[GHC] #12127: ghc-8.0.1: panic! (the 'impossible' happened) filterImports/combine (double import)

[GHC]

#12127: ghc-8.0.1: panic! (the 'impossible' happened) filterImports/combine (double
import)
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        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.2
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"393928db9fc35ef8bdeb241c051224a6c4bdf749/ghc"
 393928db/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="393928db9fc35ef8bdeb241c051224a6c4bdf749"
 Fix renamer panic

 This patch fixes Trac #12216 and #12127.  The 'combine' function
 in 'imp_occ_env' in RnNames.filterImports checked for an empty
 field-selector list, which was (a) unnecessary and (b) wrong.

 I've elaborated the comments.

 This does NOT fix #11959 which is related but not the same
 (it concerns bundling of pattern synonyms).
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12127#comment:2>
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