Use object code for Template Haskell, emit desugarer warnings (haskell/ghcide#836)

* Use object code for TH

* Set target location for TargetFiles

* Fix tests

* hlint

* fix build on 8.10

* fix ghc-lib

* address review comments

* hlint

* better error handling if module headers don't parse

* Always desugar, don't call interactive API functions

* deprioritize desugar when not TH, fix iface handling

* write hie file on save

* more tweaks

* fix tests

* disable desugarer warnings

* use ModGuts for exports map

* don't desugar

* use bytecode

* make HiFileStable early-cutoff

* restore object code

* re-enable desugar

* review comments

* Don't use ModIface for DocMap

* fix docs for the current module

* mark test as broken on windows

Author: wz1000

ghcide/session-loader/Development/IDE/Session.hs

@@ -118,9 +118,12 @@ loadSession dir = do
         -- files in the project so that `knownFiles` can learn about them and
         -- we can generate a complete module graph
     let extendKnownTargets newTargets = do
-          knownTargets <- forM newTargets $ \TargetDetails{..} -> do
-            found <- filterM (IO.doesFileExist . fromNormalizedFilePath) targetLocations
-            return (targetTarget, found)
+          knownTargets <- forM newTargets $ \TargetDetails{..} ->
+            case targetTarget of
+              TargetFile f -> pure (targetTarget, [f])
+              TargetModule _ -> do
+                found <- filterM (IO.doesFileExist . fromNormalizedFilePath) targetLocations
+                return (targetTarget, found)
           modifyVar_ knownTargetsVar $ traverseHashed $ \known -> do
             let known' = HM.unionWith (<>) known $ HM.fromList knownTargets
             when (known /= known') $
@@ -501,6 +504,7 @@ setCacheDir logger prefix hscComponents comps dflags = do
     pure $ dflags
           & setHiDir cacheDir
           & setHieDir cacheDir
+          & setODir cacheDir
 
 
 renderCradleError :: NormalizedFilePath -> CradleError -> FileDiagnostic
@@ -641,7 +645,7 @@ setOptions (ComponentOptions theOpts compRoot _) dflags = do
 setLinkerOptions :: DynFlags -> DynFlags
 setLinkerOptions df = df {
     ghcLink   = LinkInMemory
-  , hscTarget = HscNothing
+  , hscTarget = HscAsm
   , ghcMode = CompManager
   }
 
@@ -657,6 +661,11 @@ setHiDir f d =
     -- override user settings to avoid conflicts leading to recompilation
     d { hiDir      = Just f}
 
+setODir :: FilePath -> DynFlags -> DynFlags
+setODir f d =
+    -- override user settings to avoid conflicts leading to recompilation
+    d { objectDir = Just f}
+
 getCacheDir :: String -> [String] -> IO FilePath
 getCacheDir prefix opts = getXdgDirectory XdgCache (cacheDir </> prefix ++ "-" ++ opts_hash)
     where