[GHC] #11970: Simplify Parent for patten synonyms

[GHC]

#11970: Simplify Parent for patten synonyms
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        Reporter:  simonpj           |                Owner:  mpickering
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2179
       Wiki Page:                    |
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Comment (by Matthew Pickering <matthewtpickering@…>):

 In [changeset:"e660f4bf546e90fb6719ad268ca3daaecdce4b82/ghc"
 e660f4bf/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="e660f4bf546e90fb6719ad268ca3daaecdce4b82"
 Rework renaming of children in export lists.

 The target of this patch is exports such as:

 ```
 module Foo ( T(A, B, C) ) where
 ```

 Essentially this patch makes sure that we use the correct lookup functions
 in order
 to lookup the names in parent-children export lists. This change
 highlighted the complexity of this small part of GHC which accounts for
 the scale.

 This change was motivated by wanting to
 remove the `PatternSynonym` constructor from `Parent`. As with all these
 things, it quickly spiraled out of control into a much larger refactor.

 Reviewers: simonpj, goldfire, bgamari, austin

 Subscribers: adamgundry, thomie

 Differential Revision: https://phabricator.haskell.org/D2179

 GHC Trac Issues: #11970
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11970#comment:13>
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