[GHC] #13250: Backpack: matching newtype selectors doesn't work

[GHC]

#13250: Backpack: matching newtype selectors doesn't work
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        Reporter:  ezyang            |                Owner:  ezyang
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:  duplicate         |             Keywords:  backpack
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 Edward Z. Yang <ezyang@…>):

 In [changeset:"9d17028fbcecb53480598c4fcc7bd9e71b2ac7cf/ghc"
 9d17028f/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="9d17028fbcecb53480598c4fcc7bd9e71b2ac7cf"
 Record full FieldLabel in ifConFields.

 Summary:
 The previous implementation tried to be "efficient" by
 storing field names once in IfaceConDecls, and only just
 enough information for us to reconstruct the FieldLabel.
 But this came at a bit of code complexity cost.

 This patch undos the optimization, instead storing a full
 FieldLabel at each data constructor.  Consequently, this fixes
 bugs #12699 and #13250.

 Signed-off-by: Edward Z. Yang <ezyang at cs.stanford.edu>

 Test Plan: validate

 Reviewers: adamgundry, bgamari, austin

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D3174
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13250#comment:2>
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