Marker Extension

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 😇.