mkTopLevEnv: not interpreted main:Main

[Chris Smith]

Here's a version with fewer flags/features, that acts the same.

I tried removing the loading of an external module, and that did *not*
exhibit the problem.  It also does *not* fail when the file name is
different each time, so the fact that it's the same file, A.hs, each
time is somehow part of the issue.

I'm getting to the point where I can't imagine what this could possibly
be about.


{-# LANGUAGE MagicHash #-}

import System.IO.Unsafe
import GHC.Exts  (unsafeCoerce#)
import GHC.Paths (libdir)

import qualified GHC      as GHC
import qualified DynFlags as GHC

compile :: IO (Maybe Int)
compile = GHC.runGhc (Just libdir) $ do
    dflags <- GHC.getSessionDynFlags
    let dflags' = dflags { GHC.ghcLink = GHC.LinkInMemory }
    GHC.setSessionDynFlags dflags'
    target <- GHC.guessTarget "A.hs" Nothing
    GHC.setTargets [target]
    r <- fmap GHC.succeeded (GHC.load GHC.LoadAllTargets)
    case r of
        True -> do
            mods <- GHC.getModuleGraph
            let mainMod = GHC.ms_mod (head mods)
            GHC.setContext [ mainMod ] [ ]
            v <- GHC.compileExpr "a :: Integer"
            return (Just (unsafeCoerce# v))
        False -> return Nothing

main = do
    writeFile "A.hs" "a = 42"
    print =<< compile