[GHC] #13837: Calling qReifyInstances on out-of-scope Name leads to GHC internal error

[GHC]

#13837: Calling qReifyInstances on out-of-scope Name leads to GHC internal error
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Template       |           Version:  8.0.1
  Haskell                            |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 module Bug where

 import Language.Haskell.TH.Lib
 import Language.Haskell.TH.Syntax

 test_local_tyfam_expansion :: String
 test_local_tyfam_expansion =
   $(do fam_name <- newName "Fam"
        stringE . show =<< qReifyInstances fam_name [])
 }}}

 {{{
 $ /opt/ghc/8.2.1/bin/ghci Bug2.hs
 GHCi, version 8.2.0.20170523: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug2.hs, interpreted )

 Bug2.hs:9:5: error:
     • The exact Name ‘Fam_a4pX’ is not in scope
         Probable cause: you used a unique Template Haskell name (NameU),
         perhaps via newName, but did not bind it
         If that's it, then -ddump-splices might be useful
     • In the argument of reifyInstances: Fam_0
       In the untyped splice:
         $(do fam_name <- newName "Fam"
              stringE . show =<< qReifyInstances fam_name [])
   |
 9 |   $(do fam_name <- newName "Fam"
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^...

 Bug2.hs:9:5: error:
     • GHC internal error: ‘Fam_a4pX’ is not in scope during type checking,
 but it passed the renamer
       tcl_env of environment: []
     • In the type ‘Fam_a4pX’
       In the argument of reifyInstances: Fam_0
       In the untyped splice:
         $(do fam_name <- newName "Fam"
              stringE . show =<< qReifyInstances fam_name [])
   |
 9 |   $(do fam_name <- newName "Fam"
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
 }}}

 This appears to have started happening in GHC 7.10, since with 7.8, you
 only get this:

 {{{
 GHCi, version 7.8.4: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 [1 of 1] Compiling Bug              ( Bug2.hs, interpreted )
 Loading package array-0.5.0.0 ... linking ... done.
 Loading package deepseq-1.3.0.2 ... linking ... done.
 Loading package containers-0.5.5.1 ... linking ... done.
 Loading package pretty-1.1.1.1 ... linking ... done.
 Loading package template-haskell ... linking ... done.

 Bug2.hs:9:5:
     The exact Name ‘Fam_a2gK’ is not in scope
       Probable cause: you used a unique Template Haskell name (NameU),
       perhaps via newName, but did not bind it
       If that's it, then -ddump-splices might be useful
     In the argument of reifyInstances: Fam_0
     In the splice:
       $(do { fam_name <- newName "Fam";
              stringE . show =<< qReifyInstances fam_name [] })
 }}}

 This problem appears to be somewhat specific to `qReifyInstances`, since
 switching it out with `qReify` does not trigger the internal error:

 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 module Bug where

 import Language.Haskell.TH.Lib
 import Language.Haskell.TH.Syntax

 test_local_tyfam_expansion :: String
 test_local_tyfam_expansion =
   $(do fam_name <- newName "Fam"
        stringE . show =<< qReify fam_name)
 }}}
 {{{
 GHCi, version 8.2.0.20170523: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug2.hs, interpreted )

 Bug2.hs:9:5: error:
     • The exact Name ‘Fam_a4od’ is not in scope
         Probable cause: you used a unique Template Haskell name (NameU),
         perhaps via newName, but did not bind it
         If that's it, then -ddump-splices might be useful
     • In the untyped splice:
         $(do fam_name <- newName "Fam"
              stringE . show =<< qReify fam_name)
   |
 9 |   $(do fam_name <- newName "Fam"
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^...

 Bug2.hs:9:5: error:
     • The exact Name ‘Fam_a4od’ is not in scope
         Probable cause: you used a unique Template Haskell name (NameU),
         perhaps via newName, but did not bind it
         If that's it, then -ddump-splices might be useful
     • In the untyped splice:
         $(do fam_name <- newName "Fam"
              stringE . show =<< qReify fam_name)
   |
 9 |   $(do fam_name <- newName "Fam"
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^...

 Bug2.hs:9:5: error:
     • ‘Fam_a4od’ is not in the type environment at a reify
     • In the untyped splice:
         $(do fam_name <- newName "Fam"
              stringE . show =<< qReify fam_name)
   |
 9 |   $(do fam_name <- newName "Fam"
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13837>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler