Fix whitespace regression on forall+constraint type sig

src-literatetests/15-regressions.blt

@@ -680,3 +680,7 @@ a = \x -> x
 b = \ ~x -> x
 c = \ !x -> x
 d = \(~x) -> x
+
+#test type signature with forall and constraint
+{-# LANGUAGE RankNTypes #-}
+func :: forall b . Show b => b -> String

src/Language/Haskell/Brittany/Internal/Layouters/Type.hs

@@ -766,12 +766,15 @@ layoutTyVarBndrs = mapM $ \case
     return $ (lrdrNameToText lrdrName, Just $ d)
 #endif
 
+-- there is no specific reason this returns a list instead of a single
+-- BriDoc node.
 processTyVarBndrsSingleline
   :: [(Text, Maybe (ToBriDocM BriDocNumbered))] -> [ToBriDocM BriDocNumbered]
 processTyVarBndrsSingleline bndrDocs = bndrDocs >>= \case
-  (tname, Nothing) -> [docLit $ Text.pack " " <> tname]
+  (tname, Nothing) -> [docSeparator, docLit tname]
   (tname, Just doc) ->
-    [ docLit $ Text.pack " (" <> tname <> Text.pack " :: "
+    [ docSeparator
+    , docLit $ Text.pack "(" <> tname <> Text.pack " :: "
     , docForceSingleline $ doc
     , docLit $ Text.pack ")"
     ]