Xcode 9 / Swift 4 migration error

Question

I'm receiving errors when trying to automatically migrate to swift 4.

I'm getting "unexpected duplicate task" when trying to migrate a workspace with multiple targets.

Answer 1

Reference From BEm answer

I had the same problem. In my app I have three target

• Dev
• Pre
• Prod

App was running in Dev but not in Pre & Prod.

When I open my under File > Workspace Settings, I had below (New Build System(Default))

I changed it to (Legacy Build System)

And it was a fix for me.

Answer 2

Had the same error when trying to migrate to swift 4. Check if you did enable the "New Build System (Preview)" under File > Workspace Settings. If you enabled it make sure to set it back to "Standard Build System". Did solve the problem for me.