Add custom Setup.hs code to warn users about unsupported environments

Setup.hs

@@ -1,2 +1,64 @@
 import Distribution.Simple
-main = defaultMain
+import Distribution.Simple.LocalBuildInfo
+
+import Control.Monad
+import Control.Applicative
+import Data.Version
+import System.Process
+import System.Exit
+import Text.ParserCombinators.ReadP
+
+-- import Data.Monoid
+-- import Distribution.Simple.Setup
+-- import Distribution.Simple.InstallDirs
+-- main = defaultMainWithHooks $ simpleUserHooks {
+--     confHook = \desc cf -> do
+--         print desc
+--         print cf
+--         (confHook simpleUserHooks) desc cf {
+--             configProgSuffix =
+--                 configProgSuffix cf `mappend` toFlag (toPathTemplate "$compiler")
+--         }
+--  }
+
+main :: IO ()
+main = defaultMainWithHooks $ simpleUserHooks {
+    postConf = \args cf desc lbi -> do
+        -- I hope they never change this ;)
+        ["cabal-install", "version", _cabalInstallVer, "using", "version", cabalVer', "of", "the", "Cabal", "library"] <- words <$> readProcess "cabal" ["--version"] ""
+
+        let
+          ghcVer = compilerVersion (compiler lbi)
+          cabalVer = parseVer cabalVer'
+
+          -- ghc >= 7.10?
+          minGhc710 = ghcVer `withinRange` orLaterVersion (parseVer "7.10")
+
+          [libCabalVer] = [ ver | (_, PackageIdentifier pkg ver)
+                                    <- externalPackageDeps lbi
+                          , pkg == PackageName "Cabal" ]
+
+        if minGhc710 then
+            -- make sure Cabal versions are consistent
+            when (not $ cabalVer `sameMajorVersionAs` libCabalVer) $ do
+                 putStrLn $ "Error: Cabal seems to have decided ghc-mod should be built using Cabal version "++showVersion libCabalVer++ " while the `cabal' executable in your PATH was built with Cabal version "++showVersion cabalVer++ ". This will lead to conflicts when running ghc-mod in any project where you use this `cabal' executable. Please compile ghc-mod using the same Cabal version as your `cabal' executable or recompile cabal-install using this version of the Cabal library. (See https://github.com/kazu-yamamoto/ghc-mod/wiki/InconsistentCabalVersions )"
+                 exitFailure
+
+        else -- ghc < 7.10
+            -- make sure Cabal version is < 1.22
+            when (not $ cabalVer `earlierVersionThan` (parseVer "1.22")) $ do
+                 putStrLn "Error: when ghc-mod is built with GHC version < 7.10 only Cabal < 1.22 is supported. (See https://github.com/kazu-yamamoto/ghc-mod/wiki/InconsistentCabalVersions )"
+                 exitFailure
+
+        (postConf simpleUserHooks) args cf desc lbi
+   }
+ where
+   parseVer str =
+       case filter ((=="") . snd) $ readP_to_S parseVersion str of
+         [(ver, _)] -> ver
+         _ -> error $ "No parse (Ver) :(\n" ++ str ++ "\n"
+
+   earlierVersionThan ver ver' =
+       ver `withinRange` earlierVersion ver'
+   sameMajorVersionAs ver ver' =
+       ver `withinRange` withinVersion (Version (take 2 $ versionBranch ver') [])