Don't modify path separator for URIs

cabal-testsuite/cabal-testsuite.cabal

@@ -72,6 +72,7 @@ library
     , exceptions            ^>= 0.10.0
     , filepath              ^>= 1.3.0.1 || ^>= 1.4.0.0 || ^>= 1.5.0.0
     , Glob                  ^>= 0.10.2
+    , network-uri            >= 2.6.0.2 && < 2.7
     , network-wait          ^>= 0.1.2.0 || ^>= 0.2.0.0
     , optparse-applicative  ^>= 0.14.3.0 || ^>=0.15.1.0 || ^>=0.16.0.0 || ^>= 0.17.0.0 || ^>= 0.18.1.0
     , process               ^>= 1.2.1.0 || ^>= 1.4.2.0 || ^>= 1.6.1.0

cabal-testsuite/src/Test/Cabal/NeedleHaystack.hs

@@ -1,9 +1,13 @@
+{-# LANGUAGE MultiWayIf #-}
+
 module Test.Cabal.NeedleHaystack where
 
+import Data.Maybe (isJust)
 import Distribution.System
 import Data.List (isPrefixOf)
 import qualified System.FilePath.Posix as Posix
 import qualified System.FilePath.Windows as Windows
+import Network.URI (parseURI)
 
 -- | Transformations for the search strings and the text to search in.
 data TxContains =
@@ -58,12 +62,15 @@ lineBreaksToSpaces = unwords . lines . filter ((/=) '\r')
 
 normalizePathSeparator :: FilePath -> FilePath
 normalizePathSeparator p =
-    if buildOS == Windows
-        then
+    if | isURI p -> p
+       | buildOS == Windows ->
             [if Posix.isPathSeparator c then Windows.pathSeparator else c| c <- p]
-        else
+       | otherwise ->
             [if Windows.isPathSeparator c then Posix.pathSeparator else c| c <- p]
 
+isURI :: FilePath -> Bool
+isURI = isJust . parseURI
+
 normalizeWindowsOutput :: String -> String
 normalizeWindowsOutput = unlines . map normalizePathSeparator . lines