Believe it or not, Swift, blindly repeating your obtuse error messages does not help.
What it’s trying but as usual failing miserably to tell me is that Dictionary doesn’t have an initialiser that takes key: value pairs (my mistake for writing straight-forward, Python-like code). You have to use the dictionary literal syntax instead:
Foo.swift:75:49: error: expression was too complex to be solved in reasonable time; consider breaking up the expression into distinct sub-expressions
let componentsOfPotentialInterest = [(Calendar.Component, ((Int) -> String))](