What does the `duplicate content roots` warning me...

# intellij

[Brendan Weinstein]

What does the duplicate content roots warning message mean? I am seeing this in a multiplatform project that uses a plugin to generate code for commonMain sourceset and having trouble figuring out how to address. For a bit more detail see https://kotlinlang.slack.com/archives/C5HT9AL7Q/p1586533843040100