[GHC] #12549: Panic on ":t datatypeName"

[GHC]

#12549: Panic on ":t datatypeName"
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        Reporter:  johnleo       |                Owner:  johnleo
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:
       Component:  Compiler      |              Version:  8.1
      Resolution:                |             Keywords:
Operating System:  MacOS X       |         Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
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Comment (by johnleo):

 I've posted my change for review:
 https://phabricator.haskell.org/D2757

 As noted there, this does not fix the `tc_infer_args` problem so we'll
 either have to defer this checkin until that's fixed or change the
 `substTy` in `new_meta_tv_x` back to `substTyUnchecked` and file a new bug
 for `tc_infer_args`.  I wanted to make sure my other changes were okay,
 however.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12549#comment:25>
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