Parcel: 🐛 amazon-cognito-identity-js dependency unresolved

[dfrkp]

🐛 BUG
When using parcel in a react project that also uses aws-amplify, parcel fails to resolve the dependency for amazon-cognito-identity-js even though it is correctly placed in node_modules/ by yarn.

Here is a repository with a minimal setup to reproduce the problem: https://github.com/dfrkp/parcel-test

🤔 Expected Behavior

A bundle is created even if aws-amplify is used.

😯 Current Behavior

$ yarn start                                                                                                                                                                                                                                                       [13:38:01]
  yarn run v1.5.1
  $ parcel index.html
  Server running at http://localhost:1234
🚨  /Users/user/Development/parcel-test/node_modules/aws-amplify/lib/Common/Facet.js:20:22: Cannot resolve dependency 'amazon-cognito-identity-js'
  18 | var AWS = require("aws-sdk/global");
  19 | exports.AWS = AWS;
> 20 | var Cognito = require("amazon-cognito-identity-js");
     |                       ^
  21 | exports.Cognito = Cognito;
  22 | var Pinpoint = require("aws-sdk/clients/pinpoint");
  23 | exports.Pinpoint = Pinpoint;

🌍 Environment

| Software | Version(s) |
| ---------------- | ---------- |
| Parcel | 1.6.2 |
| Node | 9.9 |
| Yarn | 1.5.1
| Operating System | macOS |

[gnijuohz]

This happens because parcel tries to load the module from es/index.js instead of lib/index.js, see https://github.com/parcel-bundler/parcel/blob/fc041d03c36bf41ea73c398e8d177de1a456e796/src/Resolver.js#L220-L224

However, the es folder doesn't exist.

IMO this is a bug from amazon-cognito-identity-js since that folder should be there. There is an issue reported there about this: https://github.com/aws/aws-amplify/issues/517

Parcel could try to see if the entry specified by "module" or "jsnext:main" exists or not first but I feel like that's not necessary.

[simonbuchan]

If you're going the extra mile, reporting the actual missing file (and why it was used) would be better than falling back to the first existing file, if that's what you meant.
A stronger motivation for fixing this would be monorepos - where it would make it clear you just haven't built yet, rather than that resolution is broken.