Put the generic-default type in the Class

This is an internal GHC refactoring ticket. Consider

{-# LANGUAGE DefaultSignatures #-}
class C a where
  op :: a -> a -> Bool
  default op :: Ord a => a -> a -> Bool
  op x y = x < y

The Class object for C has a ClassOpItem that specifies

• the name op
• the type of the method a -> a -> Bool
• that op has a generic-default signature

BUT it does not contain the actual signature Ord a => a -> a -> Bool. That's really wrong; it is certainly part of the definition of the class, and we should print it out when we say :info C in ghci.

Instead this type is kept solely in the top-level generic-default Id binding. But that means that default-method Ids and generic-default method Ids are treated differently; see gen_dm_ids in tcTyClDecl1 in TcTyClsDecls, and mkDefaultMethodIds in TcTyDecls.

We should treat them uniformly. I know how but have too much in flight to do it immediately.

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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