Comment by xedin

This is the diagnostic produced for similar example using new diagnostic architecture:

error: binary operator '+' cannot be applied to operands of type 'String' and 'Int'

_ = "a" + 1

   ~~~ ^ ~

note: overloads for '+' exist with these partially matching parameter lists: (Int, Int), (String, String)

_ = "a" + 1

       ^

note: candidate expects value of type 'String' for parameter #2

    @inlinable public static func + (lhs: String, rhs: String) -> String
                                  ^

note: candidate expects value of type 'Int' for parameter #1

    public static func + (lhs: Int, rhs: Int) -> Int
                       ^