Suggestions based on initial label match

[dabrahams]

/Users/dave/src/val/Tests/ValTests/Utils/AnnotatedValFileTest.swift:94:45: error: value of type '[TestAnnotation : Diagnostic]' has no member 'indexForKey'
        if let i = diagnosticsByExpectation.indexForKey(a) {
                   ~~~~~~~~~~~~~~~~~~~~~~~~ ^~~~~~~~~~~

diagnosticsByExpectation is a Dictionary. It would be nice if the compiler suggested "did you mean: index(forKey: a)" with a fixit.