error: Cannot inject fields from 'B' as this type does not exist
 --> tests/fail/circular_injection.rs:4:1
  |
4 | #[inject_fields(B)]
  | ^^^^^^^^^^^^^^^^^^^
  |
  = note: this error originates in the attribute macro `inject_fields` (in Nightly builds, run with -Z macro-backtrace for more info)

error: Circular injection chain detected: B already depends on A
  --> tests/fail/circular_injection.rs:10:1
   |
10 | #[inject_fields(A)]
   | ^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the attribute macro `inject_fields` (in Nightly builds, run with -Z macro-backtrace for more info)