Merge pull request #4830 from hvr/pr/issue4808

RFC: Potential fix for #4808

Cabal/Distribution/Types/GenericPackageDescription.hs

@@ -159,7 +159,7 @@ dispFlagAssignment = Disp.hsep . map (Disp.text . showFlagValue)
 
 -- | Parses a flag assignment.
 parsecFlagAssignment :: ParsecParser FlagAssignment
-parsecFlagAssignment = P.sepBy1 (onFlag <|> offFlag) P.skipSpaces1
+parsecFlagAssignment = P.sepBy (onFlag <|> offFlag) P.skipSpaces1
   where
     onFlag = do
         P.optional (P.char '+')
@@ -172,7 +172,7 @@ parsecFlagAssignment = P.sepBy1 (onFlag <|> offFlag) P.skipSpaces1
 
 -- | Parses a flag assignment.
 parseFlagAssignment :: Parse.ReadP r FlagAssignment
-parseFlagAssignment = Parse.sepBy1 parseFlagValue Parse.skipSpaces1
+parseFlagAssignment = Parse.sepBy parseFlagValue Parse.skipSpaces1
   where
     parseFlagValue =
           (do Parse.optional (Parse.char '+')