De-duplicate displayContext and displayExceptionContext

The former was unused except for one module where it was essentially
re-defining displayExceptionContext.

Moreover, this commit extends the fix from
bfe600f5 to displayExceptionContext too,
which was missing.

libraries/ghc-internal/src/GHC/Internal/Exception/Context.hs

@@ -34,7 +34,8 @@ module GHC.Internal.Exception.Context
     , ExceptionAnnotation(..)
     ) where
 
-import GHC.Internal.Base ((++), return, String, Maybe(..), Semigroup(..), Monoid(..))
+import GHC.Internal.Data.OldList (intersperse)
+import GHC.Internal.Base (($), map, (++), return, String, Maybe(..), Semigroup(..), Monoid(..))
 import GHC.Internal.Show (Show(..))
 import GHC.Internal.Data.Typeable.Internal (Typeable, typeRep, eqTypeRep)
 import GHC.Internal.Data.Type.Equality ( (:~~:)(HRefl) )
@@ -92,10 +93,9 @@ mergeExceptionContext (ExceptionContext a) (ExceptionContext b) = ExceptionConte
 --
 -- @since base-4.20.0.0
 displayExceptionContext :: ExceptionContext -> String
-displayExceptionContext (ExceptionContext anns0) = go anns0
+displayExceptionContext (ExceptionContext anns0) = mconcat $ intersperse "\n" $ map go anns0
   where
-    go (SomeExceptionAnnotation ann : anns) = displayExceptionAnnotation ann ++ "\n" ++ go anns
-    go [] = "\n"
+    go (SomeExceptionAnnotation ann) = displayExceptionAnnotation ann
 
 data SomeExceptionAnnotation = forall a. ExceptionAnnotation a => SomeExceptionAnnotation a
 

libraries/ghc-internal/src/GHC/Internal/Exception/Type.hs

@@ -49,7 +49,7 @@ module GHC.Internal.Exception.Type
        , underflowException
        ) where
 
-import GHC.Internal.Data.OldList (intersperse, lines, unlines, null)
+import GHC.Internal.Data.OldList (lines, unlines, null)
 import GHC.Internal.Data.Maybe
 import GHC.Internal.Data.Typeable (Typeable, TypeRep, cast)
 import qualified GHC.Internal.Data.Typeable as Typeable
@@ -252,7 +252,7 @@ instance Exception SomeException where
 -- @since base-4.21
 displayExceptionWithInfo :: SomeException -> String
 displayExceptionWithInfo (SomeException e) =
-    case displayContext ?exceptionContext of
+    case displayExceptionContext ?exceptionContext of
       "" -> msg
       dc -> msg ++ "\n\n" ++ dc
     where
@@ -268,11 +268,6 @@ displayExceptionWithInfo (SomeException e) =
             tyMsg = Typeable.tyConPackage tyCon ++ ":" ++ Typeable.tyConModule tyCon ++ "." ++ Typeable.tyConName tyCon
             tyCon = Typeable.typeRepTyCon rep
 
-displayContext :: ExceptionContext -> String
-displayContext (ExceptionContext anns0) = mconcat $ intersperse "\n" $ map go anns0
-  where
-    go (SomeExceptionAnnotation ann) = displayExceptionAnnotation ann
-
 newtype NoBacktrace e = NoBacktrace e
     deriving (Show)