Xcode 11 Beta 3, build error "Unknown attribute 'State'", "Use of undeclared type 'View'" etc

This is from the Xcode 11 Beta 3 Release Notes.

Known Issues

• Xcode 11 doesn’t support working with SwiftUI in an iPad app brought to macOS. (41416222, 51201699)

I downloaded the Xcode 11 Beta 3 myself just to confirm the errors you mentioned, and I had the same issues when trying to build a SwiftUI project for Mac.

I would suggest going back to using Xcode Beta 2 if possible. Unfortunately, Apple doesn't provide download links to previous betas, so hopefully you have a Time Machine backup or Beta 2 still installed on your computer. Otherwise, you might be out of luck until the next beta is released.

Got same issue on Xcode 11.2. Found out that the reason was that somewhere in same module I declared protocol State {}. This breaks compiler without any reasonable errors.

I was getting the same "Unknown attribute 'State'" issue in Beta 5. But I was doing "@state" and not "@State". Case matters. It's hard to notice because both ways are shown as purple.