Load plugins when compiling each module (#983)

* WIP: Load (typechecker) plugins from language pragmas

* Revert "Load plugins when starting a GHC session (#905)"

This reverts commit 72d82e5.

* Simplify plugin initialization code

Author: harpocrates

haddock-api/src/Haddock.hs

@@ -76,7 +76,6 @@ import Packages
 import Panic (handleGhcException)
 import Module
 import FastString
-import qualified DynamicLoading
 
 --------------------------------------------------------------------------------
 -- * Exception handling
@@ -450,10 +449,7 @@ withGhc' libDir flags ghcActs = runGhc (Just libDir) $ do
   -- that may need to be re-linked: Haddock doesn't do any
   -- dynamic or static linking at all!
   _ <- setSessionDynFlags dynflags''
-  hscenv <- GHC.getSession
-  dynflags''' <- liftIO (DynamicLoading.initializePlugins hscenv dynflags'')
-  _ <- setSessionDynFlags dynflags'''
-  ghcActs dynflags'''
+  ghcActs dynflags''
   where
 
     -- ignore sublists of flags that start with "+RTS" and end in "-RTS"

haddock-api/src/Haddock/Interface.hs

@@ -64,6 +64,7 @@ import Name (nameIsFromExternalPackage, nameOccName)
 import OccName (isTcOcc)
 import RdrName (unQualOK, gre_name, globalRdrEnvElts)
 import ErrUtils (withTiming)
+import DynamicLoading (initializePlugins)
 
 #if defined(mingw32_HOST_OS)
 import System.IO
@@ -177,7 +178,13 @@ createIfaces verbosity flags instIfaceMap mods = do
 processModule :: Verbosity -> ModSummary -> [Flag] -> IfaceMap -> InstIfaceMap -> Ghc (Maybe (Interface, ModuleSet))
 processModule verbosity modsum flags modMap instIfaceMap = do
   out verbosity verbose $ "Checking module " ++ moduleString (ms_mod modsum) ++ "..."
-  tm <- {-# SCC "parse/typecheck/load" #-} loadModule =<< typecheckModule =<< parseModule modsum
+
+  -- Since GHC 8.6, plugins are initialized on a per module basis
+  hsc_env' <- getSession
+  dynflags' <- liftIO (initializePlugins hsc_env' (GHC.ms_hspp_opts modsum))
+  let modsum' = modsum { ms_hspp_opts = dynflags' }
+
+  tm <- {-# SCC "parse/typecheck/load" #-} loadModule =<< typecheckModule =<< parseModule modsum'
 
   if not $ isBootSummary modsum then do
     out verbosity verbose "Creating interface..."