[GHC] #15994: Duplicate entries in -ddump-minimal-imports

[GHC]

#15994: Duplicate entries in -ddump-minimal-imports
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.3
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"84cba4bce65ffc99e2356b3621cf91258b055cad/ghc" 84cba4b/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="84cba4bce65ffc99e2356b3621cf91258b055cad"
 Remove duplicates in -ddump-minimial-imports

 This fixes Trac #15994.

 Previously RdrName.gresToAvailInfo assumed that the input list
 of GREs had no duplicates. I accidentally broke this precondition
 in this refactoring:

     commit 6353efc7694ba8ec86c091918e02595662169ae2
     Date:   Thu Nov 22 14:48:05 2018 -0500

     Fix unused-import warnings

     This patch fixes a fairly long-standing bug (dating back to 2015) in
     RdrName.bestImport, namely

 (There was an ASSERT, but it's usually switched off in stage2.  It
 tripped when I switched stage2 assertions on.)

 The fix is straightforward: account for dups in gresToAvailInfo.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15994#comment:1>
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