Allow disabling the simplifier in compileModule (#496)

It causes problems for our conversion to DAML-LF atm and isn’t
necessary (since we don’t have template Haskell) so let’s make it
configurable. I originally thought we could just copy paste all of
compileModule to DAML but it turns out that this pull in too much
stuff that I don’t want to see diverge from `ghcide` so I abandoned
that idea.

Author: cocreature

src/Development/IDE/Core/Compile.hs

@@ -9,6 +9,7 @@
 --   Given a list of paths to find libraries, and a file to compile, produce a list of 'CoreModule' values.
 module Development.IDE.Core.Compile
   ( TcModuleResult(..)
+  , RunSimplifier(..)
   , compileModule
   , parseModule
   , typecheckModule
@@ -131,14 +132,21 @@ initPlugins modSummary = do
     return modSummary
 #endif
 
+-- | Whether we should run the -O0 simplifier when generating core.
+--
+-- This is required for template Haskell to work but we disable this in DAML.
+-- See #256
+newtype RunSimplifier = RunSimplifier Bool
+
 -- | Compile a single type-checked module to a 'CoreModule' value, or
 -- provide errors.
 compileModule
-    :: HscEnv
+    :: RunSimplifier
+    -> HscEnv
     -> [TcModuleResult]
     -> TcModuleResult
     -> IO (IdeResult (SafeHaskellMode, CgGuts, ModDetails))
-compileModule packageState deps tmr =
+compileModule (RunSimplifier simplify) packageState deps tmr =
     fmap (either (, Nothing) (second Just)) $
     runGhcEnv packageState $
         catchSrcErrors "compile" $ do
@@ -152,11 +160,12 @@ compileModule packageState deps tmr =
                 let tm' = tm{tm_parsed_module  = pm'}
                 GHC.dm_core_module <$> GHC.desugarModule tm'
             let tc_result = fst (tm_internals_ (tmrModule tmr))
-            -- Have to call the simplifier on the code even if we are at
-            -- -O0 as otherwise the code generation fails which leads to
-            -- errors like #256
-            plugins <- liftIO $ readIORef (tcg_th_coreplugins tc_result)
-            desugared_guts <- liftIO $ hscSimplify session plugins desugar
+            desugared_guts <-
+                if simplify
+                    then do
+                        plugins <- liftIO $ readIORef (tcg_th_coreplugins tc_result)
+                        liftIO $ hscSimplify session plugins desugar
+                    else pure desugar
             -- give variables unique OccNames
             (guts, details) <- liftIO $ tidyProgram session desugared_guts
             return (map snd warnings, (mg_safe_haskell desugar, guts, details))

src/Development/IDE/Core/Rules.hs

@@ -351,17 +351,17 @@ typeCheckRule =
         addByteCode :: Linkable -> TcModuleResult -> TcModuleResult
         addByteCode lm tmr = tmr { tmrModInfo = (tmrModInfo tmr) { hm_linkable = Just lm } }
 
-generateCore :: NormalizedFilePath -> Action (IdeResult (SafeHaskellMode, CgGuts, ModDetails))
-generateCore file = do
+generateCore :: RunSimplifier -> NormalizedFilePath -> Action (IdeResult (SafeHaskellMode, CgGuts, ModDetails))
+generateCore runSimplifier file = do
     deps <- use_ GetDependencies file
     (tm:tms) <- uses_ TypeCheck (file:transitiveModuleDeps deps)
     setPriority priorityGenerateCore
     packageState <- hscEnv <$> use_ GhcSession file
-    liftIO $ compileModule packageState tms tm
+    liftIO $ compileModule runSimplifier packageState tms tm
 
 generateCoreRule :: Rules ()
 generateCoreRule =
-    define $ \GenerateCore -> generateCore
+    define $ \GenerateCore -> generateCore (RunSimplifier True)
 
 generateByteCodeRule :: Rules ()
 generateByteCodeRule =