Demonstration how compiler cannot infer that typed errors are exhausted

1-works_fine.swift

enum MyError: Error {
    case failureA
    case failureB
}

func produceFailure() throws(MyError) -> Int {
    throw .failureB
}

do throws(MyError) {
    let result = try produceFailure()
    print("Result:", result)
} catch MyError.failureA {
    print("Failure A")
} catch MyError.failureB {
    print("Failure B")
}

2-compiler_error.swift

enum MyError: Error {
    case failureA
    case failureB
}

func produceFailure() throws(MyError) -> Int {
    throw .failureB
}

func anotherFunction() {
    do throws(MyError) {
        let result = try produceFailure()
        //           `- error: errors thrown from here are not handled because the enclosing catch is not exhaustive
        print("Result:", result)
    } catch MyError.failureA {
        print("Failure A")
    } catch MyError.failureB {
        print("Failure B")
    }
}

anotherFunction()

3-compiler_warning.swift

enum MyError: Error {
    case failureA
    case failureB
}

func produceFailure() throws(MyError) -> Int {
    throw .failureB
}

func anotherFunction() {
    do throws(MyError) {
        let result = try produceFailure()
        print("Result:", result)
    } catch MyError.failureA {
        print("Failure A")
    } catch MyError.failureB {
        print("Failure B")
    } catch {  
    // `- warning: case will never be executed 
        print("Failure:", error)
    }
}

anotherFunction()

NB: The code doesn't work in a Playground. At all.