#10078: tcPluginStop of a type checker plugin is not called if an error occurs -------------------------------------+------------------------------------- Reporter: jbracker | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 (Type checker) | Operating System: Linux Keywords: | Type of failure: Incorrect result Architecture: x86_64 | at runtime (amd64) | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- When a module using a type checker plugin produces a compiler error the clean up function `tcPluginStop` of the plugin is not called. I am not sure if this is intended, but according to the description of the wiki page (Plugins/TypeChecker) this should always be called. === Test plugin `MyPlugin.hs`: {{{#!hs module MyPlugin ( plugin ) where import Plugins import TcRnTypes import TcPluginM plugin :: Plugin plugin = defaultPlugin { tcPlugin = \clos -> Just $ TcPlugin { tcPluginInit = tcPluginIO $ putStrLn ">>> Plugin Init" , tcPluginSolve = \_ _ _ _ -> do tcPluginIO $ putStrLn ">>> Plugin Solve" return $ TcPluginOk [] [] , tcPluginStop = \_ -> tcPluginIO $ putStrLn ">>> Plugin Stop" } } }}} === Minimal example (with type error) `Main.hs`: {{{#!hs {-# OPTIONS_GHC -fplugin MyPlugin #-} module Main where main :: (Monad m) => m () main = do return 1 }}} Compiling this will lead to the following output: {{{ $ ~/ghc/inplace/bin/ghc-stage2 --make -package ghc-7.11.20150209 -dynamic Main.hs [2 of 2] Compiling Main ( Main.hs, Main.o )

...

...

Plugin Init Plugin Solve Plugin Solve Plugin Solve

Main.hs:6:10: Could not deduce (Num ()) arising from the literal ‘1’ from the context: Monad m bound by the type signature for: main :: Monad m => m () at Main.hs:4:9-25 In the first argument of ‘return’, namely ‘1’ In a stmt of a 'do' block: return 1 In the expression: do { return 1 } }}} Which means `tcPluginStop` was _not_ called. === Minimal example (without type error) `Main.hs`: {{{#!hs {-# OPTIONS_GHC -fplugin MyPlugin #-} module Main where main :: (Monad m) => m () main = do return () }}} Compiling this will lead to the following output: {{{ $ ~/ghc/inplace/bin/ghc-stage2 --make -package ghc-7.11.20150209 -dynamic Main.hs [2 of 2] Compiling Main ( Main.hs, Main.o ) [MyPlugin changed]

...

...

Plugin Init Plugin Solve Plugin Solve Plugin Stop Linking Main ... }}} Which means `tcPluginStop` _was_ called.

=== Possible solution As far as I can see, the solution to this should be to change the plugin code at the bottom of `typechecker/TcRnDriver.hs` from {{{#!hs withTcPlugins :: HscEnv -> TcM a -> TcM a withTcPlugins hsc_env m = do plugins <- liftIO (loadTcPlugins hsc_env) case plugins of [] -> m -- Common fast case _ -> do (solvers,stops) <- unzip `fmap` mapM startPlugin plugins res <- updGblEnv (\e -> e { tcg_tc_plugins = solvers }) m mapM_ runTcPluginM stops return res where startPlugin (TcPlugin start solve stop) = do s <- runTcPluginM start return (solve s, stop s) }}} to {{{#!hs withTcPlugins :: HscEnv -> TcM a -> TcM a withTcPlugins hsc_env m = do plugins <- liftIO (loadTcPlugins hsc_env) case plugins of [] -> m -- Common fast case _ -> do (solvers,stops) <- unzip `fmap` mapM startPlugin plugins eitherRes <- tryM $ do updGblEnv (\e -> e { tcg_tc_plugins = solvers }) m mapM_ runTcPluginM stops case eitherRes of Left e -> failM Right res -> return res where startPlugin (TcPlugin start solve stop) = do s <- runTcPluginM start return (solve s, stop s) }}} . I have tried this. It compiles and my minimal example delivers the correct result. Are there any arguments against this change? If not, I would try to commit a patch for this problem sometime this weekend. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10078 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler