use Cabal to determine program locations

yesod/ghcwrapper.hs

@@ -5,37 +5,55 @@
 {-# LANGUAGE CPP #-}
 module Main where
 
-import System.Process (rawSystem, readProcess)
-import System.Environment (getArgs)
-import Data.Maybe (fromMaybe)
 import Control.Monad (when)
-import System.Exit (exitWith)
+import Data.Maybe (fromMaybe)
+
+import Distribution.Compiler (CompilerFlavor(..))
+import Distribution.Simple.Configure (configCompiler)
+import Distribution.Simple.Program (defaultProgramConfiguration, programPath, ghcProgram,
+                                    ldProgram, arProgram)
+import Distribution.Simple.Program.Db (lookupProgram, configureProgram)
+import Distribution.Simple.Program.Types (Program(..))
+import Distribution.Verbosity (silent)
+
 import System.Directory (doesDirectoryExist)
+import System.Environment (getArgs)
+import System.Exit (exitWith, ExitCode(..))
+import System.IO (hPutStrLn, stderr)
+import System.Process (rawSystem, readProcess)
+
 
 #ifdef LDCMD
-cmd = lookupGhcInfo "ld command" "ld"
+cmd :: Program
+cmd = ldProgram
 outFile = "dist/ldargs.txt"
 #else
 #ifdef ARCMD
-cmd = lookupGhcInfo "ar command" "ar"
+cmd :: Program
+cmd = arProgram
 outFile ="dist/arargs.txt"
 #else
-cmd = return "ghc"
+cmd :: Program
+cmd = ghcProgram
 outFile = "dist/ghcargs.txt"
 #endif
 #endif
 
-lookupGhcInfo :: String -> String -> IO String
-lookupGhcInfo xs d = fmap (fromMaybe d . lookup xs . read) (readProcess "ghc" ["--info"] "")
-
-passthrough args = do
-  c <- cmd
-  rawSystem c args
+runProgram :: Program -> [String] -> IO ExitCode
+runProgram pgm args = do
+  (comp, pgmc) <- configCompiler (Just GHC) Nothing Nothing defaultProgramConfiguration silent
+  pgmc' <- configureProgram silent pgm pgmc
+  case lookupProgram pgm pgmc' of
+    Nothing -> do
+      hPutStrLn stderr ("cannot find program '" ++ programName pgm ++ "'")
+      return (ExitFailure 1)
+    Just p -> rawSystem (programPath p) args
 
 main = do
   args <- getArgs
   e <- doesDirectoryExist "dist"
   when e $ writeFile outFile (show args ++ "\n")
-  ex <- passthrough args
+  ex <- runProgram cmd args
   exitWith ex
 
+

yesod/yesod.cabal

@@ -94,18 +94,21 @@ library
 executable             yesod-ghc-wrapper
     main-is: ghcwrapper.hs
     build-depends:
-                   base                       >= 4         && < 5
+                    base                       >= 4         && < 5
+                  , Cabal                      >= 1.10      && < 1.16
 
 executable             yesod-ld-wrapper
     main-is: ghcwrapper.hs
     cpp-options:     -DLDCMD
     build-depends:
-                   base                       >= 4         && < 5
+                    base                       >= 4         && < 5
+                  , Cabal                      >= 1.10      && < 1.16
 executable             yesod-ar-wrapper
     main-is: ghcwrapper.hs
     cpp-options:     -DARCMD
     build-depends:
-                   base                       >= 4         && < 5
+                     base                       >= 4         && < 5
+                   , Cabal                      >= 1.10      && < 1.16
 
 executable             yesod
     if flag(ghc7)