[GHC] #15481: TH fails to recover from reifyFixity with -fexternal-interpreter

6 Aug 2018

      #15481: TH fails to recover from reifyFixity with -fexternal-interpreter
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.8.1
          Component:  Template       |           Version:  8.4.3
  Haskell                            |
           Keywords:  RemoteGHCi     |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 (Originally reported at https://github.com/glguy/th-
 abstraction/issues/53.)

 If you compile the following program:

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

 import Language.Haskell.TH

 main :: IO ()
 main = putStrLn $(recover (stringE "reifyFixity failed")
                           (do foo <- newName "foo"
                               _ <- reifyFixity foo
                               stringE "reifyFixity successful"))
 }}}

 It will work fine without the use of `-fexternal-interpreter`. However,
 using `-fexternal-interpreter` will result in an error:

 {{{
 $ /opt/ghc/8.4.3/bin/ghc Bug.hs -fforce-recomp
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 $ /opt/ghc/8.4.3/bin/ghc Bug.hs -fforce-recomp -fexternal-interpreter
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

 Bug.hs:7:19: error:
     • The exact Name ‘foo_a3MT’ 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:
         $(recover
             (stringE "reifyFixity failed")
             (do foo <- newName "foo"
                 _ <- reifyFixity foo
                 stringE "reifyFixity successful"))
   |
 7 | main = putStrLn $(recover (stringE "reifyFixity failed")
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...

 Bug.hs:7:19: error:
     • The exact Name ‘foo_a3MT’ 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:
         $(recover
             (stringE "reifyFixity failed")
             (do foo <- newName "foo"
                 _ <- reifyFixity foo
                 stringE "reifyFixity successful"))
   |
 7 | main = putStrLn $(recover (stringE "reifyFixity failed")
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15481
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