I am using the splendid command-line tool swiftformat (https://github.com/nicklockwood/SwiftFormat) to format my Swift code.
For my, the perfect integration point for this tool would be on Save in Xcode. In that way the formatting would not interrupt my editing, but I can see/check the changes done by the formatter, but never forget to format a file after editing.
I'd like to suggest a configuration option for Xcode that allows to configure it in such a way that, when I press save (cmd S) it saves the file and then runs a command line utility and reloads the file - or a capability for an Xcode source code editor extension to do such an operation.
One alternative could be to do it at build time which is possible to configure currently using a Build phase (https://github.com/nicklockwood/SwiftFormat#xcode-build-phase), but unfortunately, with this setup one loses all the undo history in Xcode.