fix(externals)!: fall back to mlly resolver in more cases

[danielroe]

🔗 Linked issue

context: nuxt/nuxt#14629

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

In the linked issue above, the presence of a directory express was skipping the mlly resolution process as the path existed. I've added a couple of additional conditions here:

1. resolve with mlly if id is not absolute (express.js) won't map to ~/express.js in node terms
2. resolve with mlly if id is a directory - as directory imports won't work in esm and we need to resolve /index.js
3. only call normalizeid on absolute paths as otherwise (if mlly absolutely can't resolve it) we can end up with something like file://express

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #431 (ed112e5) into main (d0029c0) will decrease coverage by 0.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##             main     nuxt/nuxt.js#11753      +/-   ##
==========================================
- Coverage   53.54%   53.53%   -0.02%     
==========================================
  Files          54       54              
  Lines        3565     3566       +1     
  Branches      377      378       +1     
==========================================
  Hits         1909     1909              
  Misses       1293     1293              
- Partials      363      364       +1     

Impacted Files	Coverage Δ
src/rollup/plugins/externals.ts	63.82% <33.33%> (-0.27%)	⬇️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[pi0]

Would you please provide a (nitro) reproduction? 🙏🏼

[danielroe]

I believe the fix makes sense on its own for the reasons mentioned in the description.

But here you go: https://stackblitz.com/edit/nuxt-starter-qlsvtz.

[pi0]

LGTM to include in next semver-major since this change is risky somehow.

For next PRs, please use a minimal nitro reproduction to help me review faster 🙏🏼