Add package tarball redirects for current cabal-install versions

They expect /package/foo-1.0.tar.gz
rather than /package/foo-1.0/foo-1.0.tar.gz

Distribution/Server/Features/LegacyRedirects.hs

@@ -72,6 +72,15 @@ serveLegacyGets = msum
  movedPermanently ("/package/" ++ display (packageId :: PackageId)) $
  toResponse ""
  ]
+ , dir "package" $ path $ \fileName -> methodSP GET $
+ case Posix.splitExtension fileName of
+ (fileName', ".gz") -> case Posix.splitExtension fileName' of
+ (packageStr, ".tar") -> case simpleParse packageStr of
+ Just pkgid ->
+ movedPermanently (packageTarball pkgid) $ toResponse ""
+ _ -> mzero
+ _ -> mzero
+ _ -> mzero
  ]
  where
  -- HTTP 301 is suitable for permanently redirecting pages
@@ -127,11 +136,12 @@ serveArchiveTree = msum
  ]
  ]
  where
- packageTarball :: PackageId -> String
- packageTarball pkgid = "/package/" ++ display pkgid ++ "/" ++ display pkgid ++ ".tar.gz"
-
  docPath pkgid file = "/package/" ++ display pkgid ++ "/" ++ "doc/" ++ file
 
  cabalPath pkgid = "/package/" ++ display pkgid ++ "/"
  ++ display (packageName pkgid) ++ ".cabal"
 
+packageTarball :: PackageId -> String
+packageTarball pkgid = "/package/" ++ display pkgid
+ ++ "/" ++ display pkgid ++ ".tar.gz"
+