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

[GHC]

#12549: Panic on ":t datatypeName"
---------------------------------+--------------------------------------
        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:                |
---------------------------------+--------------------------------------

Comment (by simonpj):

 Yes, all the calls to `substTyUnchecked` indicate places where the in-
 scope set is not properly maintained.   I think most, but not all, of the
 calls to `newMetaTyVarX` do have a correct in-scope set.  As my comment
 says, the one that doesn't is the call from `tc_infer_args`, which is a
 bit of code that (as Richard knows) I do not fully understand.

 Richard: we may need your help to get the in-scope set right here.

 John: which call to `newMetaTyVars` do you think is at fault?  They all
 look ok to me.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12549#comment:19>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler