Stable sort for (data/newtype) instances

1 files changed, 17 insertions, 8 deletions

diff --git a/haddock-api/src/Haddock/Interface/AttachInstances.hs b/haddock-api/src/Haddock/Interface/AttachInstances.hs
index 6ef0ed19..d5b80888 100644
--- a/haddock-api/src/Haddock/Interface/AttachInstances.hs
+++ b/haddock-api/src/Haddock/Interface/AttachInstances.hs
@@ -179,19 +179,28 @@ findFixity iface ifaceMap instIfaceMap = \name ->
 -- Collecting and sorting instances
 --------------------------------------------------------------------------------
 
+-- | Stable name for stable comparisons. GHC's `Name` uses unstable
+-- ordering based on their `Unique`'s.
+newtype SName = SName Name
+
+instance Eq SName where
+  SName n1 == SName n2 = n1 `stableNameCmp` n2 == EQ
+
+instance Ord SName where
+  SName n1 `compare` SName n2 = n1 `stableNameCmp` n2
 
 -- | Simplified type for sorting types, ignoring qualification (not visible
 -- in Haddock output) and unifying special tycons with normal ones.
 -- For the benefit of the user (looks nice and predictable) and the
 -- tests (which prefer output to be deterministic).
-data SimpleType = SimpleType Name [SimpleType]
+data SimpleType = SimpleType SName [SimpleType]
                 | SimpleTyLit TyLit
                   deriving (Eq,Ord)
 
 
-instHead :: ([TyVar], [PredType], Class, [Type]) -> ([Int], Name, [SimpleType])
+instHead :: ([TyVar], [PredType], Class, [Type]) -> ([Int], SName, [SimpleType])
 instHead (_, _, cls, args)
-  = (map argCount args, className cls, map simplify args)
+  = (map argCount args, SName (className cls), map simplify args)
 
 argCount :: Type -> Int
 argCount (AppTy t _)     = argCount t + 1
@@ -202,12 +211,12 @@ argCount (CastTy t _)    = argCount t
 argCount _ = 0
 
 simplify :: Type -> SimpleType
-simplify (FunTy _ _ t1 t2)  = SimpleType funTyConName [simplify t1, simplify t2]
+simplify (FunTy _ _ t1 t2)  = SimpleType (SName funTyConName) [simplify t1, simplify t2]
 simplify (ForAllTy _ t) = simplify t
 simplify (AppTy t1 t2) = SimpleType s (ts ++ maybeToList (simplify_maybe t2))
   where (SimpleType s ts) = simplify t1
-simplify (TyVarTy v) = SimpleType (tyVarName v) []
-simplify (TyConApp tc ts) = SimpleType (tyConName tc)
+simplify (TyVarTy v) = SimpleType (SName (tyVarName v)) []
+simplify (TyConApp tc ts) = SimpleType (SName (tyConName tc))
                                        (mapMaybe simplify_maybe ts)
 simplify (LitTy l) = SimpleTyLit l
 simplify (CastTy ty _) = simplify ty
@@ -218,9 +227,9 @@ simplify_maybe (CoercionTy {}) = Nothing
 simplify_maybe ty              = Just (simplify ty)
 
 -- Used for sorting
-instFam :: FamInst -> ([Int], Name, [SimpleType], Int, SimpleType)
+instFam :: FamInst -> ([Int], SName, [SimpleType], Int, SimpleType)
 instFam FamInst { fi_fam = n, fi_tys = ts, fi_rhs = t }
-  = (map argCount ts, n, map simplify ts, argCount t, simplify t)
+  = (map argCount ts, SName n, map simplify ts, argCount t, simplify t)
 
 
 --------------------------------------------------------------------------------