ちなみに InternalImportsByDefault は Language Steering Group で方針転換があって Swift 6 じゃなくて Swift 7 に見送られたみたいです． https://github.com/apple/swift/pull/73149

[6.0] Sema: Remove internal imports by default from Swift 6 by xymu...

The language steering group has decided to revert their previous decision and remove this feature from Swift 6. Scope: Bare import statements in Swift 6. Risk: This will be source breaking for earl...