Docs

Author: wz1000

Diff for: ghcide/src/Development/IDE/Core/Compile.hs

@@ -158,9 +158,9 @@ computePackageDeps env pkg = do
             T.pack $ "unknown package: " ++ show pkg]
         Just pkgInfo -> return $ Right $ unitDepends pkgInfo
 
-data TypecheckHelpers
+newtype TypecheckHelpers
   = TypecheckHelpers
-  { getLinkables       :: !([NormalizedFilePath] -> IO [LinkableResult])
+  { getLinkables       :: !([NormalizedFilePath] -> IO [LinkableResult]) -- ^ hls-graph action to get linkables for files
   }
 
 typecheckModule :: IdeDefer

Diff for: ghcide/src/Development/IDE/Core/Rules.hs

@@ -1104,11 +1104,21 @@ getLinkableRule recorder =
               Just obj_t
                 | obj_t >= core_t -> pure ([], Just $ HomeModInfo hirModIface hirModDetails (Just $ LM (posixSecondsToUTCTime obj_t) (ms_mod ms) [DotO obj_file]))
               _ -> liftIO $ coreFileToLinkable linkableType (hscEnv session) ms hirModIface hirModDetails bin_core (error "object doesn't have time")
-        -- Record the linkable so we know not to unload it
+        -- Record the linkable so we know not to unload it, and unload old versions
         whenJust (hm_linkable =<< hmi) $ \(LM time mod _) -> do
             compiledLinkables <- getCompiledLinkables <$> getIdeGlobalAction
             liftIO $ modifyVar compiledLinkables $ \old -> do
               let !to_keep = extendModuleEnv old mod time
+              --We need to unload old linkables before we can load in new linkables. However,
+              --the unload function in the GHC API takes a list of linkables to keep (i.e.
+              --not unload). Earlier we unloaded right before loading in new linkables, which
+              --is effectively once per splice. This can be slow as unload needs to walk over
+              --the list of all loaded linkables, for each splice.
+              --
+              --Solution: now we unload old linkables right after we generate a new linkable and
+              --just before returning it to be loaded. This has a substantial effect on recompile
+              --times as the number of loaded modules and splices increases.
+              --
               unload (hscEnv session) (map (\(mod, time) -> LM time mod []) $ moduleEnvToList to_keep)
               return (to_keep, ())
         return (hash <$ hmi, (warns, LinkableResult <$> hmi <*> pure hash))