I use Xcode 16.3. When I create a new project, it is automatically assigned to Swift 5. I would like to Swift 6. I know how to change for an existing project, but I would like to do it by default for every new project. How?
The Swift language version setting is actually specified as part of the project template. It is written in
/Applications/Xcode.app/Contents/Developer/Library/Xcode/Templates/Project Templates/Base/Base_ProjectSettings.xctemplate/TemplateInfo.plist
At the end of this file, there is a part that looks like this:
...
<key>Targets</key>
<array>
<dict>
<!-- Declare basic stuff that is true of all Swift targets, but mark this non-concrete so it won't cause actual creation of a target. -->
<key>Concrete</key>
<false/>
<key>SharedSettings</key>
<dict>
<key>SWIFT_VERSION</key>
<string>5.0</string>
</dict>
</dict>
</array>
...
Change that "5.0" and "6.0", then restart Xcode, and Voila!
Note that since this file is inside Xcode.app, you need sudo to change it. I opened the file in VSCode, then upon saving, VSCode prompts me to use sudo and enter my password. On the other hand, if I open the file in Xcode, Xcode just says it cannot be saved. I'm not a command line guy, but you could probably also cp the file to somewhere else, edit it, then sudo cp it back.