Source maps broken for .esm.js file, work fine for non esm js files

Do you want to request a feature or report a bug? bug

What is the current behaviour? After updating from rc.4 to rc.10 source maps broken for all .esm.js files but work fine for non esm files eg. of a source map for file bundle.43470.esm.js - {"version":3,"sources":[],"names":[],"mappings":"","file":"bundle.43470.esm.js","sourceRoot":""}

If the current behaviour is a bug, please provide the steps to reproduce. run preact build with esm flag

What is the expected behaviour? source map generated should be correct

If this is a feature request, what is motivation or use case for changing the behaviour?

Please mention other relevant information.

Please paste the results of preact info here. Environment Info: System: OS: macOS Mojave 10.14.6 CPU: (8) x64 Intel® Core™ i7-4870HQ CPU @ 2.50GHz Binaries: Node: 10.16.3 - /usr/local/bin/node npm: 6.14.5 - /usr/local/bin/npm Browsers: Chrome: 83.0.4103.61 Firefox: 76.0.1 Safari: 13.1.1 npmPackages: preact: ^10.2.1 => 10.2.1 preact-cli: 3.0.0-rc.10 => 3.0.0-rc.10 preact-render-to-string: ^5.1.3 => 5.1.3 preact-router: ^3.1.0 => 3.1.0

[prateekbh]

this is the root cause of this: https://github.com/prateekbh/babel-esm-plugin/issues/46

[prateekbh]

we’re working on a final RC for this month