[GHC] #11680: Out-of-scope suggestion given for an out-of-scope variable when using TH

5 Mar 2016

      #11680: Out-of-scope suggestion given for an out-of-scope variable when using TH
-------------------------------------+-------------------------------------
           Reporter:  jme            |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1-rc2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect
  Unknown/Multiple                   |  warning at compile-time
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 With GHC 8.x, compiling

 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}

 module A where

 import Language.Haskell.TH

 sep :: Q [Dec]
 sep = [d| x = () |]
 }}}

 and

 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}

 module B where

 import A

 f :: Int
 f = foo

 $(sep)

 foo :: Int
 foo = 3
 }}}

 produces

 {{{
 $ ghc-HEAD/inplace/bin/ghc-stage2 --version
 The Glorious Glasgow Haskell Compilation System, version 8.1.20160303
 $ ghc-HEAD/inplace/bin/ghc-stage2 B.hs
 [1 of 2] Compiling A                ( A.hs, A.o )
 [2 of 2] Compiling B                ( B.hs, B.o )

 B.hs:8:5: error:
     • Variable not in scope: foo :: Int
     • Perhaps you meant ‘foo’ (line 13)
 }}}

 The problem is that when the typechecker constructs the suggestion, it
 uses the
 currently available `GlobalRdrEnv` rather than the one in existence when
 the renamer determined that `foo` is unbound.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11680
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