Sample code to accompany blog post on Xcode extensions: implements an Xcode Source Editor extension to format Swift code.
This extension uses regular expressions to reformat malformed code marks (TODO, FIXME and MARK)
to be uppercased with a trailing colon,
enabling Xcode to recognize and add them to quick navigation links.
This formatting rule was inspired by one of the many rules provided by the
SwiftFormat project.
A fuller implementation like SwiftFormat's which also recognizes code marks inside /* */ comments
is left as an exercise for the reader 😇.