Return ModIface in compilation pipeline, remove IORef hack for generating ModIfaces

The compilation phases now optionally return ModIface (for phases that
generate an interface, currently only HscOut when (re)compiling a file).
The value is then used by compileOne' to return the generated interface
with HomeModInfo (which is then used by the batch mode compiler when
building rest of the tree).

hscIncrementalMode also returns a DynFlags with plugin info, to be used
in the rest of the pipeline.

Unfortunately this introduces a (perhaps less bad) hack in place of the
previous IORef: we now record the DynFlags used to generate the partial
infterface in HscRecomp and use the same DynFlags when generating the
full interface. I spent almost three days trying to understand what's
changing in DynFlags that causes a backpack test to fail, but I couldn't
figure it out. There's a FIXME added next to the field so hopefully
someone who understands this better than I do will fix it leter.

1 files changed, 17 insertions, 4 deletions

diff --git a/compiler/main/PipelineMonad.hs b/compiler/main/PipelineMonad.hs
index d152d04530..bdda19ceac 100644
--- a/compiler/main/PipelineMonad.hs
+++ b/compiler/main/PipelineMonad.hs
@@ -7,7 +7,8 @@ module PipelineMonad (
     CompPipeline(..), evalP
   , PhasePlus(..)
   , PipeEnv(..), PipeState(..), PipelineOutput(..)
-  , getPipeEnv, getPipeState, setDynFlags, setModLocation, setForeignOs
+  , getPipeEnv, getPipeState, setDynFlags, setModLocation, setForeignOs, setIface
+  , pipeStateDynFlags, pipeStateModIface
   ) where
 
 import GhcPrelude
@@ -25,8 +26,8 @@ import Control.Monad
 newtype CompPipeline a = P { unP :: PipeEnv -> PipeState -> IO (PipeState, a) }
     deriving (Functor)
 
-evalP :: CompPipeline a -> PipeEnv -> PipeState -> IO a
-evalP f env st = liftM snd $ unP f env st
+evalP :: CompPipeline a -> PipeEnv -> PipeState -> IO (PipeState, a)
+evalP (P f) env st = f env st
 
 instance Applicative CompPipeline where
     pure a = P $ \_env state -> return (state, a)
@@ -67,12 +68,21 @@ data PipeState = PipeState {
        maybe_loc :: Maybe ModLocation,
           -- ^ the ModLocation.  This is discovered during compilation,
           -- in the Hsc phase where we read the module header.
-       foreign_os :: [FilePath]
+       foreign_os :: [FilePath],
          -- ^ additional object files resulting from compiling foreign
          -- code. They come from two sources: foreign stubs, and
          -- add{C,Cxx,Objc,Objcxx}File from template haskell
+       iface :: Maybe ModIface
+         -- ^ Interface generated by HscOut phase. Only available after the
+         -- phase runs.
   }
 
+pipeStateDynFlags :: PipeState -> DynFlags
+pipeStateDynFlags = hsc_dflags . hsc_env
+
+pipeStateModIface :: PipeState -> Maybe ModIface
+pipeStateModIface = iface
+
 data PipelineOutput
   = Temporary TempFileLifetime
         -- ^ Output should be to a temporary file: we're going to
@@ -107,3 +117,6 @@ setModLocation loc = P $ \_env state ->
 setForeignOs :: [FilePath] -> CompPipeline ()
 setForeignOs os = P $ \_env state ->
   return (state{ foreign_os = os }, ())
+
+setIface :: ModIface -> CompPipeline ()
+setIface iface = P $ \_env state -> return (state{ iface = Just iface }, ())