Moved 'skipSpaces1' into a central location.

Cabal/Distribution/Compat/ReadP.hs

@@ -44,6 +44,7 @@ module Distribution.Compat.ReadP
   munch,      -- :: (Char -> Bool) -> ReadP String
   munch1,     -- :: (Char -> Bool) -> ReadP String
   skipSpaces, -- :: ReadP ()
+  skipSpaces1,-- :: ReadP ()
   choice,     -- :: [ReadP a] -> ReadP a
   count,      -- :: Int -> ReadP a -> ReadP [a]
   between,    -- :: ReadP open -> ReadP close -> ReadP a -> ReadP a
@@ -297,6 +298,11 @@ skipSpaces =
   skip (c:s) | isSpace c = do _ <- get; skip s
   skip _                 = do return ()
 
+skipSpaces1 :: ReadP r ()
+-- ^ Like 'skipSpaces' but succeeds only if there is at least one
+-- whitespace character to skip.
+skipSpaces1 = satisfy isSpace >> skipSpaces
+
 count :: Int -> ReadP r a -> ReadP r [a]
 -- ^ @ count n p @ parses @n@ occurrences of @p@ in sequence. A list of
 --   results is returned.

cabal-install/Distribution/Client/Targets.hs

@@ -766,19 +766,19 @@ instance Text UserConstraint where
     where
       parseConstraint pkgname =
             ((parse >>= return . UserConstraintVersion pkgname)
-        +++ (do skipSpaces1
+        +++ (do Parse.skipSpaces1
                 _ <- Parse.string "installed"
                 return (UserConstraintInstalled pkgname))
-        +++ (do skipSpaces1
+        +++ (do Parse.skipSpaces1
                 _ <- Parse.string "source"
                 return (UserConstraintSource pkgname))
-        +++ (do skipSpaces1
+        +++ (do Parse.skipSpaces1
                 _ <- Parse.string "test"
                 return (UserConstraintStanzas pkgname [TestStanzas]))
-        +++ (do skipSpaces1
+        +++ (do Parse.skipSpaces1
                 _ <- Parse.string "bench"
                 return (UserConstraintStanzas pkgname [BenchStanzas])))
-        <++ (do skipSpaces1
+        <++ (do Parse.skipSpaces1
                 flags <- parseFlagAssignment
                 return (UserConstraintFlags pkgname flags))
 
@@ -791,7 +791,7 @@ dispFlagAssignment = Disp.hsep . map dispFlagValue
     dispFlagName = Disp.text . unFlagName
 
 parseFlagAssignment :: Parse.ReadP r FlagAssignment
-parseFlagAssignment = Parse.sepBy1 parseFlagValue skipSpaces1
+parseFlagAssignment = Parse.sepBy1 parseFlagValue Parse.skipSpaces1
   where
     parseFlagValue =
           (do Parse.optional (Parse.char '+')
@@ -808,7 +808,3 @@ parseFlagAssignment = Parse.sepBy1 parseFlagValue skipSpaces1
         identChar c   = isAlphaNum c || c == '_' || c == '-'
         check ('-':_) = Parse.pfail
         check _       = return ()
-
-skipSpaces1 :: Parse.ReadP r ()
-skipSpaces1 = Parse.satisfy isSpace >> Parse.skipSpaces
-