[GHC] #15007: Don't keep shadowed variables in ghci, both renamer and type checker

[GHC]

#15007: Don't keep shadowed variables in ghci, both renamer and type checker
-------------------------------------+-------------------------------------
           Reporter:  sighingnow     |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  GHCi           |           Version:  8.5
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect
  Unknown/Multiple                   |  error/warning at compile-time
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #11547 #14052
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 In ticket:14052, we reverted Phab:D2447, then ticket:11547 exists in HEAD
 again. In ticket:14052#comment:25 and ticket:14052#comment:10, we decide
 that shadowed variables shouldn't be keep at all. This ticket is created
 to track the idea.

 The same error of ticket:11547 was also reported in
 ticket:14996#comment:2,

 > {{{#!hs
 > $ inplace/bin/ghc-stage2 --interactive
 > GHCi, version 8.5.20180403: http://www.haskell.org/ghc/  :? for help
 > Prelude> 1
 > 1
 > Prelude> 1
 > 1
 > Prelude> _
 >
 > <interactive>:1:1: error:
 >     GHC internal error: ‘Ghci1.it’ is not in scope during type >
 checking, but it passed the renamer
 >    tcl_env of environment: []
 >}}}
 >
 > (giving "1" twice is needed to reproduce the error)

 NB: input "1" twice to create shadowed context is necessary to reproduce
 this bug.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15007>
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