[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:  8.2.1
       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 simonpj):

 I'm not certain, but I thought that `tc_infer_args` was the only caller of
 `new_meta_tv_x` which didn't establish the in-scope set.

 There are lots of `substTyUnchecked` which each need individual attention.
 I suppose a new ticket that enumerated them would be a good thing.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12549#comment:30>
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