reduction stack overflow for non-existent instances

[andy-morris]

extensible [d|
    data A = A B        deriving Eq
    data B = B A | Stop deriving Eq
  |]

data T
extendA "A" [] [t|T|] defaultExtA
extendB "B" [] [t|T|] defaultExtB

>>> Stop < Stop
<interactive>:1:1: error:
    • Reduction stack overflow; size = 201
      When simplifying the following type: Eq (B' ext0)
      Use -freduction-depth=0 to disable this check
      (any upper bound you could choose might fail unpredictably with
       minor updates to GHC, so disabling the check is recommended if
       you're sure that type checking should terminate)
    • In the expression: Stop < Stop
      In an equation for ‘it’: it = Stop < Stop

(should say "No instance for (Ord B)")

>>> :i A' B'
type role A' nominal
data A' ext = A' (B' ext) !(XA ext) | AX !(AX ext)
        -- Defined at A.hs:9:1
instance (Eq (AX ext), Eq (B' ext), Eq (XA ext)) => Eq (A' ext)
  --                   ↑↑↑↑↑↑↑↑↑↑↑
  -- Defined at A.hs:9:1
type role B' nominal
data B' ext
  = B' (A' ext) !(XB ext) | Stop' !(XStop ext) | BX !(BX ext)
        -- Defined at A.hs:9:1
instance (Eq (A' ext), Eq (BX ext), Eq (XB ext), Eq (XStop ext)) => Eq (B' ext)
  --      ↑↑↑↑↑↑↑↑↑↑↑
  -- Defined at A.hs:9:1

the problem is caused by Eq (A' ext) having a superclass Eq (B' ext) and vice versa, instead of using AAll/BAll