I didn’t know binaries could embed LLDB-specific bytecode for formatting custom data types nicely in the debugger, as shown in this swift-collections PR: https://github.com/apple/swift-collections/pull/607. The code also uses fancy new Swift features to place the bytecode in a specific linker section:
@section(".lldbformatters")
@used
let __BasicContainers___RigidArray______formatter: (UInt8, UInt8, …, UInt8) = …