Support installing multiple ghc-mod instances

core/Language/Haskell/GhcMod/CabalHelper.hs

@@ -16,15 +16,13 @@
 
 {-# LANGUAGE CPP #-}
 module Language.Haskell.GhcMod.CabalHelper
-#ifndef SPEC
   ( getComponents
   , getGhcMergedPkgOptions
   , getCabalPackageDbStack
   , prepareCabalHelper
   , withAutogen
-  )
-#endif
-  where
+  , withCabal
+  ) where
 
 import Control.Applicative
 import Control.Monad

core/Language/Haskell/GhcMod/Cradle.hs

@@ -1,15 +1,14 @@
 {-# LANGUAGE CPP #-}
 module Language.Haskell.GhcMod.Cradle
-#ifndef SPEC
-  (
-    findCradle
+  ( findCradle
   , findCradle'
   , findCradleNoLog
   , findSpecCradle
   , cleanupCradle
-  )
-#endif
-  where
+
+  -- * for @spec@
+  , plainCradle
+  ) where
 
 import Language.Haskell.GhcMod.PathsAndFiles
 import Language.Haskell.GhcMod.Monad.Types

src/GHCModWrapper.hs

@@ -0,0 +1,30 @@
+-- | Dispatcher program to support co-installation of multiple ghc-mod
+-- instances (compiled against different GHC versions) without breaking the
+-- commandline API
+module Main where
+
+import System.IO
+import System.Exit
+import System.Process
+import System.FilePath
+import System.Environment
+import Utils
+
+import Paths_ghc_mod
+
+main :: IO ()
+main = do
+  args <- getArgs
+  libexecdir <- getLibexecDir
+  let installedExe = libexecdir </> "ghc-mod-real"
+  mexe <- mightExist installedExe
+  case mexe of
+    Nothing -> do
+      hPutStrLn stderr $
+        "ghc-mod: Could not find '"++installedExe++"', check your installation!"
+      exitWith $ ExitFailure 1
+
+    Just exe -> do
+      (_, _, _, h) <-
+          createProcess $ proc exe args
+      exitWith =<< waitForProcess h