[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
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        Reporter:  sighingnow        |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  GHCi              |              Version:  8.5
      Resolution:                    |             Keywords:  TypedHoles
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):  Phab:D4909
  #15202                             |
       Wiki Page:                    |
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Comment (by Ömer Sinan Ağacan <omeragacan@…>):

 In [changeset:"39de4e3d33dd9879398062620ad00b1e3b8481ce/ghc"
 39de4e3d/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="39de4e3d33dd9879398062620ad00b1e3b8481ce"
 Fix errors caused by invalid candidates leaking from hole fits

 This is a one line fix (and a note) that fixes four tickets, #15007,
  #15321 and #15202, #15314

 The issue was that errors caused by illegal candidates (according to GHC
 stage or being internal names) were leaking to the user, causing
 bewildering error messages. If a candidate causes the type checker to
 error, it is not a valid hole fit, and should be discarded.

 As mentioned in #15321, this can cause a pattern of omissions, which
 might be hard to discover. A better approach would be to gather the
 error messages, and ask users to report them as GHC bugs. This will be
 implemented in a subsequent change.

 Reviewers: bgamari, simonpj

 Reviewed By: simonpj

 Subscribers: simonpj, rwbarton, thomie, carter

 GHC Trac Issues: #15007, #15321, #15202, #15314

 Differential Revision: https://phabricator.haskell.org/D4909
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15007#comment:12>
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