build: require GHC 7.6 for bootstrapping

Summary:
Per the usual standards, a build of GHC is only compileable
by the last two releases (e.g. 7.8 only by 7.4 and 7.6). To make sure
we don't get suckered into supporting older compilers, let's remove
this support now.

Signed-off-by: Austin Seipp <austin@well-typed.com>

Test Plan:
Try to bootstrap with GHC 7.4, watch it fail. Bootstrap
with 7.6 or better, and everything works.

Reviewers: hvr

Reviewed By: hvr

Subscribers: simonmar, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D167

4 files changed, 1 insertions, 39 deletions

diff --git a/compiler/cmm/SMRep.lhs b/compiler/cmm/SMRep.lhs
index 0713620c5a..53c9d0a5e8 100644
--- a/compiler/cmm/SMRep.lhs
+++ b/compiler/cmm/SMRep.lhs
@@ -105,11 +105,7 @@ StgWord is a type representing an StgWord on the target platform.
 \begin{code}
 -- A Word64 is large enough to hold a Word for either a 32bit or 64bit platform
 newtype StgWord = StgWord Word64
-    deriving (Eq,
-#if __GLASGOW_HASKELL__ < 706
-              Num,
-#endif
-              Bits)
+    deriving (Eq, Bits)
 
 fromStgWord :: StgWord -> Integer
 fromStgWord (StgWord i) = toInteger i
diff --git a/compiler/ghci/Linker.lhs b/compiler/ghci/Linker.lhs
index 40b83bbbae..86d7b268d0 100644
--- a/compiler/ghci/Linker.lhs
+++ b/compiler/ghci/Linker.lhs
@@ -63,11 +63,7 @@ import Control.Concurrent.MVar
 
 import System.FilePath
 import System.IO
-#if __GLASGOW_HASKELL__ > 704
 import System.Directory hiding (findFile)
-#else
-import System.Directory
-#endif
 
 import Distribution.Package hiding (depends, mkPackageKey, PackageKey)
 
diff --git a/compiler/utils/Panic.lhs b/compiler/utils/Panic.lhs
index 583174b201..23bf01cafe 100644
--- a/compiler/utils/Panic.lhs
+++ b/compiler/utils/Panic.lhs
@@ -35,9 +35,6 @@ import Exception
 
 import Control.Concurrent
 import Data.Dynamic
-#if __GLASGOW_HASKELL__ < 705
-import Data.Maybe
-#endif
 import Debug.Trace        ( trace )
 import System.IO.Unsafe
 import System.Exit
@@ -52,10 +49,7 @@ import GHC.ConsoleHandler
 #endif
 
 import GHC.Stack
-
-#if __GLASGOW_HASKELL__ >= 705
 import System.Mem.Weak  ( Weak, deRefWeak )
-#endif
 
 -- | GHC's own exception type
 --   error messages all take the form:
@@ -286,7 +280,6 @@ installSignalHandlers = do
   return ()
 #endif
 
-#if __GLASGOW_HASKELL__ >= 705
 {-# NOINLINE interruptTargetThread #-}
 interruptTargetThread :: MVar [Weak ThreadId]
 interruptTargetThread = unsafePerformIO (newMVar [])
@@ -306,19 +299,6 @@ peekInterruptTargetThread =
      case r of
        Nothing -> loop ts
        Just t  -> return (Just t)
-#else
-{-# NOINLINE interruptTargetThread #-}
-interruptTargetThread :: MVar [ThreadId]
-interruptTargetThread = unsafePerformIO (newMVar [])
-
-pushInterruptTargetThread :: ThreadId -> IO ()
-pushInterruptTargetThread tid = do
- modifyMVar_ interruptTargetThread $ return . (tid :)
-
-peekInterruptTargetThread :: IO (Maybe ThreadId)
-peekInterruptTargetThread =
-  withMVar interruptTargetThread $ return . listToMaybe
-#endif
 
 popInterruptTargetThread :: IO ()
 popInterruptTargetThread =
diff --git a/compiler/utils/Util.lhs b/compiler/utils/Util.lhs
index 2dcc73fd89..dfac0ae020 100644
--- a/compiler/utils/Util.lhs
+++ b/compiler/utils/Util.lhs
@@ -129,10 +129,6 @@ import qualified Data.IntMap as IM
 import qualified Data.Set as Set
 
 import Data.Time
-#if __GLASGOW_HASKELL__ < 705
-import Data.Time.Clock.POSIX
-import System.Time
-#endif
 
 infixr 9 `thenCmp`
 \end{code}
@@ -954,13 +950,7 @@ doesDirNameExist fpath = case takeDirectory fpath of
 -- Backwards compatibility definition of getModificationTime
 
 getModificationUTCTime :: FilePath -> IO UTCTime
-#if __GLASGOW_HASKELL__ < 705
-getModificationUTCTime f = do
-    TOD secs _ <- getModificationTime f
-    return $ posixSecondsToUTCTime (realToFrac secs)
-#else
 getModificationUTCTime = getModificationTime
-#endif
 
 -- --------------------------------------------------------------
 -- check existence & modification time at the same time