Interesting, the tests' type checker couldn't do that inference, I think due to handle(error:_).

Edit:
After a minimal playground test, seems like so. I see now that the interference was removed from the function return type, but strange that it works on my machine (cleaned and everything). However, the test below doesn't work on my machine. 🤷

Edit edit:
Seems like a Swift 5.6 issue.

let handleWarningAsError = false

func handle<T>(warning: String) -> T? {
    if handleWarningAsError {
        fatalError()
    } else {
        print(warning)
        return nil
    }
}

let keys = ["foo", "bar"]

struct Property {
    
    let name: String
    let uuid = UUID()
}

let properties = keys.compactMap { key in // Error: ambiguous, fix with [Property]
    
    if key == "foo" {
        return handle(warning: "You are foo, I don't like you")
    }
    
    return Property(name: key)
}

print(properties)

@liamnichols I apologize for the ping, could this and #177 receive a review as I would like to go ahead with some work that would use these features. Thank you!