[GHC] #7827: GHC internal error: `a' is not in scope during type checking, but it passed the renamer

[GHC]

#7827: GHC internal error: `a' is not in scope during type checking, but it passed
the renamer
--------------------------------------+-------------------------------------
Reporter:  guest                      |          Owner:                  
    Type:  bug                        |         Status:  new             
Priority:  normal                     |      Component:  Compiler        
 Version:  7.6.2                      |       Keywords:                  
      Os:  Unknown/Multiple           |   Architecture:  Unknown/Multiple
 Failure:  GHC rejects valid program  |      Blockedby:                  
Blocking:                             |        Related:                  
--------------------------------------+-------------------------------------
 In the attached code the following lines give an internal GHC error. At
 least this should not happen. I also think this is valid code. Removing
 either type annotation makes this code compile.

 {{{
 bug :: WrappedR Int -> SomeFunction
 bug (Wrap node) = case node of
   (Memo' (emptyT :: t a b) memoize (Var m) :: R' a b Int) -> -- also
 breaks
 }}}


 {{{
 /Users/alessandro/Documents/Uni/thesis/test/bug-tvar-passed-
 renamer.hs:14:104:
     GHC internal error: `a' is not in scope during type checking, but it
 passed the renamer
     tcl_env of environment: [(am4,
                               Identifier[node::R' a b Int, <NotTopLevel>,
 1]),
                              (rgs,
                               Identifier[bug::WrappedR Int ->
 SomeFunction, <NotTopLevel>, 1])]
     In the type `R' a b Int'
     In a pattern type signature: R' a b Int
     In the pattern:
       Memo' (emptyT :: t a b)
             (memoize :: MVar (t a b) -> (a -> b) -> a -> b)
             (Var m :: R' a b Int) :: R' a b Int
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7827>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler