Swift migration assistant

If you open your project with Xcode 9 for the first time, you will see a migration opportunity item in the Issue Navigator; click on it to activate a sheet asking you if you'd like to migrate. You can be reminded later or invoke the migrator manually from the menu—Edit | Convert | To Current Swift Syntax…

You will be given a list of targets to migrate. Only those targets that contain Swift code will be selected.

There is only one migration workflow this year, although there is a choice between two kinds of @objc inference:

• Minimize inference: Add an @objc attribute to your code only where it is needed based on static inference. After using this option, you need to follow the manual steps.
• Match Swift 3 behavior: Add an @objc attribute to your code anywhere it would be implicitly inferred by the compiler. This option does not change the size of your binary as it adds explicit @objc attributes everywhere.

Clicking on Next will bring up the Generate Preview sheet and a migration build will be initiated by the assistant to get source changes. Once this is completed, you will be shown all the changes that will be applied when you click on Save. This will also change the Swift language version build setting for the migrated targets to Swift 4.

You may find some issues while processing the targets during the migration process. You can check the log for these errors by switching to report navigator and converting the entry that was added.