Drop GHC 7.10 compatibility

GHC 8.2.1 is out, so now GHC's support window only extends back to GHC
8.0. This means we can delete gobs of code that was only used for GHC
7.10 support. Hooray!

Test Plan: ./validate

Reviewers: hvr, bgamari, austin, goldfire, simonmar

Reviewed By: bgamari

Subscribers: Phyx, rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3781

7 files changed, 4 insertions, 59 deletions

diff --git a/compiler/utils/IOEnv.hs b/compiler/utils/IOEnv.hs
index 29854c51fe..5a7ccd9972 100644
--- a/compiler/utils/IOEnv.hs
+++ b/compiler/utils/IOEnv.hs
@@ -1,5 +1,3 @@
-{-# LANGUAGE CPP #-}
-
 --
 -- (c) The University of Glasgow 2002-2006
 --
@@ -41,9 +39,7 @@ import Data.IORef       ( IORef, newIORef, readIORef, writeIORef, modifyIORef,
 import System.IO.Unsafe ( unsafeInterleaveIO )
 import System.IO        ( fixIO )
 import Control.Monad
-#if __GLASGOW_HASKELL__ > 710
 import qualified Control.Monad.Fail as MonadFail
-#endif
 import MonadUtils
 import Control.Applicative (Alternative(..))
 
@@ -62,11 +58,8 @@ instance Monad (IOEnv m) where
     (>>)   = (*>)
     fail _ = failM -- Ignore the string
 
-#if __GLASGOW_HASKELL__ > 710
 instance MonadFail.MonadFail (IOEnv m) where
     fail _ = failM -- Ignore the string
-#endif
-
 
 instance Applicative (IOEnv m) where
     pure = returnM
diff --git a/compiler/utils/MonadUtils.hs b/compiler/utils/MonadUtils.hs
index 93a835e04e..d6fb31731e 100644
--- a/compiler/utils/MonadUtils.hs
+++ b/compiler/utils/MonadUtils.hs
@@ -1,5 +1,3 @@
-{-# LANGUAGE CPP #-}
-
 -- | Utilities related to Monad and Applicative classes
 --   Mostly for backwards compatibility.
 
@@ -34,9 +32,6 @@ import Maybes
 import Control.Monad
 import Control.Monad.Fix
 import Control.Monad.IO.Class
-#if __GLASGOW_HASKELL__ < 800
-import Control.Monad.Trans.Error () -- for orphan `instance MonadPlus IO`
-#endif
 
 -------------------------------------------------------------------------------
 -- Lift combinators
diff --git a/compiler/utils/OrdList.hs b/compiler/utils/OrdList.hs
index 3c5b9d7380..1660090ba7 100644
--- a/compiler/utils/OrdList.hs
+++ b/compiler/utils/OrdList.hs
@@ -9,7 +9,6 @@ Provide trees (of instructions), so that lists of instructions
 can be appended in linear time.
 -}
 
-{-# LANGUAGE CPP #-}
 module OrdList (
         OrdList,
         nilOL, isNilOL, unitOL, appOL, consOL, snocOL, concatOL, lastOL,
@@ -18,10 +17,8 @@ module OrdList (
 
 import Outputable
 
-#if __GLASGOW_HASKELL__ > 710
 import Data.Semigroup   ( Semigroup )
 import qualified Data.Semigroup as Semigroup
-#endif
 
 infixl 5  `appOL`
 infixl 5  `snocOL`
@@ -39,10 +36,8 @@ data OrdList a
 instance Outputable a => Outputable (OrdList a) where
   ppr ol = ppr (fromOL ol)  -- Convert to list and print that
 
-#if __GLASGOW_HASKELL__ > 710
 instance Semigroup (OrdList a) where
   (<>) = appOL
-#endif
 
 instance Monoid (OrdList a) where
   mempty = nilOL
diff --git a/compiler/utils/Outputable.hs b/compiler/utils/Outputable.hs
index 4107e5beef..de27546ac4 100644
--- a/compiler/utils/Outputable.hs
+++ b/compiler/utils/Outputable.hs
@@ -122,6 +122,7 @@ import Data.List (intersperse)
 
 import GHC.Fingerprint
 import GHC.Show         ( showMultiLineString )
+import GHC.Stack        ( callStack, prettyCallStack )
 
 {-
 ************************************************************************
@@ -1130,7 +1131,8 @@ doOrDoes _   = text "do"
 
 callStackDoc :: HasCallStack => SDoc
 callStackDoc =
-    hang (text "Call stack:") 4 (vcat $ map text $ lines prettyCurrentCallStack)
+    hang (text "Call stack:")
+       4 (vcat $ map text $ lines (prettyCallStack callStack))
 
 pprPanic :: HasCallStack => String -> SDoc -> a
 -- ^ Throw an exception saying "bug in GHC"
diff --git a/compiler/utils/UniqFM.hs b/compiler/utils/UniqFM.hs
index 71a092b28e..8ea8ba4537 100644
--- a/compiler/utils/UniqFM.hs
+++ b/compiler/utils/UniqFM.hs
@@ -85,10 +85,8 @@ import qualified Data.Monoid as Mon
 import qualified Data.IntSet as S
 import Data.Typeable
 import Data.Data
-#if __GLASGOW_HASKELL__ > 710
 import Data.Semigroup   ( Semigroup )
 import qualified Data.Semigroup as Semigroup
-#endif
 
 
 newtype UniqFM ele = UFM (M.IntMap ele)
@@ -358,10 +356,8 @@ equalKeysUFM (UFM m1) (UFM m2) = M.keys m1 == M.keys m2
 
 -- Instances
 
-#if __GLASGOW_HASKELL__ > 710
 instance Semigroup (UniqFM a) where
   (<>) = plusUFM
-#endif
 
 instance Monoid (UniqFM a) where
     mempty = emptyUFM
diff --git a/compiler/utils/UniqSet.hs b/compiler/utils/UniqSet.hs
index f29a1e6e1f..fcac865ea8 100644
--- a/compiler/utils/UniqSet.hs
+++ b/compiler/utils/UniqSet.hs
@@ -9,7 +9,6 @@ Based on @UniqFMs@ (as you would expect).
 Basically, the things need to be in class @Uniquable@.
 -}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 
 module UniqSet (
@@ -53,9 +52,7 @@ import Data.Coerce
 import Outputable
 import Data.Foldable (foldl')
 import Data.Data
-#if __GLASGOW_HASKELL__ >= 801
 import qualified Data.Semigroup
-#endif
 
 -- Note [UniqSet invariant]
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -189,10 +186,8 @@ unsafeUFMToUniqSet = UniqSet
 
 instance Outputable a => Outputable (UniqSet a) where
     ppr = pprUniqSet ppr
-#if __GLASGOW_HASKELL__ >= 801
 instance Data.Semigroup.Semigroup (UniqSet a) where
   (<>) = mappend
-#endif
 instance Monoid (UniqSet a) where
   mempty = UniqSet mempty
   UniqSet s `mappend` UniqSet t = UniqSet (s `mappend` t)
diff --git a/compiler/utils/Util.hs b/compiler/utils/Util.hs
index 35a6340fd4..6146bf0113 100644
--- a/compiler/utils/Util.hs
+++ b/compiler/utils/Util.hs
@@ -4,11 +4,6 @@
 {-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE BangPatterns #-}
-#if __GLASGOW_HASKELL__ < 800
--- For CallStack business
-{-# LANGUAGE ImplicitParams #-}
-{-# LANGUAGE FlexibleContexts #-}
-#endif
 
 -- | Highly random utility functions
 --
@@ -124,12 +119,8 @@ module Util (
         hashString,
 
         -- * Call stacks
-#if MIN_VERSION_GLASGOW_HASKELL(7,10,2,0)
-        GHC.Stack.CallStack,
-#endif
         HasCallStack,
         HasDebugCallStack,
-        prettyCurrentCallStack,
 
         -- * Utils for flags
         OverridingBool(..),
@@ -147,7 +138,7 @@ import System.IO.Unsafe ( unsafePerformIO )
 import Data.List        hiding (group)
 
 import GHC.Exts
-import qualified GHC.Stack
+import GHC.Stack (HasCallStack)
 
 import Control.Applicative ( liftA2 )
 import Control.Monad    ( liftM )
@@ -1368,16 +1359,6 @@ mulHi a b = fromIntegral (r `shiftR` 32)
    where r :: Int64
          r = fromIntegral a * fromIntegral b
 
--- | A compatibility wrapper for the @GHC.Stack.HasCallStack@ constraint.
-#if __GLASGOW_HASKELL__ >= 800
-type HasCallStack = GHC.Stack.HasCallStack
-#elif MIN_VERSION_GLASGOW_HASKELL(7,10,2,0)
-type HasCallStack = (?callStack :: GHC.Stack.CallStack)
--- CallStack wasn't present in GHC 7.10.1, disable callstacks in stage 1
-#else
-type HasCallStack = (() :: Constraint)
-#endif
-
 -- | A call stack constraint, but only when 'isDebugOn'.
 #if defined(DEBUG)
 type HasDebugCallStack = HasCallStack
@@ -1385,18 +1366,6 @@ type HasDebugCallStack = HasCallStack
 type HasDebugCallStack = (() :: Constraint)
 #endif
 
--- | Pretty-print the current callstack
-#if __GLASGOW_HASKELL__ >= 800
-prettyCurrentCallStack :: HasCallStack => String
-prettyCurrentCallStack = GHC.Stack.prettyCallStack GHC.Stack.callStack
-#elif MIN_VERSION_GLASGOW_HASKELL(7,10,2,0)
-prettyCurrentCallStack :: (?callStack :: GHC.Stack.CallStack) => String
-prettyCurrentCallStack = GHC.Stack.showCallStack ?callStack
-#else
-prettyCurrentCallStack :: HasCallStack => String
-prettyCurrentCallStack = "Call stack unavailable"
-#endif
-
 data OverridingBool
   = Auto
   | Always