[GHC] #16404: Type error recovery crash

7 Mar 2019


      #16404: Type error recovery crash
-------------------------------------+-------------------------------------
           Reporter:  simonpj        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.6.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 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 }
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16404
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler