#13642: GHCi 8.2 simply ignores TH splice using datatype with a forall'd kind signature -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.2.1-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Actually, it extends even beyond GHCi! If you put this into a module: {{{#!hs {-# LANGUAGE GADTs, TypeInType, TemplateHaskell, RankNTypes #-} module Bug where import Data.Kind (Type) import Language.Haskell.TH (stringE, pprint) main :: IO () main = putStrLn $([d| data Foo :: forall a. a -> Type where MkFoo :: Foo Int |] >>= string E . pprint) }}} Then some interesting things happen if you try to compile this. If you try to load it into GHCi, you get this: {{{ $ /opt/ghc/8.2.1/bin/ghci Bug.hs GHCi, version 8.2.0.20170427: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Failed, modules loaded: none. }}} Apparently the module fails to compile, despite the fact that no errors were emitted during compilation. Something similar happens if you directly invoke `ghc` on it: {{{ $ /opt/ghc/8.2.1/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) $ echo $? 1 }}} Again, no errors are emitted, but compilation definitely fails, since no `.hi` or `.o` files are emitted, and you get an error return code of 1. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13642#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13642: GHCi 8.2 simply ignores TH splice using datatype with a forall'd kind signature -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.2.1-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * cc: goldfire (added) Comment: After some digging, the function responsible for suppressing the error message appears to be `dsWhenNoErrs`: {{{#!hs dsWhenNoErrs :: DsM a -> (a -> CoreExpr) -> DsM CoreExpr dsWhenNoErrs thing_inside mk_expr = do { (result, no_errs) <- askNoErrsDs thing_inside ; return $ if no_errs then mk_expr result else unitExpr } }}} For whatever reason, `askNoErrsDs` does not appear to be propagating the error message correctly. There's also similar issues with splicing in any other features which Template Haskell doesn't support. For example, you could just as well use `[d| id x = x {-# SCC id #-} |]` in the example above. goldfire, do you have an idea of what's going on here? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13642#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13642: GHCi 8.2 simply ignores TH splice using datatype with a forall'd kind signature -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.2.1-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"e77019767fe5327011c6dc8fe089c64884120aab/ghc" e770197/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="e77019767fe5327011c6dc8fe089c64884120aab" Deal with exceptions in dsWhenNoErrs Gracious me. Ever since this patch commit 374457809de343f409fbeea0a885877947a133a2 Author: Jan Stolarek Date: Fri Jul 11 13:54:45 2014 +0200 Injective type families TcRnMonad.askNoErrs has been wrong. It looked like this askNoErrs :: TcRn a -> TcRn (a, Bool) askNoErrs m = do { errs_var <- newTcRef emptyMessages ; res <- setErrsVar errs_var m ; (warns, errs) <- readTcRef errs_var ; addMessages (warns, errs) ; return (res, isEmptyBag errs) } The trouble comes if 'm' throws an exception in the TcRn monad. Then 'errs_var is never read, so any errors are simply lost. This mistake was then propgated into DsMonad.dsWhenNoErrs, where it gave rise to Trac #13642. Thank to Ryan for narrowing it down so sharply. I did some refactoring, as usual. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13642#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13642: GHCi 8.2 simply ignores TH splice using datatype with a forall'd kind signature -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.2.1 Component: Template Haskell | Version: 8.2.1-rc1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: th/T13642.hs Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * resolution: => fixed * milestone: => 8.2.1 Comment: Merged with c7642debda55509d805036c28c9804f6c587d44b. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13642#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler