upload: fix repos with non-null uriPath

This commit fixes the handling of repo URIs that have a non-null uriPath.
Previously, the code would just override the uriPath if the repo had one.
For example, "http://hackage.haskell.org/foo" as repo would lead to the upload URI
"http://hackage.haskell.org/upload".

Even using `parseRelativeReference "upload"` (instead of "/upload") doesn't work, since
that will replace the last path component of the URI path (i.e. "/foo/bar" would generate
the URI "/foo/upload", but we want "/foo/bar/upload").

cabal-install/Distribution/Client/Upload.hs

@@ -15,7 +15,7 @@ import Distribution.Client.Config
 import qualified Distribution.Client.BuildReports.Anonymous as BuildReport
 import qualified Distribution.Client.BuildReports.Upload as BuildReport
 
-import Network.URI (URI(uriPath), parseURI, parseRelativeReference, relativeTo)
+import Network.URI (URI(uriPath), parseURI)
 
 import System.IO        (hFlush, stdin, stdout, hGetEcho, hSetEcho)
 import Control.Exception (bracket)
@@ -26,9 +26,6 @@ import Control.Monad (forM_, when)
 
 type Auth = Maybe (String, String)
 
-uploadReference :: URI
-Just uploadReference = parseRelativeReference "/upload"
-
 checkURI :: URI
 Just checkURI = parseURI "http://hackage.haskell.org/cgi-bin/hackage-scripts/check-pkg"
 
@@ -39,7 +36,10 @@ upload transport verbosity repos mUsername mPassword paths = do
         [] -> die $ "Cannot upload. No remote repositories are configured."
         rs -> remoteRepoTryUpgradeToHttps transport (last rs)
     let targetRepoURI = remoteRepoURI targetRepo
-        uploadURI = uploadReference `relativeTo` targetRepoURI
+        rootIfEmpty x = if null x then "/" else x
+        uploadURI = targetRepoURI {
+            uriPath = rootIfEmpty (uriPath targetRepoURI) FilePath.Posix.</> "upload"
+        }
     Username username <- maybe promptUsername return mUsername
     Password password <- maybe promptPassword return mPassword
     let auth = Just (username,password)