Fix getDefinition in GHC 8.4

Did it break before 0.2.0 or after?

src/Development/IDE/Core/Rules.hs

@@ -675,6 +675,7 @@ getModSummaryRule = defineEarlyCutoff $ \GetModSummary f -> do
 
 getModIfaceRule :: Rules ()
 getModIfaceRule = define $ \GetModIface f -> do
+#if MIN_GHC_API_VERSION(8,6,0) && !defined(GHC_LIB)
     fileOfInterest <- use_ IsFileOfInterest f
     let useHiFile =
           -- Never load interface files for files of interest
@@ -725,6 +726,13 @@ getModIfaceRule = define $ \GetModIface f -> do
       extract (Just tmr) =
         -- Bang patterns are important to force the inner fields
         Just $! HiFileResult (tmrModSummary tmr) (hm_iface $ tmrModInfo tmr)
+#else
+    tm <- use TypeCheck f
+    let modIface = hm_iface . tmrModInfo <$> tm
+        modSummary = tmrModSummary <$> tm
+    return $ ([], HiFileResult <$> modSummary <*> modIface)
+#endif
+
 
 isFileOfInterestRule :: Rules ()
 isFileOfInterestRule = defineEarlyCutoff $ \IsFileOfInterest f -> do

src/Development/IDE/GHC/Compat.hs

@@ -94,6 +94,7 @@ import TcRnTypes
 import System.IO
 import Foreign.ForeignPtr
 import MkIface
+import System.IO.Error
 
 
 hPutStringBuffer :: Handle -> StringBuffer -> IO ()
@@ -263,7 +264,7 @@ supportsHieFiles = False
 
 writeHieFile _ _ = return ()
 
-readHieFile _ _ = return undefined
+readHieFile _ fp = ioError $ mkIOError doesNotExistErrorType "" Nothing (Just fp)
 
 #endif