Fix-it is a feature of the source editor that checks for syntax errors as you write code. Any issues are marked with a red underline or a caret at the position of the error. An error icon also appears in the gutter. Clicking the icon in the gutter displays a message describing the possible error and, in many cases, offers to repair it automatically.
Important: To use Fix-it, you must build the target with the LLVM or Swift compiler and the indexing of your project must be complete. Fix-it works with Swift, C, Objective-C, and Objective-C++.