Unable to infer complex closure return type with SwiftUI

The issue is not with the closure, but with the isFavorite property on landmark.

It is not declared on the Landmark type, and the compiler instead of showing the undeclared property error, unable to resolve the stacks build closure return type, so it shows and error there.

Great job Apple tutorial writers and even better one Xcode11 compiler.

To fix:

1. Declare isFavorite variable on the Landmark type.
2. Make sure you update the landmarkData.json for every landmark record with the isFavorite = false entry, otherwise the app will crash at runtime.

For people getting this error on SwiftUI and looking for a way to debug their view stack

This error happens mainly when there is a compilation issue on one child View.

1 - Make sure your parent view can support multiple subviews (VStack, ZStack) and you have less than 10 subviews. Sometime you may want to add a Group wrapper.

2 - If this is not the problem, there is probably an issue with one subview. Try to isolate the one you suspect to have the issue. Usually I copy the subview into a property and a different error appears

var debug: some View {
        MyViewWithError(property: self.property)
}

Most of the time you'll encounter this because you pass the property (self.property) instead of a binding (self.$property)

Hope this can help some people

Some background to this problem

Like @dirtydanee already answered there is a difference between those two tutorials. But the problem behind the problem is that while it looks like you're doing a configuration it's actually just functions nested in functions using generics and protocols to "magically" parse everything into a compiling function.

However conformance to these generics and protocols need to be pretty precise because if not the whole tree of functions cannot compile anymore. But it's hard to determine for the compiler what conformance actually failed. This is why you see an error at the top rather than at the point where it actually happens.

It's strongly advised to make sure your views are decomposed into natural and simple blocks so you're not pouring over hundreds of lines of View code to find that one bug.

Dave DeLong had a really great talk about how to compose Views from ViewControllers that still holds true until today: basically you never use View as a subview inside another View but you need to decompose your View of many, simple Views. Otherwise these errors'll drive you nuts.