Tidy up the printing of single-predicate contexts

This covers things like
   Eq a => blah   and   (?x::Int) => blah
where there is just one predicate. Previously we used an ad-hoc
test to decide whether to parenthesise it, but acutally there is
a much simpler solution: just use the existing precedence mechamism.

This applies both to Type and HsType.

23 files changed, 97 insertions, 107 deletions

diff --git a/compiler/hsSyn/HsTypes.lhs b/compiler/hsSyn/HsTypes.lhs
index 7b7c7574b2..08a0eef498 100644
--- a/compiler/hsSyn/HsTypes.lhs
+++ b/compiler/hsSyn/HsTypes.lhs
@@ -35,7 +35,7 @@ module HsTypes (
         splitHsAppTys, hsTyGetAppHead_maybe, mkHsAppTys, mkHsOpTy,
 
         -- Printing
-        pprParendHsType, pprHsForAll, pprHsContext, pprHsContextNoArrow, ppr_hs_context,
+        pprParendHsType, pprHsForAll, pprHsContext, pprHsContextNoArrow, 
     ) where
 
 import {-# SOURCE #-} HsExpr ( HsSplice, pprUntypedSplice )
@@ -575,12 +575,8 @@ pprHsContext cxt = pprHsContextNoArrow cxt <+> darrow
 
 pprHsContextNoArrow :: (OutputableBndr name) => HsContext name -> SDoc
 pprHsContextNoArrow []         = empty
-pprHsContextNoArrow [L _ pred] = ppr pred
-pprHsContextNoArrow cxt        = ppr_hs_context cxt
-
-ppr_hs_context :: (OutputableBndr name) => HsContext name -> SDoc
-ppr_hs_context []  = empty
-ppr_hs_context cxt = parens (interpp'SP cxt)
+pprHsContextNoArrow [L _ pred] = ppr_mono_ty FunPrec pred
+pprHsContextNoArrow cxt        = parens (interpp'SP cxt)
 
 pprConDeclFields :: OutputableBndr name => [ConDeclField name] -> SDoc
 pprConDeclFields fields = braces (sep (punctuate comma (map ppr_fld fields)))
@@ -602,27 +598,12 @@ and the problem doesn't show up; but having the flag on a KindedTyVar
 seems like the Right Thing anyway.)
 
 \begin{code}
-pREC_TOP, pREC_FUN, pREC_OP, pREC_CON :: Int
-pREC_TOP = 0  -- type   in ParseIface.y
-pREC_FUN = 1  -- btype  in ParseIface.y
-              -- Used for LH arg of (->)
-pREC_OP  = 2  -- Used for arg of any infix operator
-              -- (we don't keep their fixities around)
-pREC_CON = 3  -- Used for arg of type applicn:
-              -- always parenthesise unless atomic
-
-maybeParen :: Int       -- Precedence of context
-           -> Int       -- Precedence of top-level operator
-           -> SDoc -> SDoc      -- Wrap in parens if (ctxt >= op)
-maybeParen ctxt_prec op_prec p | ctxt_prec >= op_prec = parens p
-                               | otherwise            = p
-        
--- printing works more-or-less as for Types
+-- Printing works more-or-less as for Types
 
 pprHsType, pprParendHsType :: (OutputableBndr name) => HsType name -> SDoc
 
-pprHsType ty       = getPprStyle $ \sty -> ppr_mono_ty pREC_TOP (prepare sty ty)
-pprParendHsType ty = ppr_mono_ty pREC_CON ty
+pprHsType ty       = getPprStyle $ \sty -> ppr_mono_ty TopPrec (prepare sty ty)
+pprParendHsType ty = ppr_mono_ty TyConPrec ty
 
 -- Before printing a type
 -- (a) Remove outermost HsParTy parens
@@ -632,15 +613,15 @@ prepare :: PprStyle -> HsType name -> HsType name
 prepare sty (HsParTy ty)          = prepare sty (unLoc ty)
 prepare _   ty                    = ty
 
-ppr_mono_lty :: (OutputableBndr name) => Int -> LHsType name -> SDoc
+ppr_mono_lty :: (OutputableBndr name) => TyPrec -> LHsType name -> SDoc
 ppr_mono_lty ctxt_prec ty = ppr_mono_ty ctxt_prec (unLoc ty)
 
-ppr_mono_ty :: (OutputableBndr name) => Int -> HsType name -> SDoc
+ppr_mono_ty :: (OutputableBndr name) => TyPrec -> HsType name -> SDoc
 ppr_mono_ty ctxt_prec (HsForAllTy exp tvs ctxt ty)
-  = maybeParen ctxt_prec pREC_FUN $
-    sep [pprHsForAll exp tvs ctxt, ppr_mono_lty pREC_TOP ty]
+  = maybeParen ctxt_prec FunPrec $
+    sep [pprHsForAll exp tvs ctxt, ppr_mono_lty TopPrec ty]
 
-ppr_mono_ty _    (HsBangTy b ty)     = ppr b <> ppr_mono_lty pREC_CON ty
+ppr_mono_ty _    (HsBangTy b ty)     = ppr b <> ppr_mono_lty TyConPrec ty
 ppr_mono_ty _    (HsQuasiQuoteTy qq) = ppr qq
 ppr_mono_ty _    (HsRecTy flds)      = pprConDeclFields flds
 ppr_mono_ty _    (HsTyVar name)      = pprPrefixOcc name
@@ -649,10 +630,10 @@ ppr_mono_ty _    (HsTupleTy con tys) = tupleParens std_con (interpp'SP tys)
   where std_con = case con of
                     HsUnboxedTuple -> UnboxedTuple
                     _              -> BoxedTuple
-ppr_mono_ty _    (HsKindSig ty kind) = parens (ppr_mono_lty pREC_TOP ty <+> dcolon <+> ppr kind)
-ppr_mono_ty _    (HsListTy ty)       = brackets (ppr_mono_lty pREC_TOP ty)
-ppr_mono_ty _    (HsPArrTy ty)       = paBrackets (ppr_mono_lty pREC_TOP ty)
-ppr_mono_ty prec (HsIParamTy n ty)   = maybeParen prec pREC_FUN (ppr n <+> dcolon <+> ppr_mono_lty pREC_TOP ty)
+ppr_mono_ty _    (HsKindSig ty kind) = parens (ppr_mono_lty TopPrec ty <+> dcolon <+> ppr kind)
+ppr_mono_ty _    (HsListTy ty)       = brackets (ppr_mono_lty TopPrec ty)
+ppr_mono_ty _    (HsPArrTy ty)       = paBrackets (ppr_mono_lty TopPrec ty)
+ppr_mono_ty prec (HsIParamTy n ty)   = maybeParen prec FunPrec (ppr n <+> dcolon <+> ppr_mono_lty TopPrec ty)
 ppr_mono_ty _    (HsSpliceTy s _)    = pprUntypedSplice s
 ppr_mono_ty _    (HsCoreTy ty)       = ppr ty
 ppr_mono_ty _    (HsExplicitListTy _ tys) = quote $ brackets (interpp'SP tys)
@@ -668,45 +649,45 @@ ppr_mono_ty ctxt_prec (HsWrapTy (WpKiApps _kis) ty)
   where
     go ctxt_prec [] ty = ppr_mono_ty ctxt_prec ty
     go ctxt_prec (ki:kis) ty
-      = maybeParen ctxt_prec pREC_CON $
-        hsep [ go pREC_FUN kis ty
+      = maybeParen ctxt_prec TyConPrec $
+        hsep [ go FunPrec kis ty
              , ptext (sLit "@") <> pprParendKind ki ]
 -}
 
 ppr_mono_ty ctxt_prec (HsEqTy ty1 ty2)
-  = maybeParen ctxt_prec pREC_OP $
-    ppr_mono_lty pREC_OP ty1 <+> char '~' <+> ppr_mono_lty pREC_OP ty2
+  = maybeParen ctxt_prec TyOpPrec $
+    ppr_mono_lty TyOpPrec ty1 <+> char '~' <+> ppr_mono_lty TyOpPrec ty2
 
 ppr_mono_ty ctxt_prec (HsAppTy fun_ty arg_ty)
-  = maybeParen ctxt_prec pREC_CON $
-    hsep [ppr_mono_lty pREC_FUN fun_ty, ppr_mono_lty pREC_CON arg_ty]
+  = maybeParen ctxt_prec TyConPrec $
+    hsep [ppr_mono_lty FunPrec fun_ty, ppr_mono_lty TyConPrec arg_ty]
 
 ppr_mono_ty ctxt_prec (HsOpTy ty1 (_wrapper, L _ op) ty2)
-  = maybeParen ctxt_prec pREC_OP $
-    sep [ ppr_mono_lty pREC_OP ty1
-        , sep [pprInfixOcc op, ppr_mono_lty pREC_OP ty2 ] ]
+  = maybeParen ctxt_prec TyOpPrec $
+    sep [ ppr_mono_lty TyOpPrec ty1
+        , sep [pprInfixOcc op, ppr_mono_lty TyOpPrec ty2 ] ]
     -- Don't print the wrapper (= kind applications)
     -- c.f. HsWrapTy
 
 ppr_mono_ty _         (HsParTy ty)
-  = parens (ppr_mono_lty pREC_TOP ty)
+  = parens (ppr_mono_lty TopPrec ty)
   -- Put the parens in where the user did
   -- But we still use the precedence stuff to add parens because
   --    toHsType doesn't put in any HsParTys, so we may still need them
 
 ppr_mono_ty ctxt_prec (HsDocTy ty doc) 
-  = maybeParen ctxt_prec pREC_OP $
-    ppr_mono_lty pREC_OP ty <+> ppr (unLoc doc)
+  = maybeParen ctxt_prec TyOpPrec $
+    ppr_mono_lty TyOpPrec ty <+> ppr (unLoc doc)
   -- we pretty print Haddock comments on types as if they were
   -- postfix operators
 
 --------------------------
-ppr_fun_ty :: (OutputableBndr name) => Int -> LHsType name -> LHsType name -> SDoc
+ppr_fun_ty :: (OutputableBndr name) => TyPrec -> LHsType name -> LHsType name -> SDoc
 ppr_fun_ty ctxt_prec ty1 ty2
-  = let p1 = ppr_mono_lty pREC_FUN ty1
-        p2 = ppr_mono_lty pREC_TOP ty2
+  = let p1 = ppr_mono_lty FunPrec ty1
+        p2 = ppr_mono_lty TopPrec ty2
     in
-    maybeParen ctxt_prec pREC_FUN $
+    maybeParen ctxt_prec FunPrec $
     sep [p1, ptext (sLit "->") <+> p2]
 
 --------------------------
diff --git a/compiler/types/Type.lhs b/compiler/types/Type.lhs
index 0e93c9699f..808216f2ef 100644
--- a/compiler/types/Type.lhs
+++ b/compiler/types/Type.lhs
@@ -51,7 +51,7 @@ module Type (
         isDictLikeTy,
         mkEqPred, mkCoerciblePred, mkPrimEqPred, mkReprPrimEqPred,
         mkClassPred,
-        noParenPred, isClassPred, isEqPred,
+        isClassPred, isEqPred,
         isIPPred, isIPPred_maybe, isIPTyCon, isIPClass,
 
         -- Deconstructing predicate types
@@ -132,6 +132,7 @@ module Type (
         pprTvBndr, pprTvBndrs, pprForAll, pprUserForAll, pprSigmaType,
         pprTheta, pprThetaArrowTy, pprClassPred,
         pprKind, pprParendKind, pprSourceTyCon,
+        TyPrec(..), maybeParen,
 
         -- * Tidying type related things up for printing
         tidyType,      tidyTypes,
@@ -833,13 +834,6 @@ applyTysD doc orig_fun_ty arg_tys
 Predicates on PredType
 
 \begin{code}
-noParenPred :: PredType -> Bool
--- A predicate that can appear without parens before a "=>"
---       C a => a -> a
---       a~b => a -> b
--- But   (?x::Int) => Int -> Int
-noParenPred p = not (isIPPred p) && isClassPred p || isEqPred p
-
 isPredTy :: Type -> Bool
   -- NB: isPredTy is used when printing types, which can happen in debug printing
   --     during type checking of not-fully-zonked types.  So it's not cool to say
diff --git a/compiler/types/Type.lhs-boot b/compiler/types/Type.lhs-boot
index c2d2dec093..ff9db3e28c 100644
--- a/compiler/types/Type.lhs-boot
+++ b/compiler/types/Type.lhs-boot
@@ -3,7 +3,6 @@ module Type where
 import {-# SOURCE #-} TypeRep( Type, Kind )
 import Var
 
-noParenPred :: Type -> Bool
 isPredTy :: Type -> Bool
 
 typeKind :: Type -> Kind
diff --git a/compiler/types/TypeRep.lhs b/compiler/types/TypeRep.lhs
index c93a653310..c8b20e8d93 100644
--- a/compiler/types/TypeRep.lhs
+++ b/compiler/types/TypeRep.lhs
@@ -66,7 +66,7 @@ module TypeRep (
 
 import {-# SOURCE #-} DataCon( dataConTyCon )
 import ConLike ( ConLike(..) )
-import {-# SOURCE #-} Type( noParenPred, isPredTy ) -- Transitively pulls in a LOT of stuff, better to break the loop
+import {-# SOURCE #-} Type( isPredTy ) -- Transitively pulls in a LOT of stuff, better to break the loop
 
 -- friends:
 import Var
@@ -491,11 +491,29 @@ defined to use this.  @pprParendType@ is the same, except it puts
 parens around the type, except for the atomic cases.  @pprParendType@
 works just by setting the initial context precedence very high.
 
+Note [Precedence in types]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+We don't keep the fixity of type operators in the operator. So the pretty printer
+operates the following precedene structre:
+   Type constructor application   binds more tightly than
+   Oerator applications           which bind more tightly than
+   Function arrow
+
+So we might see  a :+: T b -> c
+meaning          (a :+: (T b)) -> c
+
+Maybe operator applications should bind a bit less tightly?
+
+Anyway, that's the current story, and it is used consistently for Type and HsType
+
 \begin{code}
-data TyPrec = TopPrec         -- No parens
-            | FunPrec         -- Function args; no parens for tycon apps
-            | TyConPrec       -- Tycon args; no parens for atomic
-            deriving( Eq, Ord )
+data TyPrec   -- See Note [Prededence in types]
+
+  = TopPrec         -- No parens
+  | FunPrec         -- Function args; no parens for tycon apps
+  | TyOpPrec        -- Infix operator
+  | TyConPrec       -- Tycon args; no parens for atomic
+  deriving( Eq, Ord )
 
 maybeParen :: TyPrec -> TyPrec -> SDoc -> SDoc
 maybeParen ctxt_prec inner_prec pretty
@@ -524,10 +542,9 @@ pprTheta :: ThetaType -> SDoc
 pprTheta theta  = parens (sep (punctuate comma (map (ppr_type TopPrec) theta)))
 
 pprThetaArrowTy :: ThetaType -> SDoc
-pprThetaArrowTy []      = empty
-pprThetaArrowTy [pred]
-      | noParenPred pred = ppr_type TopPrec pred <+> darrow
-pprThetaArrowTy preds   = parens (fsep (punctuate comma (map (ppr_type TopPrec) preds)))
+pprThetaArrowTy []     = empty
+pprThetaArrowTy [pred] = ppr_type FunPrec pred <+> darrow
+pprThetaArrowTy preds  = parens (fsep (punctuate comma (map (ppr_type TopPrec) preds)))
                             <+> darrow
     -- Notice 'fsep' here rather that 'sep', so that
     -- type contexts don't get displayed in a giant column
@@ -563,13 +580,7 @@ instance Outputable TyLit where
 
 ppr_type :: TyPrec -> Type -> SDoc
 ppr_type _ (TyVarTy tv)	      = ppr_tvar tv
-
-ppr_type _ (TyConApp tc [LitTy (StrTyLit n),ty])
-  | tc `hasKey` ipClassNameKey
-  = char '?' <> ftext n <> ptext (sLit "::") <> ppr_type TopPrec ty
-
 ppr_type p (TyConApp tc tys)  = pprTyTcApp p tc tys
-
 ppr_type p (LitTy l)          = ppr_tylit p l
 ppr_type p ty@(ForAllTy {})   = ppr_forall_type p ty
 
@@ -696,6 +707,11 @@ pprTyTcApp :: TyPrec -> TyCon -> [Type] -> SDoc
 -- Used for types only; so that we can make a
 -- special case for type-level lists
 pprTyTcApp p tc tys
+  | tc `hasKey` ipClassNameKey
+  , [LitTy (StrTyLit n),ty] <- tys
+  = maybeParen p FunPrec $
+    char '?' <> ftext n <> ptext (sLit "::") <> ppr_type TopPrec ty
+
   | tc `hasKey` consDataConKey
   , [_kind,ty1,ty2] <- tys
   = sdocWithDynFlags $ \dflags ->
@@ -788,8 +804,8 @@ pprTyList p ty1 ty2
 ----------------
 pprInfixApp :: TyPrec -> (TyPrec -> a -> SDoc) -> SDoc -> a -> a -> SDoc
 pprInfixApp p pp pp_tc ty1 ty2
-  = maybeParen p FunPrec $
-    sep [pp FunPrec ty1, pprInfixVar True pp_tc <+> pp FunPrec ty2]
+  = maybeParen p TyOpPrec $
+    sep [pp TyOpPrec ty1, pprInfixVar True pp_tc <+> pp TyOpPrec ty2]
 
 pprPrefixApp :: TyPrec -> SDoc -> [SDoc] -> SDoc
 pprPrefixApp p pp_fun pp_tys 
diff --git a/testsuite/tests/deSugar/should_compile/T2431.stderr b/testsuite/tests/deSugar/should_compile/T2431.stderr
index dbafaedf82..c40b603d3f 100644
--- a/testsuite/tests/deSugar/should_compile/T2431.stderr
+++ b/testsuite/tests/deSugar/should_compile/T2431.stderr
@@ -13,7 +13,7 @@ T2431.$WRefl [InlPrag=INLINE] :: forall a. a T2431.:~: a
 T2431.$WRefl = \ (@ a) -> T2431.Refl @ a @ a @~ <a>_N
 
 T2431.absurd
-  :: forall a. (GHC.Types.Int T2431.:~: GHC.Types.Bool) -> a
+  :: forall a. GHC.Types.Int T2431.:~: GHC.Types.Bool -> a
 [GblId, Arity=1, Caf=NoCafRefs, Str=DmdType <L,U>b]
 T2431.absurd =
   \ (@ a) (x :: GHC.Types.Int T2431.:~: GHC.Types.Bool) ->
diff --git a/testsuite/tests/ghci/scripts/Defer02.stderr b/testsuite/tests/ghci/scripts/Defer02.stderr
index ed36a3eb3c..7635c8f804 100644
--- a/testsuite/tests/ghci/scripts/Defer02.stderr
+++ b/testsuite/tests/ghci/scripts/Defer02.stderr
@@ -84,13 +84,13 @@
       the type signature for k :: Int ~ Bool => Int -> Bool
     In the ambiguity check for: Int ~ Bool => Int -> Bool
     To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
-    In the type signature for ‘k’: k :: Int ~ Bool => Int -> Bool
+    In the type signature for ‘k’: k :: (Int ~ Bool) => Int -> Bool
 
 ../../typecheck/should_run/Defer01.hs:45:6: Warning:
     Couldn't match expected type ‘Bool’ with actual type ‘Int’
     In the ambiguity check for: Int ~ Bool => Int -> Bool
     To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
-    In the type signature for ‘k’: k :: Int ~ Bool => Int -> Bool
+    In the type signature for ‘k’: k :: (Int ~ Bool) => Int -> Bool
 
 ../../typecheck/should_run/Defer01.hs:45:6: Warning:
     Couldn't match type ‘Int’ with ‘Bool’
diff --git a/testsuite/tests/ghci/scripts/T2766.stdout b/testsuite/tests/ghci/scripts/T2766.stdout
index f8ee42ff6a..5bcbd9e75e 100644
--- a/testsuite/tests/ghci/scripts/T2766.stdout
+++ b/testsuite/tests/ghci/scripts/T2766.stdout
@@ -1,3 +1,3 @@
 first :: Arrow to => b `to` c -> (b, d) `to` (c, d)
   :: Arrow to => to b c -> to (b, d) (c, d)
-first :: b~>c -> (b, d)~>(c, d) :: (b ~> c) -> (b, d) ~> (c, d)
+first :: b~>c -> (b, d)~>(c, d) :: b ~> c -> (b, d) ~> (c, d)
diff --git a/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr b/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr
index fa92d3dd92..7ce82d0067 100644
--- a/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr
+++ b/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr
@@ -85,7 +85,7 @@ newtype N5 a b
 newtype N6 a b =  docs on the constructor only N6 {n6 :: a b}
 <document comment>
 newtype N7 a b =  The 'N7' constructor N7 {n7 :: a b}
-class D a => C a where
+class (D a) => C a where
   a :: IO a
   b :: [a]
   c :: a
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr
index 6d803bb440..2bb1a178e0 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr
@@ -1,7 +1,7 @@
 
 ==================== Parser ====================
 module ShouldCompile where
-test :: Eq a => [a]  doc1  -> [a]  doc2  -> [a]  doc3
+test :: (Eq a) => [a]  doc1  -> [a]  doc2  -> [a]  doc3
 test xs ys = xs
 
 
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr
index 3e3cb12d10..4a57879c5c 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr
@@ -1,7 +1,7 @@
 
 ==================== Parser ====================
 module ShouldCompile where
-test :: Eq a => [a]  doc1  -> forall b. [b]  doc2  -> [a]  doc3
+test :: (Eq a) => [a]  doc1  -> forall b. [b]  doc2  -> [a]  doc3
 test xs ys = xs
 
 
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr
index 10e88d2bfc..d1cb709c55 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr
@@ -3,8 +3,8 @@
 module ShouldCompile where
 test ::
   [a]  doc1 
-  -> forall b. Ord b =>
-     [b]  doc2  -> forall c. Num c => [c]  doc3 -> [a]
+  -> forall b. (Ord b) =>
+     [b]  doc2  -> forall c. (Num c) => [c]  doc3 -> [a]
 test xs ys zs = xs
 
 
diff --git a/testsuite/tests/indexed-types/should_fail/NoMatchErr.stderr b/testsuite/tests/indexed-types/should_fail/NoMatchErr.stderr
index 1ff540979b..d3193d5f30 100644
--- a/testsuite/tests/indexed-types/should_fail/NoMatchErr.stderr
+++ b/testsuite/tests/indexed-types/should_fail/NoMatchErr.stderr
@@ -11,4 +11,4 @@ NoMatchErr.hs:19:7:
     In the ambiguity check for:
       forall d a. Fun d => Memo d a -> Memo d a
     To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
-    In the type signature for ‘f’: f :: Fun d => Memo d a -> Memo d a
+    In the type signature for ‘f’: f :: (Fun d) => Memo d a -> Memo d a
diff --git a/testsuite/tests/indexed-types/should_fail/T1900.stderr b/testsuite/tests/indexed-types/should_fail/T1900.stderr
index 435d5e8312..d44b4ed210 100644
--- a/testsuite/tests/indexed-types/should_fail/T1900.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T1900.stderr
@@ -11,4 +11,4 @@ T1900.hs:13:10:
     In the ambiguity check for: forall s. Bug s => Depend s -> Bool
     To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
     In the type signature for ‘check’:
-      check :: Bug s => Depend s -> Bool
+      check :: (Bug s) => Depend s -> Bool
diff --git a/testsuite/tests/perf/compiler/T5837.stderr b/testsuite/tests/perf/compiler/T5837.stderr
index 2d2907d3ae..5cee13dd1d 100644
--- a/testsuite/tests/perf/compiler/T5837.stderr
+++ b/testsuite/tests/perf/compiler/T5837.stderr
@@ -158,4 +158,4 @@ T5837.hs:8:6:
                                                                                                                                                           (TF
                                                                                                                                                              a)))))))))))))))))))))))))))))))))))))))))))))))))
     In the ambiguity check for: forall a. a ~ TF (a, Int) => Int
-    In the type signature for ‘t’: t :: a ~ TF (a, Int) => Int
+    In the type signature for ‘t’: t :: (a ~ TF (a, Int)) => Int
diff --git a/testsuite/tests/polykinds/T7278.stderr b/testsuite/tests/polykinds/T7278.stderr
index f24f9b2aad..3d615c12f7 100644
--- a/testsuite/tests/polykinds/T7278.stderr
+++ b/testsuite/tests/polykinds/T7278.stderr
@@ -2,4 +2,4 @@
 T7278.hs:8:43:
     ‘t’ is applied to too many type arguments
     In the type signature for ‘f’:
-      f :: C (t :: k) (TF t) => TF t p1 p0 -> t p1 p0
+      f :: (C (t :: k) (TF t)) => TF t p1 p0 -> t p1 p0
diff --git a/testsuite/tests/typecheck/should_fail/ContextStack2.stderr b/testsuite/tests/typecheck/should_fail/ContextStack2.stderr
index a9c5cbc13a..e99e4c4264 100644
--- a/testsuite/tests/typecheck/should_fail/ContextStack2.stderr
+++ b/testsuite/tests/typecheck/should_fail/ContextStack2.stderr
@@ -6,4 +6,4 @@ ContextStack2.hs:8:6:
        TF (TF (TF (TF (TF (TF (TF (TF (TF (TF (TF Int)))))))))))
       ~ TF (TF (TF (TF (TF (TF (TF (TF (TF (TF a)))))))))
     In the ambiguity check for: forall a. a ~ TF (a, Int) => Int
-    In the type signature for ‘t’: t :: a ~ TF (a, Int) => Int
+    In the type signature for ‘t’: t :: (a ~ TF (a, Int)) => Int
diff --git a/testsuite/tests/typecheck/should_fail/T7609.stderr b/testsuite/tests/typecheck/should_fail/T7609.stderr
index 1b904bbec7..b02dbe20f8 100644
--- a/testsuite/tests/typecheck/should_fail/T7609.stderr
+++ b/testsuite/tests/typecheck/should_fail/T7609.stderr
@@ -1,10 +1,10 @@
-

-T7609.hs:7:16:

-    Expecting one more argument to ‘Maybe’

-    The second argument of a tuple should have kind ‘*’,

-      but ‘Maybe’ has kind ‘* -> *’

-    In the type signature for ‘f’: f :: (a `X` a, Maybe)

-

-T7609.hs:10:7:

-    Expected a constraint, but ‘a `X` a’ has kind ‘*’

-    In the type signature for ‘g’: g :: a `X` a => Maybe

+
+T7609.hs:7:16:
+    Expecting one more argument to ‘Maybe’
+    The second argument of a tuple should have kind ‘*’,
+      but ‘Maybe’ has kind ‘* -> *’
+    In the type signature for ‘f’: f :: (a `X` a, Maybe)
+
+T7609.hs:10:7:
+    Expected a constraint, but ‘a `X` a’ has kind ‘*’
+    In the type signature for ‘g’: g :: (a `X` a) => Maybe
diff --git a/testsuite/tests/typecheck/should_fail/T7778.stderr b/testsuite/tests/typecheck/should_fail/T7778.stderr
index 714e2a6e27..136625af75 100644
--- a/testsuite/tests/typecheck/should_fail/T7778.stderr
+++ b/testsuite/tests/typecheck/should_fail/T7778.stderr
@@ -2,4 +2,4 @@
 T7778.hs:3:19:
     Expecting one more argument to ‘Num’
     Expected a type, but ‘Num’ has kind ‘* -> Constraint’
-    In the type signature for ‘v’: v :: (Num Int => Num) () => ()
+    In the type signature for ‘v’: v :: ((Num Int => Num) ()) => ()
diff --git a/testsuite/tests/typecheck/should_fail/T8392a.stderr b/testsuite/tests/typecheck/should_fail/T8392a.stderr
index ae7fc2ca6a..ed33600a1e 100644
--- a/testsuite/tests/typecheck/should_fail/T8392a.stderr
+++ b/testsuite/tests/typecheck/should_fail/T8392a.stderr
@@ -4,4 +4,4 @@ T8392a.hs:6:8:
     Inaccessible code in
       the type signature for foo :: Int ~ Bool => a -> a
     In the ambiguity check for: forall a. Int ~ Bool => a -> a
-    In the type signature for ‘foo’: foo :: Int ~ Bool => a -> a
+    In the type signature for ‘foo’: foo :: (Int ~ Bool) => a -> a
diff --git a/testsuite/tests/typecheck/should_fail/T8806.stderr b/testsuite/tests/typecheck/should_fail/T8806.stderr
index 0a5a3d731f..5d50c4ec10 100644
--- a/testsuite/tests/typecheck/should_fail/T8806.stderr
+++ b/testsuite/tests/typecheck/should_fail/T8806.stderr
@@ -5,4 +5,4 @@ T8806.hs:5:6:
 
 T8806.hs:8:7:
     Expected a constraint, but ‘Int’ has kind ‘*’
-    In the type signature for ‘g’: g :: Int => Show a => Int
+    In the type signature for ‘g’: g :: (Int => Show a) => Int
diff --git a/testsuite/tests/typecheck/should_fail/tcfail032.stderr b/testsuite/tests/typecheck/should_fail/tcfail032.stderr
index 954a6fd5ec..4d41c103da 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail032.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail032.stderr
@@ -8,5 +8,5 @@ tcfail032.hs:14:8:
     Relevant bindings include
       x :: t (bound at tcfail032.hs:14:3)
       f :: t -> a -> Int (bound at tcfail032.hs:14:1)
-    In the expression: (x :: Eq a => a -> Int)
-    In an equation for ‘f’: f x = (x :: Eq a => a -> Int)
+    In the expression: (x :: (Eq a) => a -> Int)
+    In an equation for ‘f’: f x = (x :: (Eq a) => a -> Int)
diff --git a/testsuite/tests/typecheck/should_fail/tcfail058.stderr b/testsuite/tests/typecheck/should_fail/tcfail058.stderr
index 101a6a07d2..74db76afd8 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail058.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail058.stderr
@@ -2,4 +2,4 @@
 tcfail058.hs:6:7:
     Expecting one more argument to ‘Array a’
     Expected a constraint, but ‘Array a’ has kind ‘* -> *’
-    In the type signature for ‘f’: f :: Array a => a -> b
+    In the type signature for ‘f’: f :: (Array a) => a -> b
diff --git a/testsuite/tests/typecheck/should_fail/tcfail215.stderr b/testsuite/tests/typecheck/should_fail/tcfail215.stderr
index d7fa2d84f7..2157561827 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail215.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail215.stderr
@@ -1,4 +1,4 @@
 
 tcfail215.hs:8:15:
     Expecting a lifted type, but ‘Int#’ is unlifted
-    In the type signature for ‘foo’: foo :: ?x :: Int# => Int
+    In the type signature for ‘foo’: foo :: (?x :: Int#) => Int