Resolve haskell#7065: Encode file+noindex paths as URIs

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

@@ -494,10 +494,6 @@ infixr 4 `archiveTo`
 -- external repository corresponding to all of these packages
 withRepo :: FilePath -> TestM a -> TestM a
 withRepo repo_dir m = do
-    -- https://github.com/haskell/cabal/issues/7065
-    -- you don't simply put a windows path into URL...
-    skipIfWindows
-
     env <- getTestEnv
 
     -- 1. Initialize repo directory
@@ -531,7 +527,14 @@ withRepo repo_dir m = do
     withReaderT (\env' -> env' { testHaveRepo = True }) m
     -- TODO: Arguably should undo everything when we're done...
   where
-    repoUri env ="file+noindex://" ++ testRepoDir env
+    repoUri
+        -- encode path as UNC path on windows.
+        | buildOS == Windows = "file+noindex:///" ++ convertDirSeparators (testRepoDir env)
+        | otherwise env      = "file+noindex://" ++ testRepoDir env
+
+    convertDirSeparators = map $ \c -> case c of
+        '\\' -> '/'
+        c    -> c
 
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