• Version: v12.3.1
• Platform: Linux thinkpad-avaq 4.19.47 #1-NixOS SMP Fri May 31 13:46:35 UTC 2019 x86_64 GNU/Linux

Preparation

1. Go to a temporary directory: cd $(mktemp -d)
2. Install Fluture or any other module that has a "main" field without file extension, and contains a .js main file as well as a .mjs main file: npm install fluture@11.0.1

Reproducing

Run the following two shell scripts:

node --input-type=module \
     --experimental-modules \
     --eval 'import Future from "fluture"; console.log(Future)'

echo 'import Future from "fluture"; console.log(Future)' > index.mjs
node --experimental-modules index.mjs

Expected result

The output of both shell scripts is the same.

Actual result

The first script errors with Error: Cannot find package 'fluture' imported from, and the output from the second shows that the module resolver loaded the CommonJS version of the package into the module.

_{/cc @ljharb}