Swift Macros: Adding an enum case with an associated value produces incorrect results

Reproduced in Xcode versions 15.0.1 and 15.1 beta 3.

If a Macro adds an enum case with an associated value, other cases are transformed at runtime. In the example below, the case foo is translated into the Macro-generated case bar(false).

There is lots of other strange behavior, such as:

• Case declarations in the same file as the enum are not transformed. For example, in the code above, a function written in SimpleEnum.swift can produce SimpleEnum.foo, whereas functions in other files cannot (the declarations are transformed).
• Manually-defined cases with associated values are not transformed. For example, a manually-defined case foobar(Bool) can be declared and used normally everywhere.
• Additional enum cases without associated values get transformed to different cases. For example, if SimpleEnum has manual cases foo, foobar, and foobarfoo, and a Macro-generated bar(Bool), these transformations take place:
  • foo -> bar(false)
  • foobar -> bar(true)
  • foobarfoo -> foo
  • etc.
• Not all associated value types in the Macro-generated case are treated the same. String associated values seems to work properly. Int yields incrementing transformations (e.g. foo -> bar(0), foobar -> bar(1), foobarfoo -> bar(2))

Radar: FB13417290