

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]

[konard]

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[konard]

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