ghc, ghc-pkg: use getExecutablePath on Windows when base >= 4.11.0

Summary:
This completes the work started in D4227 by using just 'getExecutablePath'
in ghc and ghc-pkg when building with base >= 4.11.0.

On the long term, we will be able to simply kill the existing code that
follows (or not) symlinks and just get this behaviour for free from
getExecutable. For now we however have to require base >= 4.11.0 to be able
to just use getExecutablePath under Windows, and use the current code when
building with an older base.

Original code by @alpmestan commandeering since patch has been stale
and bug remains open.

Test Plan: Validate

Reviewers: angerman, bgamari, erikd, alpmestan

Reviewed By: bgamari

Subscribers: carter, rwbarton, thomie

GHC Trac Issues: #14483

Differential Revision: https://phabricator.haskell.org/D4229

1 files changed, 25 insertions, 13 deletions

diff --git a/utils/ghc-pkg/Main.hs b/utils/ghc-pkg/Main.hs
index 69137eb4e4..3aa4186db4 100644
--- a/utils/ghc-pkg/Main.hs
+++ b/utils/ghc-pkg/Main.hs
@@ -17,6 +17,24 @@
 #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.
@@ -66,7 +84,7 @@ 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)
+#if defined(darwin_HOST_OS) || defined(linux_HOST_OS) || SIMPLE_WIN_GETLIBDIR
 import System.Environment ( getExecutablePath )
 #endif
 import System.IO
@@ -80,10 +98,12 @@ import qualified Data.Set as Set
 import qualified Data.Map as Map
 
 #if defined(mingw32_HOST_OS)
--- mingw32 needs these for getExecDir
+#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)
@@ -2194,7 +2214,8 @@ dieForcible s = die (s ++ " (use --force to override)")
 -- Cut and pasted from ghc/compiler/main/SysTools
 
 getLibDir :: IO (Maybe String)
-#if defined(mingw32_HOST_OS)
+
+#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
 
@@ -2233,16 +2254,7 @@ getExecPath = try_size 2048 -- plenty, PATH_MAX is 512 under Win32.
 
 foreign import WINDOWS_CCONV unsafe "windows.h GetModuleFileNameW"
   c_GetModuleFileName :: Ptr () -> CWString -> Word32 -> IO Word32
-#elif defined(darwin_HOST_OS) || defined(linux_HOST_OS)
--- TODO: a) this is copy-pasta from SysTools.hs / getBaseDir. Why can't we reuse
---          this here? and parameterise getBaseDir over the executable (for
---          windows)?
---          Answer: we can not, because if we share `getBaseDir` via `ghc-boot`,
---                  that would add `base` as a dependency for windows.
---       b) why is the windows getBaseDir logic, not part of getExecutablePath?
---          it would be much wider available then and we could drop all the
---          custom logic?
---          Answer: yes this should happen. No one has found the time just yet.
+#elif SIMPLE_WIN_GETLIBDIR || defined(darwin_HOST_OS) || defined(linux_HOST_OS)
 getLibDir = Just . (\p -> p </> "lib") . takeDirectory . takeDirectory <$> getExecutablePath
 #else
 getLibDir = return Nothing