Drop GHC 8.2 compatibility

Summary:
GHC 8.6.1 is out, so now GHC's support window only extends
back to GHC 8.4. This means we can delete gobs of code that were
only used for GHC 8.2 support. Hooray!

Test Plan: ./validate

Reviewers: bgamari, Phyx, erikd

Reviewed By: bgamari, Phyx

Subscribers: rwbarton, erikd, carter

Differential Revision: https://phabricator.haskell.org/D5192

8 files changed, 4 insertions, 185 deletions

diff --git a/compiler/iface/MkIface.hs b/compiler/iface/MkIface.hs
index 4d2fa83f86..e3d1b824be 100644
--- a/compiler/iface/MkIface.hs
+++ b/compiler/iface/MkIface.hs
@@ -1112,9 +1112,6 @@ instance Semigroup RecompileRequired where
 
 instance Monoid RecompileRequired where
   mempty = UpToDate
-#if __GLASGOW_HASKELL__ < 804
-  mappend = (Data.Semigroup.<>)
-#endif
 
 recompileRequired :: RecompileRequired -> Bool
 recompileRequired UpToDate = False
diff --git a/compiler/main/Plugins.hs b/compiler/main/Plugins.hs
index e83ec08805..01a9841119 100644
--- a/compiler/main/Plugins.hs
+++ b/compiler/main/Plugins.hs
@@ -123,9 +123,6 @@ instance Semigroup PluginRecompile where
 
 instance Monoid PluginRecompile where
   mempty = NoForceRecompile
-#if __GLASGOW_HASKELL__ < 804
-  mappend = (Data.Semigroup.<>)
-#endif
 
 type CorePlugin = [CommandLineOption] -> [CoreToDo] -> CoreM [CoreToDo]
 type TcPlugin = [CommandLineOption] -> Maybe TcRnTypes.TcPlugin
diff --git a/compiler/main/SysTools/BaseDir.hs b/compiler/main/SysTools/BaseDir.hs
index f858c8ffad..16f5a44655 100644
--- a/compiler/main/SysTools/BaseDir.hs
+++ b/compiler/main/SysTools/BaseDir.hs
@@ -33,27 +33,8 @@ import System.Environment (getExecutablePath)
 
 -- Windows
 #if defined(mingw32_HOST_OS)
-#  if MIN_VERSION_Win32(2,5,0)
-#    if !MIN_VERSION_base(4,11,0)
-import qualified System.Win32.Types as Win32
-#    endif
-#  else
-import qualified System.Win32.Info as Win32
-#  endif
-#  if MIN_VERSION_base(4,11,0)
 import System.Environment (getExecutablePath)
 import System.Directory (doesDirectoryExist)
-#  else
-import Data.Char
-import Exception
-import Foreign
-import Foreign.C.String
-import System.Directory
-import System.Win32.Types (DWORD, LPTSTR, HANDLE)
-import System.Win32.Types (failIfNull, failIf, iNVALID_HANDLE_VALUE)
-import System.Win32.File (createFile,closeHandle, gENERIC_READ, fILE_SHARE_READ, oPEN_EXISTING, fILE_ATTRIBUTE_NORMAL, fILE_FLAG_BACKUP_SEMANTICS )
-import System.Win32.DLL (loadLibrary, getProcAddress)
-#  endif
 #endif
 
 #if defined(mingw32_HOST_OS)
@@ -154,85 +135,7 @@ getBaseDir :: IO (Maybe String)
 rootDir :: FilePath -> FilePath
 rootDir = takeDirectory . takeDirectory . normalise
 
-#if MIN_VERSION_base(4,11,0)
 getBaseDir = Just . (\p -> p </> "lib") . rootDir <$> getExecutablePath
-#else
--- Assuming we are running ghc, accessed by path  $(stuff)/<foo>/ghc.exe,
--- return the path $(stuff)/lib.
-getBaseDir = try_size 2048 -- plenty, PATH_MAX is 512 under Win32.
-  where
-    try_size size = allocaArray (fromIntegral size) $ \buf -> do
-        ret <- c_GetModuleFileName nullPtr buf size
-        case ret of
-          0 -> return Nothing
-          _ | ret < size -> do
-                path <- peekCWString buf
-                real <- getFinalPath path -- try to resolve symlinks paths
-                let libdir = (buildLibDir . sanitize . maybe path id) real
-                exists <- doesDirectoryExist libdir
-                if exists
-                   then return $ Just libdir
-                   else fail path
-            | otherwise  -> try_size (size * 2)
-
-    -- getFinalPath returns paths in full raw form.
-    -- Unfortunately GHC isn't set up to handle these
-    -- So if the call succeeded, we need to drop the
-    -- \\?\ prefix.
-    sanitize s = if "\\\\?\\" `isPrefixOf` s
-                    then drop 4 s
-                    else s
-
-    buildLibDir :: FilePath -> FilePath
-    buildLibDir s =
-      (takeDirectory . takeDirectory . normalise $ s) </> "lib"
-
-    fail s = panic ("can't decompose ghc.exe path: " ++ show s)
-
-foreign import WINDOWS_CCONV unsafe "windows.h GetModuleFileNameW"
-  c_GetModuleFileName :: Ptr () -> CWString -> Word32 -> IO Word32
-
--- Attempt to resolve symlinks in order to find the actual location GHC
--- is located at. See Trac #11759.
-getFinalPath :: FilePath -> IO (Maybe FilePath)
-getFinalPath name = do
-    dllHwnd <- failIfNull "LoadLibrary"     $ loadLibrary "kernel32.dll"
-    -- Note: The API GetFinalPathNameByHandleW is only available starting from Windows Vista.
-    -- This means that we can't bind directly to it since it may be missing.
-    -- Instead try to find it's address at runtime and if we don't succeed consider the
-    -- function failed.
-    addr_m  <- (fmap Just $ failIfNull "getProcAddress" $ getProcAddress dllHwnd "GetFinalPathNameByHandleW")
-                  `catch` (\(_ :: SomeException) -> return Nothing)
-    case addr_m of
-      Nothing   -> return Nothing
-      Just addr -> do handle  <- failIf (==iNVALID_HANDLE_VALUE) "CreateFile"
-                                        $ createFile name
-                                                     gENERIC_READ
-                                                     fILE_SHARE_READ
-                                                     Nothing
-                                                     oPEN_EXISTING
-                                                     (fILE_ATTRIBUTE_NORMAL .|. fILE_FLAG_BACKUP_SEMANTICS)
-                                                     Nothing
-                      let fnPtr = makeGetFinalPathNameByHandle $ castPtrToFunPtr addr
-                      -- First try to resolve the path to get the actual path
-                      -- of any symlinks or other file system redirections that
-                      -- may be in place. However this function can fail, and in
-                      -- the event it does fail, we need to try using the
-                      -- original path and see if we can decompose that.
-                      -- If the call fails Win32.try will raise an exception
-                      -- that needs to be caught. See #14159
-                      path    <- (Win32.try "GetFinalPathName"
-                                    (\buf len -> fnPtr handle buf len 0) 512
-                                    `finally` closeHandle handle)
-                                `catch`
-                                 (\(_ :: IOException) -> return name)
-                      return $ Just path
-
-type GetFinalPath = HANDLE -> LPTSTR -> DWORD -> DWORD -> IO DWORD
-
-foreign import WINDOWS_CCONV unsafe "dynamic"
-  makeGetFinalPathNameByHandle :: FunPtr GetFinalPath -> GetFinalPath
-#endif
 #elif defined(darwin_HOST_OS) || defined(linux_HOST_OS)
 -- on unix, this is a bit more confusing.
 -- The layout right now is something like
diff --git a/compiler/utils/GhcPrelude.hs b/compiler/utils/GhcPrelude.hs
index 66d01be5f8..3437e65bf4 100644
--- a/compiler/utils/GhcPrelude.hs
+++ b/compiler/utils/GhcPrelude.hs
@@ -12,13 +12,7 @@ module GhcPrelude (module X) where
 -- clashing with the (Outputable.<>) operator which is heavily used
 -- through GHC's code-base.
 
-#if MIN_VERSION_base(4,11,0)
 import Prelude as X hiding ((<>))
-#else
-import Prelude as X
-import Data.Semigroup as X (Semigroup)
-#endif
-
 import Data.Foldable as X (foldl')
 
 {-
diff --git a/configure.ac b/configure.ac
index f7943752cb..0b65770b93 100644
--- a/configure.ac
+++ b/configure.ac
@@ -132,11 +132,6 @@ AC_ARG_VAR(CC_STAGE0, [C compiler command (bootstrap)])
 if test "$WithGhc" != ""; then
   FPTOOLS_GHC_VERSION([GhcVersion], [GhcMajVersion], [GhcMinVersion], [GhcPatchLevel])dnl
 
-  # See #15281
-  if test "$GhcMajVersion" = "8" && test "$GhcMinVersion" = "2" && test "$GhcPatchLevel" = "1"; then
-     AC_MSG_ERROR([GHC 8.2.1 is known to be buggy and cannot bootstrap this GHC release (See Trac 15281); please use GHC 8.2.2 or later.])
-  fi
-
   if test "$GhcMajVersion" = "unknown" || test "$GhcMinVersion" = "unknown"; then
      AC_MSG_ERROR([Cannot determine the version of $WithGhc.  Is it really GHC?])
   fi
@@ -164,8 +159,8 @@ if test "$WithGhc" = ""
 then
     AC_MSG_ERROR([GHC is required.])
 fi
-FP_COMPARE_VERSIONS([$GhcVersion],[-lt],[8.2],
-    [AC_MSG_ERROR([GHC version 8.2 or later is required to compile GHC.])])
+FP_COMPARE_VERSIONS([$GhcVersion],[-lt],[8.4],
+    [AC_MSG_ERROR([GHC version 8.4 or later is required to compile GHC.])])
 
 if test `expr $GhcMinVersion % 2` = "1"
 then
diff --git a/libraries/ghc-boot/GHC/PackageDb.hs b/libraries/ghc-boot/GHC/PackageDb.hs
index 5de3a5fc74..c7984d0edb 100644
--- a/libraries/ghc-boot/GHC/PackageDb.hs
+++ b/libraries/ghc-boot/GHC/PackageDb.hs
@@ -260,9 +260,7 @@ lockPackageDbWith mode file = do
 
 lockPackageDb = lockPackageDbWith ExclusiveLock
 unlockPackageDb (PackageDbLock hnd) = do
-#if MIN_VERSION_base(4,11,0)
     hUnlock hnd
-#endif
     hClose hnd
 
 -- | Mode to open a package db in.
diff --git a/utils/genapply/Main.hs b/utils/genapply/Main.hs
index b30c9f8c46..71b84fde79 100644
--- a/utils/genapply/Main.hs
+++ b/utils/genapply/Main.hs
@@ -19,9 +19,7 @@ module Main(main) where
 -- Needed for TAG_BITS
 #include "../../includes/MachDeps.h"
 
-#if MIN_VERSION_base(4,11,0)
 import Prelude hiding ((<>))
-#endif
 
 import Text.PrettyPrint
 import Data.Word
diff --git a/utils/ghc-pkg/Main.hs b/utils/ghc-pkg/Main.hs
index 3aa4186db4..9cbeb3ac61 100644
--- a/utils/ghc-pkg/Main.hs
+++ b/utils/ghc-pkg/Main.hs
@@ -17,24 +17,6 @@
 #endif
 #endif
 
--- The SIMPLE_WIN_GETLIBDIR macro will only be set when
--- building on windows.
---
--- Its purpose is to let us know whether the Windows implementation of
--- 'getExecutablePath' follows symlinks or not (it does follow them in
--- base >= 4.11). If it does, the implementation of getLibDir is straightforward
--- but if it does not follow symlinks, we need to follow them ourselves here.
--- Once we do not have to support building ghc-pkg with base < 4.11 anymore,
--- we can keep only the simple, straightforward implementation that just uses
--- 'getExecutablePath'.
-#if defined(mingw32_HOST_OS)
-#if MIN_VERSION_base(4,11,0)
-#define SIMPLE_WIN_GETLIBDIR 1
-#else
-#define SIMPLE_WIN_GETLIBDIR 0
-#endif
-#endif
-
 -----------------------------------------------------------------------------
 --
 -- (c) The University of Glasgow 2004-2009.
@@ -84,7 +66,7 @@ import System.Directory ( doesDirectoryExist, getDirectoryContents,
                           getCurrentDirectory )
 import System.Exit ( exitWith, ExitCode(..) )
 import System.Environment ( getArgs, getProgName, getEnv )
-#if defined(darwin_HOST_OS) || defined(linux_HOST_OS) || SIMPLE_WIN_GETLIBDIR
+#if defined(darwin_HOST_OS) || defined(linux_HOST_OS) || defined(mingw32_HOST_OS)
 import System.Environment ( getExecutablePath )
 #endif
 import System.IO
@@ -98,12 +80,6 @@ import qualified Data.Set as Set
 import qualified Data.Map as Map
 
 #if defined(mingw32_HOST_OS)
-#if !SIMPLE_WIN_GETLIBDIR
--- mingw32 needs these for getExecDir when base < 4.11
-import Foreign
-import Foreign.C
-import System.Directory ( canonicalizePath )
-#endif
 import GHC.ConsoleHandler
 #else
 import System.Posix hiding (fdToHandle)
@@ -2215,46 +2191,7 @@ dieForcible s = die (s ++ " (use --force to override)")
 
 getLibDir :: IO (Maybe String)
 
-#if defined(mingw32_HOST_OS) && !SIMPLE_WIN_GETLIBDIR
-subst :: Char -> Char -> String -> String
-subst a b ls = map (\ x -> if x == a then b else x) ls
-
-unDosifyPath :: FilePath -> FilePath
-unDosifyPath xs = subst '\\' '/' xs
-
-getLibDir = do base   <- getExecDir "/ghc-pkg.exe"
-               case base of
-                 Nothing    -> return Nothing
-                 Just base' -> do
-                    libdir <- canonicalizePath $ base' </> "../lib"
-                    exists <- doesDirectoryExist libdir
-                    if exists
-                       then return $ Just libdir
-                       else return Nothing
-
--- (getExecDir cmd) returns the directory in which the current
---                  executable, which should be called 'cmd', is running
--- So if the full path is /a/b/c/d/e, and you pass "d/e" as cmd,
--- you'll get "/a/b/c" back as the result
-getExecDir :: String -> IO (Maybe String)
-getExecDir cmd =
-    getExecPath >>= maybe (return Nothing) removeCmdSuffix
-    where initN n = reverse . drop n . reverse
-          removeCmdSuffix = return . Just . initN (length cmd) . unDosifyPath
-
-getExecPath :: IO (Maybe String)
-getExecPath = try_size 2048 -- plenty, PATH_MAX is 512 under Win32.
-  where
-    try_size size = allocaArray (fromIntegral size) $ \buf -> do
-        ret <- c_GetModuleFileName nullPtr buf size
-        case ret of
-          0 -> return Nothing
-          _ | ret < size -> fmap Just $ peekCWString buf
-            | otherwise  -> try_size (size * 2)
-
-foreign import WINDOWS_CCONV unsafe "windows.h GetModuleFileNameW"
-  c_GetModuleFileName :: Ptr () -> CWString -> Word32 -> IO Word32
-#elif SIMPLE_WIN_GETLIBDIR || defined(darwin_HOST_OS) || defined(linux_HOST_OS)
+#if defined(mingw32_HOST_OS) || defined(darwin_HOST_OS) || defined(linux_HOST_OS)
 getLibDir = Just . (\p -> p </> "lib") . takeDirectory . takeDirectory <$> getExecutablePath
 #else
 getLibDir = return Nothing