#16404: Type error recovery crash -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: | -------------------------------------+------------------------------------- Old description:

This program is derived from #16376: {{{ {-# LANGUAGE TypeApplications #-} module Bug where

h x = let f = id @Maybe in Just f }}} If you compile with `-fdefer-type-errors -dcore-lint` you'll get {{{ *** Core Lint errors : in result of Desugar (before optimization) *** <no location info>: warning: In the expression: f_arZ @ a_at1 Out of scope: f_arZ :: forall a. a [LclId] *** Offending Program *** Rec { $trModule :: Module [LclIdX] $trModule = Module (TrNameS "main"#) (TrNameS "T16376"#)

h :: forall p a. p -> Maybe a [LclIdX] h = \ (@ p_asV) (@ a_at1) -> case typeError @ ('TupleRep '[]) @ ((* -> *) ~# *) "T16376.hs:4:19: error:\n\ \ \\226\\128\\162 Expecting one more argument to \\226\\128\\152Maybe\\226\\128\\153\n\ \ Expected a type, but \\226\\128\\152Maybe\\226\\128\\153 has kind \\226\\128\\152* -> *\\226\\128\\153\n\ \ \\226\\128\\162 In the type \\226\\128\\152Maybe\\226\\128\\153\n\ \ In the expression: id @Maybe\n\ \ In an equation for \\226\\128\\152f\\226\\128\\153: f = id @Maybe\n\ \(deferred type error)"# of co_asZ { __DEFAULT -> letrec { h_at5 :: p_asV -> Maybe a_at1 [LclId] h_at5 = \ (x_arY :: p_asV) -> Just @ a_at1 (f_arZ @ a_at1); } in h_at5 } end Rec } }}}

New description: This program is derived from #16376: {{{ {-# LANGUAGE TypeApplications #-} module Bug where h x = let f = id @Maybe in Just f }}} If you compile with `-fdefer-type-errors -dcore-lint` you'll get {{{ *** Core Lint errors : in result of Desugar (before optimization) *** <no location info>: warning: In the expression: f_arZ @ a_at1 Out of scope: f_arZ :: forall a. a [LclId] *** Offending Program *** Rec { $trModule :: Module [LclIdX] $trModule = Module (TrNameS "main"#) (TrNameS "T16376"#) h :: forall p a. p -> Maybe a [LclIdX] h = \ (@ p_asV) (@ a_at1) -> case typeError @ ('TupleRep '[]) @ ((* -> *) ~# *) "T16376.hs:4:19: error:\n\ \ \\226\\128\\162 Expecting one more argument to \\226\\128\\152Maybe\\226\\128\\153\n\ \ Expected a type, but \\226\\128\\152Maybe\\226\\128\\153 has kind \\226\\128\\152* -> *\\226\\128\\153\n\ \ \\226\\128\\162 In the type \\226\\128\\152Maybe\\226\\128\\153\n\ \ In the expression: id @Maybe\n\ \ In an equation for \\226\\128\\152f\\226\\128\\153: f = id @Maybe\n\ \(deferred type error)"# of co_asZ { __DEFAULT -> letrec { h_at5 :: p_asV -> Maybe a_at1 [LclId] h_at5 = \ (x_arY :: p_asV) -> Just @ a_at1 (f_arZ @ a_at1); } in h_at5 } end Rec } }}} Without Lint it just squeezes by, because that `case typeError of ..." discards the "..." since it is unreachable -- Comment (by simonpj): The breakage is worse for GHCi, with `-fdefer-type-errors`, because the `case (typeError "...") ...` transformation doesn't happen, so `f` is still there at the end: {{{ ==================== Simplified expression ==================== case Control.Exception.Base.typeError @ ('GHC.Types.TupleRep '[]) @ ((* -> *) GHC.Prim.~# *) "<interactive>:2:9: error:\n\ \ \\226\\128\\162 Expecting one more argument to \\226\\128\\152Maybe\\226\\128\\153\n\ \ Expected a type, but \\226\\128\\152Maybe\\226\\128\\153 has kind \\226\\128\\152* -> *\\226\\128\\153\n\ \ \\226\\128\\162 In the type \\226\\128\\152Maybe\\226\\128\\153\n\ \ In the expression: id @Maybe\n\ \ In an equation for \\226\\128\\152f\\226\\128\\153: f = id @Maybe\n\ \(deferred type error)"# of co_a1zL { __DEFAULT -> GHC.Base.returnIO @ [()] (GHC.Types.: @ () (f_a1yP `cast` (UnsafeCo representational (forall a. a) () :: (forall a. a) ~R# ())) (GHC.Types.[] @ ())) } }}} which leads to an outright crash. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16404#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler