Swift attached macro causes circular reference when used with inner type extension

[edudnyk]

Description

Taking equatable extension macro implementation from Swift Macro Examples in swift-syntax repository, and having the following code:

@equatable
struct Pet {
  struct Dog {}

  let name: String
}

extension Pet.Dog {}

the compiler throws “circular reference resolving attached macro ‘equatable’” error (see screenshot).

Steps to Reproduce

1. Clone https://github.com/edudnyk/swift-syntax.git
2. Checkout branch attached-macro-bugreport.
3. Open Package.swift in Xcode.
4. Open Examples/Sources/MacroExamples/Playground/ExtensionMacrosPlayground.swift
5. Build the MacroExamplesPlayground target.

Apple Feedback ID: FB14887944

[ahoppen]

Synced to Apple’s issue tracker as rdar://134489854

[ahoppen]

Moving to the compiler repo because this is about error messages generated by the compiler.